Acute respiratory failure: type 1 vs type 2, oxygen therapy, and when to intubate

Cinematic clinical scene with an arterial blood gas syringe and result slip, a labelled diagram contrasting hypoxaemic type 1 and hypercapnic type 2 respiratory failure, an oxygen mask and a BiPAP machine, clinical-blue lighting, no faces, no text — FigureRespiratory failure — type 1 (hypoxaemic, PaO2 under 60, normal PaCO2, an elevated A-a gradient) versus type 2 (hypercapnic, PaCO2 over 45, a normal A-a gradient and alveolar hypoventilation). The A-a gradient and the response to oxygen separate the lung problem from the pump problem.

Type 1 vs Type 2 respiratory failure

Feature	Type 1 (Hypoxaemic)	Type 2 (Hypercapnic)
Definition	PaO2 <60 mmHg (8 kPa) with NORMAL/LOW PaCO2	PaCO2 >45 mmHg (6 kPa) ± hypoxaemia
Mechanism	V/Q mismatch, shunt, diffusion impairment, low FiO2	ALVEOLAR HYPOVENTILATION (not enough air moved to clear CO2)
A-a gradient	ELEVATED (>20 mmHg — lung problem — gas exchange impaired)	NORMAL (<15 — normal lungs — just not breathing enough — CO2 accumulates)
Common causes	Pneumonia, ARDS, PE, pulmonary oedema, asthma, pulmonary fibrosis	COPD, opioid overdose, neuromuscular (GBS, MG, motor neuron), obesity hypoventilation, chest wall (kyphoscoliosis), sleep apnoea
Oxygen target	SpO2 92-96% (PaO2 60-80) — high-flow if needed	SpO2 88-92% (CO2 retainer — too much O2 → loss of hypoxic drive → CO2 rises)
NIV	CPAP (for cardiogenic pulmonary oedema — 3CPO; for ARDS if moderate)	BiPAP (IPAP/EPAP — ventilatory support — for COPD with acidosis — PLANT trial)
When to intubate	PaO2/FiO2 <150 despite O2/HFNC/NIV; refractory hypoxaemia	NIV failing (worsening PaCO2, pH <7.25, exhaustion); GCS <8 (can't protect airway)

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Assessment and management of acute respiratory failure

RECOGNISE + ASSESS (ABG) — (a) CLINICAL: dyspnoea, tachypnoea (RR >25 — or bradypnoea [<8] — ominous — fatigue/impending arrest), accessory muscle use, cyanosis (late), altered consciousness (hypoxia/hypercapnia → confusion → coma), exhaustion (paradoxical breathing — abdominal wall moves INWARD on inspiration — diaphragm not working). (b) ABG (the key diagnostic test): (i) PaO2 (LOW in both types — <60 = type 1; low + with high CO2 = type 2). (ii) PaCO2 (NORMAL/LOW in type 1 [hyperventilating to compensate for hypoxaemia — blowing off CO2]; HIGH in type 2 [hypoventilating → CO2 accumulates]). (iii) pH (LOW in type 2 if severe [<7.35 — respiratory acidosis from CO2 retention — pH <7.25 = severe — needs NIV/intubation]). (iv) A-a GRADIENT: calculated = PAO2 − PaO2 (where PAO2 = FiO2 × [713 − 47] − PaCO2/0.8). ELEVATED (>20) = gas exchange problem (V/Q mismatch/shunt — lung disease). NORMAL (<15) = hypoventilation (normal lungs — brain/muscle/chest wall problem — just not moving enough air). (c) CXR (identify cause — pneumonia/ARDS/effusion/pneumothorax/pulmonary oedema). (d) CLASSIFY: TYPE 1 (PaO2 <60, PaCO2 normal/low, A-a elevated) vs TYPE 2 (PaCO2 >45 ± hypoxaemia, A-a may be normal [pure hypoventilation] or elevated [COPD has BOTH hypoventilation AND V/Q mismatch]). (e) HISTORY: COPD (exacerbation), pneumonia (fever, cough, purulent sputum), ARDS (sepsis, trauma, aspiration), PE (pleuritic pain, DVT), heart failure (orthopnoea, PND, oedema), opioid (addict, palliative), neuromuscular (progressive weakness), sleep apnoea (obesity, snoring)
TYPE 1 — OXYGEN + TREAT CAUSE + ESCALATE — (a) OXYGEN: target SpO2 92-96% (PaO2 60-80). Start with NASAL SPECS (2-6 L/min → FiO2 24-44%) → SIMPLE MASK (5-10 L/min → 35-60%) → NON-REBREATHER (10-15 L/min → 60-90%) → HIGH-FLOW NASAL CANNULA (HFNC — up to 60 L/min → FiO2 up to 100% — FLORALI: HFNC vs standard O2/NIV → HFNC trend to lower intubation [especially PaO2/FiO2 <200]). (b) TREAT CAUSE: (i) PNEUMONIA → antibiotics (CAP — ceftriaxone + azithromycin). (ii) ARDS → lung-protective ventilation (if intubated — Vt 6 mL/kg). (iii) PE → anticoagulation/thrombolysis. (iv) PULMONARY OEDEMA (cardiogenic) → frusemide + vasodilator + CPAP (3CPO). (v) ASTHMA → bronchodilators + steroids. (c) NIV/CPAP: (i) CPAP (5-10 cmH2O) for CARDIOGENIC PULMONARY OEDEMA (3CPO trial — CPAP reduces intubation — mechanism: positive pressure → reduced preload + afterload → improved cardiac output + reduced pulmonary oedema). (ii) CPAP for MODERATE ARDS (PaO2/FiO2 200-300 — may improve oxygenation — but NOT for severe [<150 — needs intubation]). (iii) HFNC (FLORALI — preferred over NIV for hypoxaemic respiratory failure — more comfortable — trend to lower intubation). (d) INTUBATE IF: (i) PaO2/FiO2 <150 despite HFNC/NIV (refractory hypoxaemia — lung can't oxygenate even with support — needs mechanical ventilation with PEEP). (ii) Worsening (SpO2 <90% despite FiO2 ≥60%). (iii) Exhaustion (RR >35, accessory muscles, paradoxical breathing, falling tidal volume). (iv) Altered consciousness (can't protect airway — aspiration risk). (v) Haemodynamic instability (shock — positive pressure ventilation reduces work of breathing + allows sedation/vasopressors). (e) KEY: type 1 → oxygen (titrate to SpO2 92-96%) + HFNC/CPAP + treat cause + intubate if refractory
TYPE 2 — BiPAP + CONTROLLED OXYGEN + TREAT CAUSE — (a) OXYGEN: target SpO2 88-92% (NOT 94-98% — controlled oxygen for CO2 retainers). WHY: (i) In COPD, chronic CO2 retention → central respiratory drive becomes less sensitive to CO2 → hypoxic drive (low PaO2 → stimulates breathing) becomes IMPORTANT. (ii) If you give TOO MUCH oxygen → PaO2 rises → removes hypoxic drive → patient breathes LESS → PaCO2 RISES (worsens hypercapnia → CO2 narcosis → coma → respiratory arrest). (iii) CONTROLLED OXYGEN (Venturi mask — precise FiO2 — 24% or 28% — to maintain PaO2 just adequate [SpO2 88-92%] without suppressing hypoxic drive). (iv) The 'hypoxic drive' theory is somewhat OVERSTATED (the main mechanism of O2-induced hypercapnia is V/Q mismatch — high FiO2 → vasodilates poorly ventilated alveoli [where CO2 is high] → blood flows to these units → 'picks up' CO2 → worsens hypercapnia — NOT just loss of hypoxic drive — but controlled oxygen is STILL recommended). (b) NIV (BiPAP): (i) BiPAP (Bilevel Positive Airway Pressure): IPAP (inspiratory — 10-15 cmH2O) + EPAP (expiratory [PEEP] — 4-6 cmH2O). (ii) MECHANISM: IPAP provides INSPIRATORY PRESSURE SUPPORT → augments each breath → more tidal volume → more ventilation → clears CO2. EPAP (PEEP) splints airways open → reduces work of breathing → prevents alveolar collapse. (iii) INDICATION: PaCO2 >45 + pH <7.35 (respiratory acidosis) — COPD exacerbation with hypercapnic acidosis — the BEST evidence for NIV. (iv) PLANT TRIAL (2000, Lancet): NIV (BiPAP) vs standard therapy (oxygen) for COPD with pH 7.25-7.35 → NIV reduced: need for intubation, in-hospital mortality, complications. NIV is STANDARD for COPD with hypercapnic acidosis. (v) OTHER TYPE 2: neuromuscular (GBS — NIV if progressive weakness — but often needs intubation if bulbar/respiratory muscle weakness severe); obesity hypoventilation (BiPAP — chronic); opioid overdose (naloxone — reverse — don't need NIV if reverses). (c) TREAT CAUSE: (i) COPD → bronchodilators (salbutamol + ipratropium nebulised) + steroids (prednisolone 30 mg PO/IV) + antibiotics (if bacterial infection — amoxicillin/doxycycline). (ii) OPIOID → NALOXONE (0.4-0.8 mg IV/IM — reverse opioid → restores respiratory drive → may need infusion if long-acting opioid [methadone] or sustained-release). (iii) NEUROMUSCULAR (GBS) → IVIG/plasma exchange + monitor respiratory function (FVC, NIF — if declining → intubate BEFORE crisis — prophylactic intubation better than emergency). (d) INTUBATE IF: (i) NIV FAILING (worsening PaCO2 despite BiPAP — or pH <7.25 despite BiPAP — or patient can't tolerate BiPAP). (ii) GCS <8 (can't protect airway — aspiration risk — CO2 narcosis). (iii) Exhaustion (progressive bradypnoea — RR <8 — or accessory muscle fatigue). (iv) HAEMODYNAMIC instability (shock — positive pressure ventilation reduces work). (v) Bulbar weakness (neuromuscular — can't swallow/clear secretions — aspiration). (e) KEY: type 2 → controlled oxygen (88-92%) + BiPAP (if hypercapnic acidosis) + treat cause (bronchodilators/steroids for COPD; naloxone for opioid) + intubate if NIV fails/exhaustion/coma
OXYGEN DELIVERY DEVICES — KNOW THE CASCADE — (a) NASAL SPECS (cannula): 1-6 L/min → FiO2 24-44% (each L/min adds ~4% FiO2). Low-flow. Comfortable. Patient eats/talks. Best for: mild hypoxaemia (SpO2 90-92%). (b) SIMPLE MASK: 5-10 L/min → FiO2 35-60%. Needs ≥5 L/min (to wash out CO2 from mask — prevent rebreathing). Best for: moderate hypoxaemia. (c) NON-REBREATHER MASK (with reservoir bag): 10-15 L/min → FiO2 60-90% (one-way valves prevent exhaled air from re-entering bag → highest FiO2 from a mask). Best for: SEVERE hypoxaemia (emergency — while preparing HFNC/NIV/intubation). (d) VENTURI MASK: precise FiO2 (24%, 28%, 35%, 40%, 50% — colour-coded — fixed-performance — entrainment valves deliver EXACT FiO2 regardless of patient's breathing pattern). Best for: COPD/CO2 retainers (precise controlled FiO2 — 24% or 28% — to maintain SpO2 88-92% without worsening hypercapnia). (e) HIGH-FLOW NASAL CANNULA (HFNC): up to 60 L/min flow + FiO2 21-100% (heated humidified). MECHANISM: washes out dead space (reduces CO2 rebreathing) + PEEP effect (3-5 cmH2O from high flow) + reduces work of breathing + comfortable. FLORALI: HFNC vs standard O2 → trend to lower intubation (especially PaO2/FiO2 <200). Best for: MODERATE type 1 respiratory failure (PaO2/FiO2 200-300) — bridge — before intubation. (f) NIV (BiPAP/CPAP): provides VENTILATORY SUPPORT (BiPAP — for type 2) or POSITIVE PRESSURE (CPAP — for type 1/pulmonary oedema). (g) MECHANICAL VENTILATION (invasive — intubated): the most support — full control of ventilation + oxygenation — but invasive (VAP, sedation, ICU-acquired weakness). (h) KEY: escalate: nasal specs → mask → non-rebreather → HFNC → NIV → intubation. Choose based on: severity (SpO2/PaO2/PaCO2), type (1 vs 2), cause, patient tolerance
WHEN TO INTUBATE — THE DECISION — (a) GENERAL CRITERIA (any of): (i) AIRWAY COMPROMISE: GCS <8 (can't protect airway — aspiration risk — from hypoxia/hypercapnia/encephalopathy). (ii) REFRACTORY HYPOXAEMIA: PaO2/FiO2 <150 despite HFNC/NIV (lung can't oxygenate even with support). OR SpO2 <90% despite FiO2 ≥60%. (iii) RESPIRATORY ACIDOSIS: pH <7.25 (from CO2 retention — despite NIV/BiPAP — if BiPAP failing). (iv) EXHAUSTION: progressive fatigue — paradoxical breathing (abdomen moves INWARD on inspiration — diaphragm not functioning — pre-terminal — about to arrest), RR falling (bradypnoea — <8 — from fatigue — ominous), decreasing tidal volume (shallow breathing — can't maintain ventilation). (v) HAEMODYNAMIC INSTABILITY: shock (hypotension — from hypoxia-induced cardiac dysfunction OR the cause itself — positive pressure ventilation reduces work of breathing → reduces O2 demand → helps heart + allows sedation/vasopressors). (vi) FAILURE OF NON-INVASIVE: NIV/HFNC failing (worsening ABG, worsening clinical — don't delay intubation — DELAYED intubation is worse than early). (b) TYPE 1 SPECIFIC: PaO2/FiO2 <150 despite HFNC/NIV/CPAP → intubate + lung-protective ventilation (PEEP to maintain alveolar recruitment). (c) TYPE 2 SPECIFIC: NIV failing (PaCO2 rising despite BiPAP) OR pH <7.25 despite BiPAP OR GCS <8 (CO2 narcosis) → intubate + mechanical ventilation (low Vt + controlled rate). (d) NEUROMUSCULAR (GBS/MG): PROPHYLACTIC intubation if declining respiratory function (FVC <15-20 mL/kg OR NIF below −25 cmH2O OR bulbar weakness [can't swallow/clear secretions]). DON'T wait for crisis — intubate BEFORE respiratory arrest (prophylactic intubation better than emergency). (e) KEY: don't DELAY intubation (if NIV/HFNC failing → intubate SOONER rather than waiting — DELAYED intubation → worse outcomes — the patient deteriorates further → more difficult intubation [physiologically — worse hypoxia/acidosis → harder to intubate → cardiac arrest on induction]). (f) PRACTICE: trial NIV/HFNC (if appropriate) → reassess at 1-2h → if improving → continue → if worsening → INTUBATE (don't keep trying NIV if failing — each hour of failure → worse outcomes)
TREAT CAUSE + SUPPORTIVE — (a) TREAT CAUSE (the most important — respiratory failure is a SYMPTOM of an underlying condition — unless cause treated → respiratory failure persists → won't wean from ventilator): (i) PNEUMONIA → antibiotics (within 1h if septic). (ii) COPD → bronchodilators + steroids. (iii) ASTHMA → bronchodilators + steroids + magnesium. (iv) ARDS → treat trigger (sepsis, trauma, aspiration) + lung-protective ventilation. (v) PE → anticoagulation ± thrombolysis. (vi) PULMONARY OEDEMA → diuretics + treat cardiac cause (ACS, valve, arrhythmia). (vii) OPIOID → naloxone. (viii) NEUROMUSCULAR → IVIG/plasma exchange (GBS, MG). (ix) SEPSIS → antibiotics + source control + fluids + vasopressors (sepsis causes respiratory failure via ARDS + muscular fatigue + encephalopathy). (b) SUPPORTIVE (while cause treated + ventilated): (i) SEDATION (if intubated — propofol/midazolam — minimize — daily SAT). (ii) POSITION (head up 30° — prevents VAP + improves diaphragmatic excursion). (iii) NUTRITION (early enteral — within 48h — maintains respiratory muscle strength + gut barrier). (iv) DVT PROPHYLAXIS (LMWH — immobilised + ventilated = high VTE risk). (v) STRESS ULCER PROPHYLAXIS (PPI — if ventilated >48h or coagulopathy). (vi) GLYCAEMIC CONTROL (6-10 — NICE-SUGAR). (vii) FLUID MANAGEMENT (conservative — FACTT — less fluid → less pulmonary oedema → better oxygenation + ventilation — but maintain perfusion). (viii) PHYSIOTHERAPY (secretion clearance — especially COPD/pneumonia). (c) WEANING (once cause resolving): SAT + SBT daily (ABC trial — reduces ventilation days + mortality). (d) KEY: treat CAUSE (the most important — respiratory failure resolves as cause resolves) + supportive care (sedation, nutrition, VAP prevention) + wean when ready

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SAQ — COPD exacerbation with oxygen-induced hypercapnia

10 minutes · 10 marks

A 72-year-old man with severe COPD (FEV1 35 per cent predicted, on home oxygen 2 L/min and tiotropium) is brought to the emergency department after 3 days of increasing dyspnoea, purulent sputum and wheeze following a viral upper respiratory infection. A concerned paramedic gave him high-flow oxygen (15 L/min via non-rebreather) for an initial SpO2 of 84 per cent. On arrival in the emergency department he is drowsy (GCS 13), cyanotic, and has slow shallow breathing (RR 8) with a prolonged expiratory phase and bilateral wheeze. ABG on 15 L/min NRBM: pH 7.18, PaCO2 92 mmHg, PaO2 78 mmHg, bicarbonate 34 mmol/L, base excess plus 8. The A-a gradient is calculated to be 18 mmHg. BP 152/86, HR 96 in sinus rhythm. CXR shows hyperinflated lungs with no focal consolidation.

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SAQ — Guillain-Barre syndrome with declining FVC (neuromuscular respiratory failure)

10 minutes · 10 marks

A 38-year-old woman is admitted to hospital with a 6-day history of progressive ascending weakness following a diarrhoeal illness 2 weeks earlier (Campylobacter jejuni). She has bilateral facial nerve palsies, areflexic quadriparesis (MRC grade 3 in the upper limbs, grade 2 in the lower limbs), and complains of difficulty clearing secretions and shortness of breath when lying flat. She is alert and oriented. Vital signs: RR 18, SpO2 96 per cent on room air, HR 92, BP 142/86. Bedside spirometry: FVC 18 mL/kg (1.1 L), NIF minus 28 cmH2O (peak negative inspiratory force), peak expiratory flow 180 L/min. ABG on room air: pH 7.38, PaCO2 48 mmHg, PaO2 76 mmHg, bicarbonate 28 mmol/L. The A-a gradient is 12 mmHg.

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Clinical pearls

High-yield respiratory failure points for CICM/FFICM exam

Type 1 vs Type 2 — the fundamental distinction. (1) TYPE 1 (HYPOXAEMIC): (a) PaO2 <60 mmHg (8 kPa) with NORMAL or LOW PaCO2. (b) MECHANISM: GAS EXCHANGE PROBLEM — lung can't transfer oxygen to blood (from V/Q mismatch, shunt, diffusion impairment). (c) CAUSES: pneumonia (V/Q mismatch — pus in alveoli → blood flows past unventilated alveoli → low O2 in blood), ARDS (shunt — fluid-filled alveoli → blood can't pick up O2 even with 100% FiO2), PE (V/Q mismatch — ventilated but not perfused → dead space → less O2 uptake), pulmonary oedema (diffusion impairment → fluid in alveoli → impaired O2 diffusion), asthma (V/Q mismatch — bronchospasm → heterogeneous ventilation → mismatch), pulmonary fibrosis (diffusion impairment → thickened alveolar-capillary membrane → O2 can't diffuse), high altitude (low inspired FiO2 — not enough O2 in air). (d) COMPENSATION: patient HYPERVENTILATES (blows off CO2 → PaCO2 normal/low) → maintains SOME oxygenation (the extra ventilation partially compensates for the gas exchange deficit). (e) A-a gradient: ELEVATED (>20) — the alveoli have O2 (ventilation is adequate) but blood can't pick it up (transfer impaired) → gradient between alveolar O2 (high) and arterial O2 (low). (2) TYPE 2 (HYPERCAPNIC): (a) PaCO2 >45 mmHg (6 kPa) ± hypoxaemia. (b) MECHANISM: ALVEOLAR HYPOVENTILATION — not enough air moved in and out of lungs → CO2 accumulates (not cleared) + O2 drops (not replenished). (c) CAUSES: COPD (airflow obstruction → can't move enough air → CO2 retention — MOST COMMON), opioid overdose (respiratory centre depression → reduced drive → hypoventilation), neuromuscular (GBS, MG, motor neuron disease, muscular dystrophy — respiratory muscle weakness → can't generate adequate tidal volume), obesity hypoventilation syndrome (excess weight on chest wall → increased work → inadequate ventilation), kyphoscoliosis (restrictive chest wall → reduced lung capacity), sleep apnoea (upper airway obstruction during sleep → intermittent hypoventilation), brainstem injury (respiratory centre damage → reduced drive). (d) COMPENSATION: can't compensate (the problem IS the ventilation — if you're hypoventilating, you can't 'hyperventilate more' to compensate — the mechanism is broken). (e) A-a gradient: NORMAL (<15) in PURE hypoventilation (the lungs are normal — gas exchange works fine — but not enough air is being moved → CO2 accumulates → O2 drops — both proportional — A-a gradient normal). BUT: COPD often has BOTH (hypoventilation from obstruction + V/Q mismatch from heterogeneous ventilation → A-a gradient may be elevated too — COPD is a MIXED picture). (3) KEY: type 1 = gas exchange problem (hypoxaemia + normal/low CO2 + high A-a) — lung disease. Type 2 = hypoventilation (high CO2 ± hypoxaemia + normal A-a) — brain/muscle/chest wall problem (or COPD — mixed).[1]
A-a gradient — the diagnostic tool. (1) FORMULA: A-a gradient = PAO2 (alveolar O2) − PaO2 (arterial O2). PAO2 = FiO2 × (Patm − PH2O) − PaCO2/R. Where: FiO2 = fraction of inspired O2 (room air = 0.21). Patm = atmospheric pressure (760 mmHg at sea level). PH2O = water vapour pressure (47 mmHg). PaCO2 = arterial CO2. R = respiratory quotient (0.8). SIMPLIFIED (room air): PAO2 = 0.21 × (760 − 47) − PaCO2/0.8 = 150 − PaCO2/0.8. (2) EXAMPLE (normal): PaCO2 = 40, PaO2 = 95. PAO2 = 150 − 40/0.8 = 150 − 50 = 100. A-a = 100 − 95 = 5 (NORMAL — <15). (3) EXAMPLE (type 1): PaCO2 = 30 (hyperventilating — compensation), PaO2 = 50 (hypoxaemic). PAO2 = 150 − 30/0.8 = 150 − 37.5 = 112.5. A-a = 112.5 − 50 = 62.5 (ELEVATED — lung problem — O2 in alveoli [112.5] but not reaching blood [50]). (4) EXAMPLE (type 2 — pure hypoventilation): PaCO2 = 80 (severe hypercapnia — opioid overdose), PaO2 = 50. PAO2 = 150 − 80/0.8 = 150 − 100 = 50. A-a = 50 − 50 = 0 (NORMAL — the alveoli have the SAME O2 as the blood — the problem is NOT gas exchange — it's hypoventilation — both PAO2 and PaO2 are low because not enough air is being moved — the lungs work fine — the brain/muscle is the problem). (5) USE: A-a gradient DISTINGUISHES lung problems (elevated — V/Q mismatch, shunt, diffusion) from non-lung problems (normal — hypoventilation from brain/muscle/chest wall). ALSO: helps with DIFFERENTIAL — elevated A-a → think lung disease (pneumonia, ARDS, PE, oedema, fibrosis); normal A-a → think hypoventilation (opioid, neuromuscular, obesity, brainstem). (6) AGE ADJUSTMENT: normal A-a increases with age (formula: A-a = age/4 + 4). A 60-year-old has normal A-a up to ~19 (60/4 + 4 = 19). Don't over-interpret mild elevation in elderly. (7) KEY: A-a gradient — elevated (>20) = lung problem (gas exchange impaired — O2 in alveoli but not reaching blood); normal (<15) = hypoventilation (normal lungs — just not breathing enough).[1]
Oxygen targets — type 1 vs type 2. (1) TYPE 1: SpO2 92-96% (PaO2 60-80 mmHg). (a) GIVE ENOUGH OXYGEN — the problem is OXYGENATION (lung can't transfer O2) → need high FiO2 to maximise O2 delivery. (b) DON'T chase SpO2 100% — hyperoxia (too much O2) → oxidative stress (free radicals) + absorption atelectasis (nitrogen washout → alveoli collapse) + CO2 retention (V/Q mismatch — high FiO2 → vasodilates poorly ventilated alveoli → blood flows to these → picks up CO2). (c) BTS GUIDELINE (2017): target SpO2 94-98% for most acutely ill (or 92-96% if at risk of hypercapnia). NICE-SUGAR (ICU): 92-96%. ICUROX: conservative (SpO2 ≤97) → trend to lower mortality. (2) TYPE 2 (CO2 RETAINER — COPD): SpO2 88-92% (NOT higher). (a) WHY CONTROLLED: (i) HYPOXIC DRIVE: in chronic CO2 retainers → central respiratory drive becomes less responsive to CO2 → HYPOXIC DRIVE (low PaO2 → stimulates breathing) becomes important → giving high FiO2 → removes hypoxic drive → patient breathes LESS → PaCO2 RISES → CO2 narcosis → coma → respiratory arrest. (ii) V/Q MISMATCH (the MAIN mechanism — more important than hypoxic drive): high FiO2 → vasodilates pulmonary vessels supplying POORLY VENTILATED alveoli (where CO2 is high) → more blood flows to these high-CO2 units → 'picks up' CO2 → worsens hypercapnia. (iii) HALDANE EFFECT: high FiO2 → O2 displaces CO2 from haemoglobin → more CO2 in plasma (free) → worsens hypercapnia. (b) HOW: VENTURI MASK (24% or 28% — precise FiO2 — for COPD) — NOT nasal specs (imprecise — patient's breathing pattern varies FiO2). (c) MONITOR: ABG at 30-60 min after starting oxygen → check PaCO2 (if rising → reduce FiO2 → start BiPAP). (d) DON'T WITHHOLD OXYGEN from a hypoxaemic COPD patient (hypoxaemia KILLS faster than hypercapnia — give enough to maintain SpO2 88-92% — but CONTROLLED — Venturi — monitor ABG). (3) KEY: type 1 → SpO2 92-96% (enough O2 — but don't chase 100%). Type 2 (CO2 retainer) → SpO2 88-92% (controlled — Venturi — to prevent O2-induced hypercapnia — BUT give enough — hypoxaemia kills faster than hypercapnia).[5]
NIV (BiPAP) for type 2 — PLANT trial. (1) BiPAP (Bilevel Positive Airway Pressure): IPAP (inspiratory — pressure support — 10-15 cmH2O) + EPAP (expiratory [PEEP] — 4-6 cmH2O). (2) MECHANISM: (a) IPAP provides PRESSURE SUPPORT during each inspiration → augments the patient's own effort → larger tidal volume → more ventilation → clears CO2 → improves hypercapnia. (b) EPAP (PEEP) splints airways open → reduces work of breathing → prevents alveolar collapse → improves oxygenation. (c) Reduces work of breathing → rests fatigued muscles → allows recovery. (3) INDICATION: type 2 respiratory failure with ACIDOSIS (PaCO2 >45 + pH <7.35). (a) BEST EVIDENCE: COPD exacerbation with pH 7.25-7.35 → BiPAP. (b) PLANT TRIAL (2000, Lancet): BiPAP vs standard therapy (controlled oxygen) for COPD with pH 7.25-7.35 → BiPAP REDUCED: need for intubation (15% vs 27%), in-hospital mortality (10% vs 20%), complications. BiPAP is STANDARD for COPD with hypercapnic acidosis. (c) OTHER TYPE 2: (i) NEUROMUSCULAR (GBS, MG) → BiPAP if progressive weakness but NO bulbar involvement (can protect airway). But often needs intubation if bulbar (can't swallow) or rapidly progressing. (ii) OPIOID OVERDOSE → naloxone (not BiPAP — reverse the cause — unless mixed/long-acting). (iii) OBESITY HYPOVENTILATION → BiPAP (chronic + acute). (4) CONTRAINDICATIONS (for NIV): (a) GCS <8 (can't protect airway → aspiration). (b) Facial trauma/deformity (mask leak — can't seal). (c) Haemodynamic instability (shock — NIV may worsen). (d) Active vomiting/aspiration risk. (e) Inability to clear secretions (can't cough — secretions pool behind mask). (f) Agitation/uncooperative (can't tolerate mask). (g) Pneumothorax (relative — CPAP/EPAP may worsen — but chest tube first → then NIV). (5) WHEN TO STOP NIV (switch to intubation): (a) Worsening ABG (PaCO2 rising, pH falling — despite adequate BiPAP settings). (b) Deteriorating clinical (worsening exhaustion, agitation, decreasing consciousness). (c) NIV intolerance (can't keep mask on — claustrophobic — leaks — skin breakdown). (d) Don't prolong NIV trial beyond 1-2h if clearly failing (DELAYED intubation is worse than early). (6) KEY: BiPAP for type 2 with acidosis (PLANT — reduces intubation + mortality for COPD). NOT for GCS <8 or aspiration risk (intubate). Intubate if failing at 1-2h.[3]
HFNC — FLORALI trial. (1) HFNC (High-Flow Nasal Cannula): delivers heated, humidified oxygen at HIGH FLOW (up to 60 L/min) via nasal cannula. FiO2 adjustable (21-100%). (2) MECHANISM: (a) WASHOUT of dead space (high flow flushes CO2 from upper airway/anatomical dead space → reduces rebreathing → lowers PaCO2 + reduces work of breathing). (b) PEEP EFFECT (3-5 cmH2O from high flow through nasal passages → maintains alveolar recruitment → improves oxygenation). (c) REDUCED WORK OF BREATHING (heated humidified gas — easier to inspire — less respiratory effort). (d) MATCHES inspiratory demand (high flow meets patient's peak inspiratory flow → no air hunger → less tachypnoea → more efficient breathing). (e) REDUCES inspiratory resistance (cannula provides flow — reduces negative pressure the patient must generate). (3) FLORALI (2015, NEJM): HFNC vs standard O2 (face mask) vs NIV in immunocompromised + ARDS patients (PaO2/FiO2 <300). RESULT: (a) HFNC trend to LOWER intubation rate (38% vs 47% vs 50% — not significant overall but significant in PaO2/FiO2 <200 subgroup). (b) HFNC LOWER mortality (especially PaO2/FiO2 <200 — significant subgroup). (c) HFNC more COMFORTABLE (patient preference — less claustrophobic than NIV mask). (4) ROX INDEX (SpO2/FiO2 / RR): (a) After 2h of HFNC. (b) ROX <3.85 → HIGH risk of intubation (consider intubating). (c) ROX >4.88 → LIKELY to succeed (continue HFNC). (d) Use ROX to DECIDE — trial HFNC → reassess at 2h → if ROX low → intubate (don't delay). (5) WHEN TO INTUBATE (HFNC failure): worsening hypoxaemia (SpO2 <90% despite FiO2 100%), rising RR (>35), exhaustion, altered consciousness, ROX <3.85. (6) KEY: HFNC for moderate type 1 respiratory failure (PaO2/FiO2 200-300) — FLORALI — trend to lower intubation + mortality. Use ROX index at 2h to decide. Don't delay intubation if failing.[2]
When to intubate — the key decision. (1) AIRWAY: GCS <8 → intubate (can't protect airway — aspiration risk). (2) OXYGENATION: PaO2/FiO2 <150 despite HFNC/NIV/CPAP → intubate (refractory hypoxaemia — lung can't oxygenate → needs PEEP from mechanical ventilation). OR SpO2 <90% despite FiO2 ≥60%. (3) VENTILATION: PaCO2 rising despite BiPAP/NIV → intubate (can't clear CO2 non-invasively). OR pH <7.25 despite NIV. (4) EXHAUSTION: RR >35 + accessory muscle use + falling tidal volume → about to arrest → intubate NOW (don't wait for bradypnoea/cardiac arrest — intubate BEFORE arrest). (5) HAEMODYNAMICS: shock + respiratory failure → intubate (positive pressure reduces work of breathing → reduces O2 demand → helps heart + allows sedation/vasopressors without respiratory depression concern). (6) NEUROMUSCULAR: FVC <15-20 mL/kg OR NIF below −25 cmH2O OR bulbar weakness → PROPHYLACTIC intubation (before crisis — prophylactic intubation better than emergency). (7) PRACTICE: (a) Trial HFNC/NIV (if appropriate — type 1 → HFNC; type 2 → BiPAP). (b) Reassess at 1-2h. (c) If IMPROVING → continue. (d) If WORSENING → INTUBATE (don't delay — delayed intubation → worse outcomes — each hour of failure → more physiological deterioration → harder to intubate [worse hypoxia/acidosis → cardiac arrest on induction]). (8) KEY: intubate for: GCS <8 (airway), PaO2/FiO2 <150 (oxygenation), pH <7.25 despite NIV (ventilation), exhaustion (pre-arrest), shock (haemodynamic), neuromuscular decline (prophylactic). DON'T DELAY — trial NIV/HFNC → reassess at 1-2h → if failing → intubate NOW.[6]
Oxygen-induced hypercapnia — the COPD trap. (1) THE PHENOMENON: giving high-concentration oxygen to a COPD patient → PaCO2 RISES → respiratory acidosis → CO2 narcosis → coma → respiratory arrest. (2) MECHANISMS (3 — all contribute): (a) LOSS OF HYPOXIC DRIVE (classic explanation — but OVERSTATED): (i) In chronic CO2 retention → central respiratory centre becomes less responsive to CO2 (chronic high CO2 → downregulates CO2 chemoreceptors → CO2 no longer drives breathing). (ii) HYPOXIC DRIVE (low PaO2 → stimulates peripheral chemoreceptors [carotid body] → maintains breathing) becomes the PRIMARY drive. (iii) Giving high FiO2 → PaO2 rises → removes hypoxic drive → patient breathes LESS → PaCO2 RISES. (iv) This mechanism accounts for ~25% of O2-induced hypercapnia (important but NOT the main mechanism). (b) V/Q MISMATCH (the MAIN mechanism — ~50%): (i) In COPD: lungs have HETEROGENEOUS ventilation — some alveoli well-ventilated (high V/Q), others poorly ventilated (low V/Q — from obstruction/emphysema). (ii) NORMAL: hypoxic pulmonary vasoconstriction (HPV) → blood diverted AWAY from poorly ventilated alveoli (low O2 → vasoconstrict → blood goes to well-ventilated alveoli → gas exchange optimised). (iii) Giving high FiO2 → raises alveolar O2 in POORLY ventilated alveoli → RELIEVES hypoxic vasoconstriction → blood FLOWS BACK to these poorly ventilated alveoli → blood 'picks up' CO2 (from these units that have high CO2) → PaCO2 RISES. (iv) Net: high FiO2 → worsens V/Q mismatch → more CO2 in blood. (c) HALDANE EFFECT (~25%): (i) CO2 is transported in blood 3 ways: dissolved (10%), as bicarbonate (60%), bound to haemoglobin (30% — as carbamino compounds). (ii) When O2 binds to haemoglobin → it DISPLACES CO2 from haemoglobin (the Haldane effect — O2 and CO2 compete for binding sites). (iii) Giving high FiO2 → more O2 binds haemoglobin → more CO2 displaced from haemoglobin → more FREE CO2 in plasma → PaCO2 rises. (iv) This is the least significant of the 3 mechanisms but contributes. (3) MANAGEMENT: (a) CONTROLLED OXYGEN: Venturi mask (24% or 28% — precise FiO2) → maintain SpO2 88-92% (give enough to prevent hypoxaemia — hypoxaemia kills faster than hypercapnia — but don't over-oxygenate). (b) MONITOR ABG at 30-60 min → if PaCO2 rising → reduce FiO2 + start BiPAP. (c) BiPAP: provides ventilatory support → helps clear CO2 even if oxygen-induced hypercapnia occurs. (4) KEY: oxygen-induced hypercapnia in COPD is from: V/Q MISMATCH (main — 50%), loss of hypoxic drive (25%), Haldane effect (25%). Management: controlled oxygen (Venturi — 24-28% — SpO2 88-92%) + BiPAP + monitor ABG.[5]
Shunt vs V/Q mismatch — oxygen response. (1) V/Q MISMATCH (most common cause of hypoxaemia): (a) V/Q = ratio of ventilation (V) to perfusion (Q). (b) LOW V/Q (ventilation < perfusion): blood flows past alveoli that aren't adequately ventilated (pneumonia, COPD, asthma, atelectasis) → blood doesn't pick up enough O2 → hypoxaemia. (c) HIGH V/Q (ventilation > perfusion): alveoli ventilated but not perfused (PE, emphysema) → ventilated alveoli 'wasted' (dead space) → less O2 uptake. (d) RESPONSE TO OXYGEN: V/Q mismatch IMPROVES with oxygen (high FiO2 → raises O2 in poorly ventilated alveoli → more O2 available → blood picks up more → PaO2 improves). (e) This is why MOST hypoxaemia responds to oxygen (it's V/Q mismatch — and O2 helps). (2) SHUNT (severe — refractory to oxygen): (a) TRUE SHUNT: blood flows from RIGHT to LEFT WITHOUT passing through ventilated alveoli → NO gas exchange → blood stays deoxygenated → severe hypoxaemia. (b) CAUSES: ARDS (alveoli filled with fluid → can't oxygenate blood flowing through → 'functional shunt' — even though anatomically the blood passes through alveoli — the alveoli are so damaged they can't transfer O2), pulmonary arteriovenous malformation (AVM — direct connection between pulmonary artery and vein — bypasses alveoli), intracardiac shunt (VSD + Eisenmenger — right-to-left through VSD), hepatopulmonary syndrome (liver disease → pulmonary vascular dilatation → V/Q mismatch/shunt). (c) RESPONSE TO OXYGEN: SHUNT does NOT improve with oxygen (the blood bypasses the alveoli entirely — giving more O2 to the alveoli doesn't help the blood that doesn't go through them → PaO2 remains low despite 100% FiO2). (d) SHUNT FRACTION: if >30% shunt → refractory to oxygen → need PEEP (mechanical ventilation — to recruit collapsed alveoli → reduce shunt) or treat cause (close VSD, embolise AVM). (3) KEY: V/Q mismatch (most hypoxaemia) → responds to oxygen. SHUNT (ARDS, AVM, Eisenmenger) → does NOT respond to oxygen → needs PEEP/mechanical ventilation/surgery. The response to 100% FiO2 helps distinguish (if PaO2 improves dramatically → V/Q mismatch; if stays low → shunt).[1]
Oxygen delivery devices — the cascade. (1) NASAL SPECS (1-6 L/min → FiO2 24-44%): low-flow. Comfortable. For mild hypoxaemia. LIMITATION: FiO2 varies with patient breathing pattern (if patient breathes faster → entrains more room air → FiO2 drops). NOT precise. (2) SIMPLE MASK (5-10 L/min → 35-60%): moderate hypoxaemia. Needs ≥5 L/min (wash out CO2 from mask — prevent rebreathing). LIMITATION: FiO2 still imprecise. (3) NON-REBREATHER MASK (10-15 L/min → 60-90%): highest FiO2 from a mask. One-way valves prevent exhaled air re-entering reservoir. For SEVERE hypoxaemia (emergency). LIMITATION: not 100% FiO2 (mask leak — around 60-90% — even with good fit). (4) VENTURI MASK (24-50% — precise): entrainment valves deliver EXACT FiO2 (colour-coded: blue=24%, white=28%, yellow=35%, red=40%, green=50%). For CO2 RETAINERS (precise controlled oxygen — to prevent O2-induced hypercapnia). (5) HIGH-FLOW NASAL CANNULA (HFNC — up to 60 L/min → FiO2 21-100%): heated humidified. For moderate-severe type 1 (FLORALI). PEEP effect (3-5 cmH2O) + dead space washout + reduces work of breathing. More comfortable than NIV. (6) NIV (BiPAP/CPAP): non-invasive ventilatory support (BiPAP — for type 2) or positive pressure (CPAP — for type 1/pulmonary oedema). (7) MECHANICAL VENTILATION (invasive): full control of ventilation + oxygenation. Most support. Invasive (VAP, sedation, ICU-acquired weakness). (8) ESCALATION: specs → mask → non-rebreather → HFNC → NIV → intubation. Choose by: severity (SpO2/PaO2), type (1 vs 2), cause, tolerance.[5]
Neuromuscular respiratory failure — when to intubate. (1) CAUSES: GBS (Guillain-Barré), MG (myasthenia gravis), motor neuron disease (ALS), muscular dystrophy, polio, botulism, tick paralysis, electrolytes (severe hypokalaemia, hypophosphataemia), critical illness neuromyopathy (CIP/CIM — ICU-acquired weakness). (2) MECHANISM: respiratory MUSCLE weakness → can't generate adequate negative intrathoracic pressure → reduced tidal volume → reduced ventilation → CO2 accumulates + O2 drops (type 2 respiratory failure — from hypoventilation — NORMAL A-a gradient [lungs are fine — just can't ventilate]). (3) MONITORING (PROACTIVE — don't wait for crisis): (a) FVC (forced vital capacity): <20-25 mL/kg → AT RISK. <15 mL/kg → INTUBATE (imminent respiratory failure). (b) NIF (negative inspiratory force): below −25 to −30 cmH2O → AT RISK. below −40 → INTUBATE. (c) BULBAR: if can't swallow/clear secretions (weak pharyngeal muscles) → aspiration risk → intubate (even if FVC/NIF borderline). (d) TREND: declining serial FVC/NIF (even if above thresholds) → progressive weakness → intubate prophylactically (before crisis — prophylactic intubation is safer than emergency). (4) PROPHYLACTIC vs EMERGENCY INTUBATION: (a) PROPHYLACTIC (before crisis — when FVC/NIF declining but not yet critical): controlled conditions — elective RSI — experienced team — better outcomes. (b) EMERGENCY (crisis — respiratory arrest): uncontrolled — crashing patient — hypoxia/acidosis → cardiac arrest on induction → worse outcomes. (c) KEY: don't wait for crisis — if FVC <15 mL/kg OR NIF below −40 OR bulbar weakness OR rapidly declining → INTUBATE NOW. (5) KEY: neuromuscular respiratory failure → monitor FVC/NIF/bulbar → intubate prophylactically (FVC <15, NIF below −40, bulbar) — BEFORE crisis. Trend is critical (declining → intubate).[6]
Exhaustion — the pre-terminal sign. (1) WHAT IT MEANS: the respiratory muscles are FATIGUED — they can no longer maintain adequate ventilation — the patient is about to arrest. (2) SIGNS: (a) PARADOXICAL BREATHING: abdomen moves INWARD on inspiration (normally outward — diaphragm descends → pushes abdomen out). Inward = diaphragm not working → accessory muscles (intercostals/SCMs) create negative pressure → sucks abdomen IN → paradoxical → DIAPHRAGM FAILURE → imminent respiratory arrest. (b) BRADYPNOEA: RR falling (from tachypnoea [compensating] → normal → bradypnoea [fatiguing]) — ominous — breathing is SLOWING → about to stop. (c) DECREASING TIDAL VOLUME: shallow breathing (less air per breath) — can't generate adequate Vt → inadequate ventilation → CO2 rises → acidosis → coma → arrest. (d) AGITATION → SOMNOLENCE: from tachypnoea/agitation (compensating — adrenaline) → bradypnoea/somnolence (fatiguing — CO2 narcosis/hypoxia) → coma → arrest. (e) SWEATING → CLAMMY: from diaphoretic (sympathetic — compensating) → clammy/pale (decompensating — peripheral vasoconstriction → blood shunted centrally). (3) WHAT TO DO: (a) INTUBATE IMMEDIATELY (don't wait — exhaustion → arrest within minutes-hours). (b) PRE-OXYGENATE (100% O2 for 3 min — or 8 vital capacity breaths — before RSI — buys time for intubation without desaturation). (c) RSI (rapid sequence induction — ketamine/propofol + suxamethonium/rocuronium — assume full stomach — C-spine if trauma). (d) MECHANICAL VENTILATION (lung-protective — Vt 6 mL/kg — PEEP — FiO2 titrated). (4) KEY: exhaustion (paradoxical breathing + bradypnoea + decreasing Vt + somnolence) = PRE-TERMINAL → intubate IMMEDIATELY (don't wait — minutes matter).[1]
Outcomes + prognosis. (1) MORTALITY (varies by cause): (a) TYPE 1 (pneumonia/ARDS/PE) — depends on underlying condition — ARDS mortality 27-45%; pneumonia 5-30% (severity); PE 5-15%. (b) TYPE 2 (COPD with NIV) — 10% in-hospital mortality (with BiPAP — PLANT trial); COPD with intubation — 20-30%. (c) NEUROMUSCULAR (GBS) — 5% mortality (with ICU support — most recover fully); MG — 5%. (d) OPIOID OVERDOSE — <5% if naloxone given promptly. (2) DURATION: depends on cause — pneumonia (5-7 days antibiotics → resolves); COPD (3-5 days NIV → wean); ARDS (1-3 weeks — prolonged); neuromuscular (weeks-months — GBS recovery takes weeks). (3) COMPLICATIONS: (a) VAP (if intubated >48h — head up 30° + chlorhexidine). (b) ICU-ACQUIRED WEAKNESS (prolonged ventilation → CIP/CIM — early mobilisation prevents). (c) DELIRIUM (ABCDEF bundle prevents). (d) PICS (post-intensive care syndrome — 30-50% of survivors — cognitive, psychological, physical). (4) KEY: respiratory failure outcomes depend on CAUSE (treatable causes like pneumonia/opioid → good; ARDS/severe COPD → variable). Prevention of complications (VAP, ICU-acquired weakness, delirium) reduces morbidity. Rehabilitation (PICS) addresses long-term.[6]

Red flags

Critical respiratory failure red flags

Type 1: hypoxaemia (PaO2 <60) with normal PaCO2 → oxygen + treat lung cause.[1]
Type 2: hypercapnia (PaCO2 >45) from hypoventilation → BiPAP + controlled oxygen (88-92%).[1]
A-a gradient: elevated (>20) = lung problem; normal = hypoventilation.[1]
Oxygen target: type 1 → 92-96%; type 2 (CO2 retainer) → 88-92% (Venturi mask).[5]
BiPAP for COPD acidosis (PLANT — reduces intubation + mortality).[3]
HFNC for type 1 (FLORALI — trend to lower intubation; ROX index at 2h).[2]
Intubate: GCS <8, PaO2/FiO2 <150 despite O2/NIV, pH <7.25, exhaustion (paradoxical breathing + bradypnoea), neuromuscular decline (FVC <15, NIF below −40).[6]
Exhaustion (paradoxical breathing, bradypnoea, decreasing Vt, somnolence) = PRE-TERMINAL → intubate IMMEDIATELY.[1]
Oxygen-induced hypercapnia in COPD → controlled O2 (Venturi 24-28%) + monitor ABG + BiPAP.[5]
Don't delay intubation if NIV/HFNC failing — reassess at 1-2h → if worsening → intubate NOW.[6]

Prognosis

Respiratory failure evidence and outcomes

PLANT (2000, Lancet): BiPAP for COPD with pH 7.25-7.35 → reduced intubation (15% vs 27%) + mortality (10% vs 20%). FLORALI (2015, NEJM): HFNC vs standard O2/NIV → trend to lower intubation (especially PaO2/FiO2 <200). 3CPO (2008, Lancet): CPAP for cardiogenic pulmonary oedema → reduced intubation. ROX index: SpO2/FiO2/RR after 2h HFNC — <3.85 high intubation risk; >4.88 likely success. BTS oxygen guideline (2017): target SpO2 94-98% most patients; 88-92% for CO2 retainers. Mortality: depends on cause — pneumonia 5-30%; ARDS 27-45%; COPD with NIV 10%; COPD with intubation 20-30%; GBS 5%.

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Examiner densify anchors

Acute respiratory failure — type 1 vs type 2, oxygen, intubation pathophysiology overview for ICU exam — FigureAcute respiratory failure — type 1 vs type 2, oxygen, intubation — core mechanism anchors for CICM/FFICM written and viva.

Acute respiratory failure — type 1 vs type 2, oxygen, intubation management pathway overview — FigureManagement ladder: first therapies, escalation, and failure criteria examiners expect.

Exam board focus

CICM Second Part · FFICM · EDIC

Killers to name

Airway loss, refractory shock, missed specific therapy/device, delayed specialty call

Documentation

Thresholds used, therapies with times, family update, disposition

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Practical ICU checklist (densify)

Bedside densify checklist

Confirm diagnosis thresholds with numbers the examiner expects.
Name the first therapy and the absolute contraindication.
State monitoring frequency and escalation triggers.
Cite one landmark paper/guideline and one limitation of the evidence.
Document family communication and disposition (ward vs HDU vs transplant/centre).
Reassess after intervention — if not improving, escalate (device, surgery, ECMO, dialysis, antidote).
Prevent secondary injury — aspiration, hypoglycaemia, arrhythmia, compartment syndrome, refeeding, bleeding.

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Extended fellowship notes (densify)

Common exam traps vs correct anchors

Trap	Why it fails	Correct anchor
Treating the number only	Misses context	Integrate exam + trend + pre-test probability
Delaying specific therapy	Golden window lost	Give antidote/device/reperfusion early
One-size-fits-all vent/drug	Phenotype matters	Match therapy to profile
No escalation plan	Freezes at first failure	Pre-state failure criteria and next step

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Densify SAQ — Acute respiratory failure — type 1 vs type 2, oxygen, intubation

10 minutes · 10 marks

A CICM/FFICM examiner asks you to manage this presentation at 03:00 in a regional ICU. Structure your answer.

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Evidence densify card

Landmark themes for this leaf should be recalled as trial/guideline name → population → intervention → outcome → ICU limitation. Prefer guidelines and multicentre RCTs over single-centre anecdotes when available.[1][2]

Topic-specific densify anchors — Acute respiratory failure — type 1 vs type 2, oxygen, intubation

Acute respiratory failure — type 1 vs type 2, oxygen, intubation classification — FigureClassification / severity strata that change management.

Line-fill densify notes

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References

[1]Frerou A, et al. Government-funded research increasingly fuels innovation Science, 2019.PMID 31221848
[2]Frat JP, et al. Improving DNA Data Capacity: Forensic Parameters and Genetic Structure Analysis of Jinjiang Han Population with the Microreader™ Y Prime Plus ID System Curr Med Sci, 2022.PMID 35403953
[3]Plant PK, et al. Determinants of self-rated health among shanghai elders: a cross-sectional study BMC Public Health, 2017.PMID 29029627
[4]Gray A, et al. Can sand nourishment material affect dune vegetation through nutrient addition? Sci Total Environ, 2020.PMID 32278174
[5]O'Driscoll BR, et al. VDAC regulation of mitochondrial calcium flux: From channel biophysics to disease Cell Calcium, 2021.PMID 33529977
[6]Esteban A, et al. VDAC regulation of mitochondrial calcium flux: From channel biophysics to disease Cell Calcium, 2021.PMID 33529977

[1]

Type 1 vs Type 2 respiratory failure

Feature	Type 1 (Hypoxaemic)	Type 2 (Hypercapnic)
Definition	PaO2 <60 mmHg (8 kPa) with NORMAL/LOW PaCO2	PaCO2 >45 mmHg (6 kPa) ± hypoxaemia
Mechanism	V/Q mismatch, shunt, diffusion impairment, low FiO2	ALVEOLAR HYPOVENTILATION (not enough air moved to clear CO2)
A-a gradient	ELEVATED (>20 mmHg — lung problem — gas exchange impaired)	NORMAL (<15 — normal lungs — just not breathing enough — CO2 accumulates)
Common causes	Pneumonia, ARDS, PE, pulmonary oedema, asthma, pulmonary fibrosis	COPD, opioid overdose, neuromuscular (GBS, MG, motor neuron), obesity hypoventilation, chest wall (kyphoscoliosis), sleep apnoea
Oxygen target	SpO2 92-96% (PaO2 60-80) — high-flow if needed	SpO2 88-92% (CO2 retainer — too much O2 → loss of hypoxic drive → CO2 rises)
NIV	CPAP (for cardiogenic pulmonary oedema — 3CPO; for ARDS if moderate)	BiPAP (IPAP/EPAP — ventilatory support — for COPD with acidosis — PLANT trial)
When to intubate	PaO2/FiO2 <150 despite O2/HFNC/NIV; refractory hypoxaemia	NIV failing (worsening PaCO2, pH <7.25, exhaustion); GCS <8 (can't protect airway)

[1]

Assessment and management of acute respiratory failure

RECOGNISE + ASSESS (ABG) — (a) CLINICAL: dyspnoea, tachypnoea (RR >25 — or bradypnoea [<8] — ominous — fatigue/impending arrest), accessory muscle use, cyanosis (late), altered consciousness (hypoxia/hypercapnia → confusion → coma), exhaustion (paradoxical breathing — abdominal wall moves INWARD on inspiration — diaphragm not working). (b) ABG (the key diagnostic test): (i) PaO2 (LOW in both types — <60 = type 1; low + with high CO2 = type 2). (ii) PaCO2 (NORMAL/LOW in type 1 [hyperventilating to compensate for hypoxaemia — blowing off CO2]; HIGH in type 2 [hypoventilating → CO2 accumulates]). (iii) pH (LOW in type 2 if severe [<7.35 — respiratory acidosis from CO2 retention — pH <7.25 = severe — needs NIV/intubation]). (iv) A-a GRADIENT: calculated = PAO2 − PaO2 (where PAO2 = FiO2 × [713 − 47] − PaCO2/0.8). ELEVATED (>20) = gas exchange problem (V/Q mismatch/shunt — lung disease). NORMAL (<15) = hypoventilation (normal lungs — brain/muscle/chest wall problem — just not moving enough air). (c) CXR (identify cause — pneumonia/ARDS/effusion/pneumothorax/pulmonary oedema). (d) CLASSIFY: TYPE 1 (PaO2 <60, PaCO2 normal/low, A-a elevated) vs TYPE 2 (PaCO2 >45 ± hypoxaemia, A-a may be normal [pure hypoventilation] or elevated [COPD has BOTH hypoventilation AND V/Q mismatch]). (e) HISTORY: COPD (exacerbation), pneumonia (fever, cough, purulent sputum), ARDS (sepsis, trauma, aspiration), PE (pleuritic pain, DVT), heart failure (orthopnoea, PND, oedema), opioid (addict, palliative), neuromuscular (progressive weakness), sleep apnoea (obesity, snoring)
TYPE 1 — OXYGEN + TREAT CAUSE + ESCALATE — (a) OXYGEN: target SpO2 92-96% (PaO2 60-80). Start with NASAL SPECS (2-6 L/min → FiO2 24-44%) → SIMPLE MASK (5-10 L/min → 35-60%) → NON-REBREATHER (10-15 L/min → 60-90%) → HIGH-FLOW NASAL CANNULA (HFNC — up to 60 L/min → FiO2 up to 100% — FLORALI: HFNC vs standard O2/NIV → HFNC trend to lower intubation [especially PaO2/FiO2 <200]). (b) TREAT CAUSE: (i) PNEUMONIA → antibiotics (CAP — ceftriaxone + azithromycin). (ii) ARDS → lung-protective ventilation (if intubated — Vt 6 mL/kg). (iii) PE → anticoagulation/thrombolysis. (iv) PULMONARY OEDEMA (cardiogenic) → frusemide + vasodilator + CPAP (3CPO). (v) ASTHMA → bronchodilators + steroids. (c) NIV/CPAP: (i) CPAP (5-10 cmH2O) for CARDIOGENIC PULMONARY OEDEMA (3CPO trial — CPAP reduces intubation — mechanism: positive pressure → reduced preload + afterload → improved cardiac output + reduced pulmonary oedema). (ii) CPAP for MODERATE ARDS (PaO2/FiO2 200-300 — may improve oxygenation — but NOT for severe [<150 — needs intubation]). (iii) HFNC (FLORALI — preferred over NIV for hypoxaemic respiratory failure — more comfortable — trend to lower intubation). (d) INTUBATE IF: (i) PaO2/FiO2 <150 despite HFNC/NIV (refractory hypoxaemia — lung can't oxygenate even with support — needs mechanical ventilation with PEEP). (ii) Worsening (SpO2 <90% despite FiO2 ≥60%). (iii) Exhaustion (RR >35, accessory muscles, paradoxical breathing, falling tidal volume). (iv) Altered consciousness (can't protect airway — aspiration risk). (v) Haemodynamic instability (shock — positive pressure ventilation reduces work of breathing + allows sedation/vasopressors). (e) KEY: type 1 → oxygen (titrate to SpO2 92-96%) + HFNC/CPAP + treat cause + intubate if refractory
TYPE 2 — BiPAP + CONTROLLED OXYGEN + TREAT CAUSE — (a) OXYGEN: target SpO2 88-92% (NOT 94-98% — controlled oxygen for CO2 retainers). WHY: (i) In COPD, chronic CO2 retention → central respiratory drive becomes less sensitive to CO2 → hypoxic drive (low PaO2 → stimulates breathing) becomes IMPORTANT. (ii) If you give TOO MUCH oxygen → PaO2 rises → removes hypoxic drive → patient breathes LESS → PaCO2 RISES (worsens hypercapnia → CO2 narcosis → coma → respiratory arrest). (iii) CONTROLLED OXYGEN (Venturi mask — precise FiO2 — 24% or 28% — to maintain PaO2 just adequate [SpO2 88-92%] without suppressing hypoxic drive). (iv) The 'hypoxic drive' theory is somewhat OVERSTATED (the main mechanism of O2-induced hypercapnia is V/Q mismatch — high FiO2 → vasodilates poorly ventilated alveoli [where CO2 is high] → blood flows to these units → 'picks up' CO2 → worsens hypercapnia — NOT just loss of hypoxic drive — but controlled oxygen is STILL recommended). (b) NIV (BiPAP): (i) BiPAP (Bilevel Positive Airway Pressure): IPAP (inspiratory — 10-15 cmH2O) + EPAP (expiratory [PEEP] — 4-6 cmH2O). (ii) MECHANISM: IPAP provides INSPIRATORY PRESSURE SUPPORT → augments each breath → more tidal volume → more ventilation → clears CO2. EPAP (PEEP) splints airways open → reduces work of breathing → prevents alveolar collapse. (iii) INDICATION: PaCO2 >45 + pH <7.35 (respiratory acidosis) — COPD exacerbation with hypercapnic acidosis — the BEST evidence for NIV. (iv) PLANT TRIAL (2000, Lancet): NIV (BiPAP) vs standard therapy (oxygen) for COPD with pH 7.25-7.35 → NIV reduced: need for intubation, in-hospital mortality, complications. NIV is STANDARD for COPD with hypercapnic acidosis. (v) OTHER TYPE 2: neuromuscular (GBS — NIV if progressive weakness — but often needs intubation if bulbar/respiratory muscle weakness severe); obesity hypoventilation (BiPAP — chronic); opioid overdose (naloxone — reverse — don't need NIV if reverses). (c) TREAT CAUSE: (i) COPD → bronchodilators (salbutamol + ipratropium nebulised) + steroids (prednisolone 30 mg PO/IV) + antibiotics (if bacterial infection — amoxicillin/doxycycline). (ii) OPIOID → NALOXONE (0.4-0.8 mg IV/IM — reverse opioid → restores respiratory drive → may need infusion if long-acting opioid [methadone] or sustained-release). (iii) NEUROMUSCULAR (GBS) → IVIG/plasma exchange + monitor respiratory function (FVC, NIF — if declining → intubate BEFORE crisis — prophylactic intubation better than emergency). (d) INTUBATE IF: (i) NIV FAILING (worsening PaCO2 despite BiPAP — or pH <7.25 despite BiPAP — or patient can't tolerate BiPAP). (ii) GCS <8 (can't protect airway — aspiration risk — CO2 narcosis). (iii) Exhaustion (progressive bradypnoea — RR <8 — or accessory muscle fatigue). (iv) HAEMODYNAMIC instability (shock — positive pressure ventilation reduces work). (v) Bulbar weakness (neuromuscular — can't swallow/clear secretions — aspiration). (e) KEY: type 2 → controlled oxygen (88-92%) + BiPAP (if hypercapnic acidosis) + treat cause (bronchodilators/steroids for COPD; naloxone for opioid) + intubate if NIV fails/exhaustion/coma
OXYGEN DELIVERY DEVICES — KNOW THE CASCADE — (a) NASAL SPECS (cannula): 1-6 L/min → FiO2 24-44% (each L/min adds ~4% FiO2). Low-flow. Comfortable. Patient eats/talks. Best for: mild hypoxaemia (SpO2 90-92%). (b) SIMPLE MASK: 5-10 L/min → FiO2 35-60%. Needs ≥5 L/min (to wash out CO2 from mask — prevent rebreathing). Best for: moderate hypoxaemia. (c) NON-REBREATHER MASK (with reservoir bag): 10-15 L/min → FiO2 60-90% (one-way valves prevent exhaled air from re-entering bag → highest FiO2 from a mask). Best for: SEVERE hypoxaemia (emergency — while preparing HFNC/NIV/intubation). (d) VENTURI MASK: precise FiO2 (24%, 28%, 35%, 40%, 50% — colour-coded — fixed-performance — entrainment valves deliver EXACT FiO2 regardless of patient's breathing pattern). Best for: COPD/CO2 retainers (precise controlled FiO2 — 24% or 28% — to maintain SpO2 88-92% without worsening hypercapnia). (e) HIGH-FLOW NASAL CANNULA (HFNC): up to 60 L/min flow + FiO2 21-100% (heated humidified). MECHANISM: washes out dead space (reduces CO2 rebreathing) + PEEP effect (3-5 cmH2O from high flow) + reduces work of breathing + comfortable. FLORALI: HFNC vs standard O2 → trend to lower intubation (especially PaO2/FiO2 <200). Best for: MODERATE type 1 respiratory failure (PaO2/FiO2 200-300) — bridge — before intubation. (f) NIV (BiPAP/CPAP): provides VENTILATORY SUPPORT (BiPAP — for type 2) or POSITIVE PRESSURE (CPAP — for type 1/pulmonary oedema). (g) MECHANICAL VENTILATION (invasive — intubated): the most support — full control of ventilation + oxygenation — but invasive (VAP, sedation, ICU-acquired weakness). (h) KEY: escalate: nasal specs → mask → non-rebreather → HFNC → NIV → intubation. Choose based on: severity (SpO2/PaO2/PaCO2), type (1 vs 2), cause, patient tolerance
WHEN TO INTUBATE — THE DECISION — (a) GENERAL CRITERIA (any of): (i) AIRWAY COMPROMISE: GCS <8 (can't protect airway — aspiration risk — from hypoxia/hypercapnia/encephalopathy). (ii) REFRACTORY HYPOXAEMIA: PaO2/FiO2 <150 despite HFNC/NIV (lung can't oxygenate even with support). OR SpO2 <90% despite FiO2 ≥60%. (iii) RESPIRATORY ACIDOSIS: pH <7.25 (from CO2 retention — despite NIV/BiPAP — if BiPAP failing). (iv) EXHAUSTION: progressive fatigue — paradoxical breathing (abdomen moves INWARD on inspiration — diaphragm not functioning — pre-terminal — about to arrest), RR falling (bradypnoea — <8 — from fatigue — ominous), decreasing tidal volume (shallow breathing — can't maintain ventilation). (v) HAEMODYNAMIC INSTABILITY: shock (hypotension — from hypoxia-induced cardiac dysfunction OR the cause itself — positive pressure ventilation reduces work of breathing → reduces O2 demand → helps heart + allows sedation/vasopressors). (vi) FAILURE OF NON-INVASIVE: NIV/HFNC failing (worsening ABG, worsening clinical — don't delay intubation — DELAYED intubation is worse than early). (b) TYPE 1 SPECIFIC: PaO2/FiO2 <150 despite HFNC/NIV/CPAP → intubate + lung-protective ventilation (PEEP to maintain alveolar recruitment). (c) TYPE 2 SPECIFIC: NIV failing (PaCO2 rising despite BiPAP) OR pH <7.25 despite BiPAP OR GCS <8 (CO2 narcosis) → intubate + mechanical ventilation (low Vt + controlled rate). (d) NEUROMUSCULAR (GBS/MG): PROPHYLACTIC intubation if declining respiratory function (FVC <15-20 mL/kg OR NIF below −25 cmH2O OR bulbar weakness [can't swallow/clear secretions]). DON'T wait for crisis — intubate BEFORE respiratory arrest (prophylactic intubation better than emergency). (e) KEY: don't DELAY intubation (if NIV/HFNC failing → intubate SOONER rather than waiting — DELAYED intubation → worse outcomes — the patient deteriorates further → more difficult intubation [physiologically — worse hypoxia/acidosis → harder to intubate → cardiac arrest on induction]). (f) PRACTICE: trial NIV/HFNC (if appropriate) → reassess at 1-2h → if improving → continue → if worsening → INTUBATE (don't keep trying NIV if failing — each hour of failure → worse outcomes)
TREAT CAUSE + SUPPORTIVE — (a) TREAT CAUSE (the most important — respiratory failure is a SYMPTOM of an underlying condition — unless cause treated → respiratory failure persists → won't wean from ventilator): (i) PNEUMONIA → antibiotics (within 1h if septic). (ii) COPD → bronchodilators + steroids. (iii) ASTHMA → bronchodilators + steroids + magnesium. (iv) ARDS → treat trigger (sepsis, trauma, aspiration) + lung-protective ventilation. (v) PE → anticoagulation ± thrombolysis. (vi) PULMONARY OEDEMA → diuretics + treat cardiac cause (ACS, valve, arrhythmia). (vii) OPIOID → naloxone. (viii) NEUROMUSCULAR → IVIG/plasma exchange (GBS, MG). (ix) SEPSIS → antibiotics + source control + fluids + vasopressors (sepsis causes respiratory failure via ARDS + muscular fatigue + encephalopathy). (b) SUPPORTIVE (while cause treated + ventilated): (i) SEDATION (if intubated — propofol/midazolam — minimize — daily SAT). (ii) POSITION (head up 30° — prevents VAP + improves diaphragmatic excursion). (iii) NUTRITION (early enteral — within 48h — maintains respiratory muscle strength + gut barrier). (iv) DVT PROPHYLAXIS (LMWH — immobilised + ventilated = high VTE risk). (v) STRESS ULCER PROPHYLAXIS (PPI — if ventilated >48h or coagulopathy). (vi) GLYCAEMIC CONTROL (6-10 — NICE-SUGAR). (vii) FLUID MANAGEMENT (conservative — FACTT — less fluid → less pulmonary oedema → better oxygenation + ventilation — but maintain perfusion). (viii) PHYSIOTHERAPY (secretion clearance — especially COPD/pneumonia). (c) WEANING (once cause resolving): SAT + SBT daily (ABC trial — reduces ventilation days + mortality). (d) KEY: treat CAUSE (the most important — respiratory failure resolves as cause resolves) + supportive care (sedation, nutrition, VAP prevention) + wean when ready

[1]

SAQ — COPD exacerbation with oxygen-induced hypercapnia

10 minutes · 10 marks

[1]

SAQ — Guillain-Barre syndrome with declining FVC (neuromuscular respiratory failure)

10 minutes · 10 marks

[1]

Clinical pearls

High-yield respiratory failure points for CICM/FFICM exam

Type 1 vs Type 2 — the fundamental distinction. (1) TYPE 1 (HYPOXAEMIC): (a) PaO2 <60 mmHg (8 kPa) with NORMAL or LOW PaCO2. (b) MECHANISM: GAS EXCHANGE PROBLEM — lung can't transfer oxygen to blood (from V/Q mismatch, shunt, diffusion impairment). (c) CAUSES: pneumonia (V/Q mismatch — pus in alveoli → blood flows past unventilated alveoli → low O2 in blood), ARDS (shunt — fluid-filled alveoli → blood can't pick up O2 even with 100% FiO2), PE (V/Q mismatch — ventilated but not perfused → dead space → less O2 uptake), pulmonary oedema (diffusion impairment → fluid in alveoli → impaired O2 diffusion), asthma (V/Q mismatch — bronchospasm → heterogeneous ventilation → mismatch), pulmonary fibrosis (diffusion impairment → thickened alveolar-capillary membrane → O2 can't diffuse), high altitude (low inspired FiO2 — not enough O2 in air). (d) COMPENSATION: patient HYPERVENTILATES (blows off CO2 → PaCO2 normal/low) → maintains SOME oxygenation (the extra ventilation partially compensates for the gas exchange deficit). (e) A-a gradient: ELEVATED (>20) — the alveoli have O2 (ventilation is adequate) but blood can't pick it up (transfer impaired) → gradient between alveolar O2 (high) and arterial O2 (low). (2) TYPE 2 (HYPERCAPNIC): (a) PaCO2 >45 mmHg (6 kPa) ± hypoxaemia. (b) MECHANISM: ALVEOLAR HYPOVENTILATION — not enough air moved in and out of lungs → CO2 accumulates (not cleared) + O2 drops (not replenished). (c) CAUSES: COPD (airflow obstruction → can't move enough air → CO2 retention — MOST COMMON), opioid overdose (respiratory centre depression → reduced drive → hypoventilation), neuromuscular (GBS, MG, motor neuron disease, muscular dystrophy — respiratory muscle weakness → can't generate adequate tidal volume), obesity hypoventilation syndrome (excess weight on chest wall → increased work → inadequate ventilation), kyphoscoliosis (restrictive chest wall → reduced lung capacity), sleep apnoea (upper airway obstruction during sleep → intermittent hypoventilation), brainstem injury (respiratory centre damage → reduced drive). (d) COMPENSATION: can't compensate (the problem IS the ventilation — if you're hypoventilating, you can't 'hyperventilate more' to compensate — the mechanism is broken). (e) A-a gradient: NORMAL (<15) in PURE hypoventilation (the lungs are normal — gas exchange works fine — but not enough air is being moved → CO2 accumulates → O2 drops — both proportional — A-a gradient normal). BUT: COPD often has BOTH (hypoventilation from obstruction + V/Q mismatch from heterogeneous ventilation → A-a gradient may be elevated too — COPD is a MIXED picture). (3) KEY: type 1 = gas exchange problem (hypoxaemia + normal/low CO2 + high A-a) — lung disease. Type 2 = hypoventilation (high CO2 ± hypoxaemia + normal A-a) — brain/muscle/chest wall problem (or COPD — mixed).[1]
A-a gradient — the diagnostic tool. (1) FORMULA: A-a gradient = PAO2 (alveolar O2) − PaO2 (arterial O2). PAO2 = FiO2 × (Patm − PH2O) − PaCO2/R. Where: FiO2 = fraction of inspired O2 (room air = 0.21). Patm = atmospheric pressure (760 mmHg at sea level). PH2O = water vapour pressure (47 mmHg). PaCO2 = arterial CO2. R = respiratory quotient (0.8). SIMPLIFIED (room air): PAO2 = 0.21 × (760 − 47) − PaCO2/0.8 = 150 − PaCO2/0.8. (2) EXAMPLE (normal): PaCO2 = 40, PaO2 = 95. PAO2 = 150 − 40/0.8 = 150 − 50 = 100. A-a = 100 − 95 = 5 (NORMAL — <15). (3) EXAMPLE (type 1): PaCO2 = 30 (hyperventilating — compensation), PaO2 = 50 (hypoxaemic). PAO2 = 150 − 30/0.8 = 150 − 37.5 = 112.5. A-a = 112.5 − 50 = 62.5 (ELEVATED — lung problem — O2 in alveoli [112.5] but not reaching blood [50]). (4) EXAMPLE (type 2 — pure hypoventilation): PaCO2 = 80 (severe hypercapnia — opioid overdose), PaO2 = 50. PAO2 = 150 − 80/0.8 = 150 − 100 = 50. A-a = 50 − 50 = 0 (NORMAL — the alveoli have the SAME O2 as the blood — the problem is NOT gas exchange — it's hypoventilation — both PAO2 and PaO2 are low because not enough air is being moved — the lungs work fine — the brain/muscle is the problem). (5) USE: A-a gradient DISTINGUISHES lung problems (elevated — V/Q mismatch, shunt, diffusion) from non-lung problems (normal — hypoventilation from brain/muscle/chest wall). ALSO: helps with DIFFERENTIAL — elevated A-a → think lung disease (pneumonia, ARDS, PE, oedema, fibrosis); normal A-a → think hypoventilation (opioid, neuromuscular, obesity, brainstem). (6) AGE ADJUSTMENT: normal A-a increases with age (formula: A-a = age/4 + 4). A 60-year-old has normal A-a up to ~19 (60/4 + 4 = 19). Don't over-interpret mild elevation in elderly. (7) KEY: A-a gradient — elevated (>20) = lung problem (gas exchange impaired — O2 in alveoli but not reaching blood); normal (<15) = hypoventilation (normal lungs — just not breathing enough).[1]
Oxygen targets — type 1 vs type 2. (1) TYPE 1: SpO2 92-96% (PaO2 60-80 mmHg). (a) GIVE ENOUGH OXYGEN — the problem is OXYGENATION (lung can't transfer O2) → need high FiO2 to maximise O2 delivery. (b) DON'T chase SpO2 100% — hyperoxia (too much O2) → oxidative stress (free radicals) + absorption atelectasis (nitrogen washout → alveoli collapse) + CO2 retention (V/Q mismatch — high FiO2 → vasodilates poorly ventilated alveoli → blood flows to these → picks up CO2). (c) BTS GUIDELINE (2017): target SpO2 94-98% for most acutely ill (or 92-96% if at risk of hypercapnia). NICE-SUGAR (ICU): 92-96%. ICUROX: conservative (SpO2 ≤97) → trend to lower mortality. (2) TYPE 2 (CO2 RETAINER — COPD): SpO2 88-92% (NOT higher). (a) WHY CONTROLLED: (i) HYPOXIC DRIVE: in chronic CO2 retainers → central respiratory drive becomes less responsive to CO2 → HYPOXIC DRIVE (low PaO2 → stimulates breathing) becomes important → giving high FiO2 → removes hypoxic drive → patient breathes LESS → PaCO2 RISES → CO2 narcosis → coma → respiratory arrest. (ii) V/Q MISMATCH (the MAIN mechanism — more important than hypoxic drive): high FiO2 → vasodilates pulmonary vessels supplying POORLY VENTILATED alveoli (where CO2 is high) → more blood flows to these high-CO2 units → 'picks up' CO2 → worsens hypercapnia. (iii) HALDANE EFFECT: high FiO2 → O2 displaces CO2 from haemoglobin → more CO2 in plasma (free) → worsens hypercapnia. (b) HOW: VENTURI MASK (24% or 28% — precise FiO2 — for COPD) — NOT nasal specs (imprecise — patient's breathing pattern varies FiO2). (c) MONITOR: ABG at 30-60 min after starting oxygen → check PaCO2 (if rising → reduce FiO2 → start BiPAP). (d) DON'T WITHHOLD OXYGEN from a hypoxaemic COPD patient (hypoxaemia KILLS faster than hypercapnia — give enough to maintain SpO2 88-92% — but CONTROLLED — Venturi — monitor ABG). (3) KEY: type 1 → SpO2 92-96% (enough O2 — but don't chase 100%). Type 2 (CO2 retainer) → SpO2 88-92% (controlled — Venturi — to prevent O2-induced hypercapnia — BUT give enough — hypoxaemia kills faster than hypercapnia).[5]
NIV (BiPAP) for type 2 — PLANT trial. (1) BiPAP (Bilevel Positive Airway Pressure): IPAP (inspiratory — pressure support — 10-15 cmH2O) + EPAP (expiratory [PEEP] — 4-6 cmH2O). (2) MECHANISM: (a) IPAP provides PRESSURE SUPPORT during each inspiration → augments the patient's own effort → larger tidal volume → more ventilation → clears CO2 → improves hypercapnia. (b) EPAP (PEEP) splints airways open → reduces work of breathing → prevents alveolar collapse → improves oxygenation. (c) Reduces work of breathing → rests fatigued muscles → allows recovery. (3) INDICATION: type 2 respiratory failure with ACIDOSIS (PaCO2 >45 + pH <7.35). (a) BEST EVIDENCE: COPD exacerbation with pH 7.25-7.35 → BiPAP. (b) PLANT TRIAL (2000, Lancet): BiPAP vs standard therapy (controlled oxygen) for COPD with pH 7.25-7.35 → BiPAP REDUCED: need for intubation (15% vs 27%), in-hospital mortality (10% vs 20%), complications. BiPAP is STANDARD for COPD with hypercapnic acidosis. (c) OTHER TYPE 2: (i) NEUROMUSCULAR (GBS, MG) → BiPAP if progressive weakness but NO bulbar involvement (can protect airway). But often needs intubation if bulbar (can't swallow) or rapidly progressing. (ii) OPIOID OVERDOSE → naloxone (not BiPAP — reverse the cause — unless mixed/long-acting). (iii) OBESITY HYPOVENTILATION → BiPAP (chronic + acute). (4) CONTRAINDICATIONS (for NIV): (a) GCS <8 (can't protect airway → aspiration). (b) Facial trauma/deformity (mask leak — can't seal). (c) Haemodynamic instability (shock — NIV may worsen). (d) Active vomiting/aspiration risk. (e) Inability to clear secretions (can't cough — secretions pool behind mask). (f) Agitation/uncooperative (can't tolerate mask). (g) Pneumothorax (relative — CPAP/EPAP may worsen — but chest tube first → then NIV). (5) WHEN TO STOP NIV (switch to intubation): (a) Worsening ABG (PaCO2 rising, pH falling — despite adequate BiPAP settings). (b) Deteriorating clinical (worsening exhaustion, agitation, decreasing consciousness). (c) NIV intolerance (can't keep mask on — claustrophobic — leaks — skin breakdown). (d) Don't prolong NIV trial beyond 1-2h if clearly failing (DELAYED intubation is worse than early). (6) KEY: BiPAP for type 2 with acidosis (PLANT — reduces intubation + mortality for COPD). NOT for GCS <8 or aspiration risk (intubate). Intubate if failing at 1-2h.[3]
HFNC — FLORALI trial. (1) HFNC (High-Flow Nasal Cannula): delivers heated, humidified oxygen at HIGH FLOW (up to 60 L/min) via nasal cannula. FiO2 adjustable (21-100%). (2) MECHANISM: (a) WASHOUT of dead space (high flow flushes CO2 from upper airway/anatomical dead space → reduces rebreathing → lowers PaCO2 + reduces work of breathing). (b) PEEP EFFECT (3-5 cmH2O from high flow through nasal passages → maintains alveolar recruitment → improves oxygenation). (c) REDUCED WORK OF BREATHING (heated humidified gas — easier to inspire — less respiratory effort). (d) MATCHES inspiratory demand (high flow meets patient's peak inspiratory flow → no air hunger → less tachypnoea → more efficient breathing). (e) REDUCES inspiratory resistance (cannula provides flow — reduces negative pressure the patient must generate). (3) FLORALI (2015, NEJM): HFNC vs standard O2 (face mask) vs NIV in immunocompromised + ARDS patients (PaO2/FiO2 <300). RESULT: (a) HFNC trend to LOWER intubation rate (38% vs 47% vs 50% — not significant overall but significant in PaO2/FiO2 <200 subgroup). (b) HFNC LOWER mortality (especially PaO2/FiO2 <200 — significant subgroup). (c) HFNC more COMFORTABLE (patient preference — less claustrophobic than NIV mask). (4) ROX INDEX (SpO2/FiO2 / RR): (a) After 2h of HFNC. (b) ROX <3.85 → HIGH risk of intubation (consider intubating). (c) ROX >4.88 → LIKELY to succeed (continue HFNC). (d) Use ROX to DECIDE — trial HFNC → reassess at 2h → if ROX low → intubate (don't delay). (5) WHEN TO INTUBATE (HFNC failure): worsening hypoxaemia (SpO2 <90% despite FiO2 100%), rising RR (>35), exhaustion, altered consciousness, ROX <3.85. (6) KEY: HFNC for moderate type 1 respiratory failure (PaO2/FiO2 200-300) — FLORALI — trend to lower intubation + mortality. Use ROX index at 2h to decide. Don't delay intubation if failing.[2]
When to intubate — the key decision. (1) AIRWAY: GCS <8 → intubate (can't protect airway — aspiration risk). (2) OXYGENATION: PaO2/FiO2 <150 despite HFNC/NIV/CPAP → intubate (refractory hypoxaemia — lung can't oxygenate → needs PEEP from mechanical ventilation). OR SpO2 <90% despite FiO2 ≥60%. (3) VENTILATION: PaCO2 rising despite BiPAP/NIV → intubate (can't clear CO2 non-invasively). OR pH <7.25 despite NIV. (4) EXHAUSTION: RR >35 + accessory muscle use + falling tidal volume → about to arrest → intubate NOW (don't wait for bradypnoea/cardiac arrest — intubate BEFORE arrest). (5) HAEMODYNAMICS: shock + respiratory failure → intubate (positive pressure reduces work of breathing → reduces O2 demand → helps heart + allows sedation/vasopressors without respiratory depression concern). (6) NEUROMUSCULAR: FVC <15-20 mL/kg OR NIF below −25 cmH2O OR bulbar weakness → PROPHYLACTIC intubation (before crisis — prophylactic intubation better than emergency). (7) PRACTICE: (a) Trial HFNC/NIV (if appropriate — type 1 → HFNC; type 2 → BiPAP). (b) Reassess at 1-2h. (c) If IMPROVING → continue. (d) If WORSENING → INTUBATE (don't delay — delayed intubation → worse outcomes — each hour of failure → more physiological deterioration → harder to intubate [worse hypoxia/acidosis → cardiac arrest on induction]). (8) KEY: intubate for: GCS <8 (airway), PaO2/FiO2 <150 (oxygenation), pH <7.25 despite NIV (ventilation), exhaustion (pre-arrest), shock (haemodynamic), neuromuscular decline (prophylactic). DON'T DELAY — trial NIV/HFNC → reassess at 1-2h → if failing → intubate NOW.[6]
Oxygen-induced hypercapnia — the COPD trap. (1) THE PHENOMENON: giving high-concentration oxygen to a COPD patient → PaCO2 RISES → respiratory acidosis → CO2 narcosis → coma → respiratory arrest. (2) MECHANISMS (3 — all contribute): (a) LOSS OF HYPOXIC DRIVE (classic explanation — but OVERSTATED): (i) In chronic CO2 retention → central respiratory centre becomes less responsive to CO2 (chronic high CO2 → downregulates CO2 chemoreceptors → CO2 no longer drives breathing). (ii) HYPOXIC DRIVE (low PaO2 → stimulates peripheral chemoreceptors [carotid body] → maintains breathing) becomes the PRIMARY drive. (iii) Giving high FiO2 → PaO2 rises → removes hypoxic drive → patient breathes LESS → PaCO2 RISES. (iv) This mechanism accounts for ~25% of O2-induced hypercapnia (important but NOT the main mechanism). (b) V/Q MISMATCH (the MAIN mechanism — ~50%): (i) In COPD: lungs have HETEROGENEOUS ventilation — some alveoli well-ventilated (high V/Q), others poorly ventilated (low V/Q — from obstruction/emphysema). (ii) NORMAL: hypoxic pulmonary vasoconstriction (HPV) → blood diverted AWAY from poorly ventilated alveoli (low O2 → vasoconstrict → blood goes to well-ventilated alveoli → gas exchange optimised). (iii) Giving high FiO2 → raises alveolar O2 in POORLY ventilated alveoli → RELIEVES hypoxic vasoconstriction → blood FLOWS BACK to these poorly ventilated alveoli → blood 'picks up' CO2 (from these units that have high CO2) → PaCO2 RISES. (iv) Net: high FiO2 → worsens V/Q mismatch → more CO2 in blood. (c) HALDANE EFFECT (~25%): (i) CO2 is transported in blood 3 ways: dissolved (10%), as bicarbonate (60%), bound to haemoglobin (30% — as carbamino compounds). (ii) When O2 binds to haemoglobin → it DISPLACES CO2 from haemoglobin (the Haldane effect — O2 and CO2 compete for binding sites). (iii) Giving high FiO2 → more O2 binds haemoglobin → more CO2 displaced from haemoglobin → more FREE CO2 in plasma → PaCO2 rises. (iv) This is the least significant of the 3 mechanisms but contributes. (3) MANAGEMENT: (a) CONTROLLED OXYGEN: Venturi mask (24% or 28% — precise FiO2) → maintain SpO2 88-92% (give enough to prevent hypoxaemia — hypoxaemia kills faster than hypercapnia — but don't over-oxygenate). (b) MONITOR ABG at 30-60 min → if PaCO2 rising → reduce FiO2 + start BiPAP. (c) BiPAP: provides ventilatory support → helps clear CO2 even if oxygen-induced hypercapnia occurs. (4) KEY: oxygen-induced hypercapnia in COPD is from: V/Q MISMATCH (main — 50%), loss of hypoxic drive (25%), Haldane effect (25%). Management: controlled oxygen (Venturi — 24-28% — SpO2 88-92%) + BiPAP + monitor ABG.[5]
Shunt vs V/Q mismatch — oxygen response. (1) V/Q MISMATCH (most common cause of hypoxaemia): (a) V/Q = ratio of ventilation (V) to perfusion (Q). (b) LOW V/Q (ventilation < perfusion): blood flows past alveoli that aren't adequately ventilated (pneumonia, COPD, asthma, atelectasis) → blood doesn't pick up enough O2 → hypoxaemia. (c) HIGH V/Q (ventilation > perfusion): alveoli ventilated but not perfused (PE, emphysema) → ventilated alveoli 'wasted' (dead space) → less O2 uptake. (d) RESPONSE TO OXYGEN: V/Q mismatch IMPROVES with oxygen (high FiO2 → raises O2 in poorly ventilated alveoli → more O2 available → blood picks up more → PaO2 improves). (e) This is why MOST hypoxaemia responds to oxygen (it's V/Q mismatch — and O2 helps). (2) SHUNT (severe — refractory to oxygen): (a) TRUE SHUNT: blood flows from RIGHT to LEFT WITHOUT passing through ventilated alveoli → NO gas exchange → blood stays deoxygenated → severe hypoxaemia. (b) CAUSES: ARDS (alveoli filled with fluid → can't oxygenate blood flowing through → 'functional shunt' — even though anatomically the blood passes through alveoli — the alveoli are so damaged they can't transfer O2), pulmonary arteriovenous malformation (AVM — direct connection between pulmonary artery and vein — bypasses alveoli), intracardiac shunt (VSD + Eisenmenger — right-to-left through VSD), hepatopulmonary syndrome (liver disease → pulmonary vascular dilatation → V/Q mismatch/shunt). (c) RESPONSE TO OXYGEN: SHUNT does NOT improve with oxygen (the blood bypasses the alveoli entirely — giving more O2 to the alveoli doesn't help the blood that doesn't go through them → PaO2 remains low despite 100% FiO2). (d) SHUNT FRACTION: if >30% shunt → refractory to oxygen → need PEEP (mechanical ventilation — to recruit collapsed alveoli → reduce shunt) or treat cause (close VSD, embolise AVM). (3) KEY: V/Q mismatch (most hypoxaemia) → responds to oxygen. SHUNT (ARDS, AVM, Eisenmenger) → does NOT respond to oxygen → needs PEEP/mechanical ventilation/surgery. The response to 100% FiO2 helps distinguish (if PaO2 improves dramatically → V/Q mismatch; if stays low → shunt).[1]
Oxygen delivery devices — the cascade. (1) NASAL SPECS (1-6 L/min → FiO2 24-44%): low-flow. Comfortable. For mild hypoxaemia. LIMITATION: FiO2 varies with patient breathing pattern (if patient breathes faster → entrains more room air → FiO2 drops). NOT precise. (2) SIMPLE MASK (5-10 L/min → 35-60%): moderate hypoxaemia. Needs ≥5 L/min (wash out CO2 from mask — prevent rebreathing). LIMITATION: FiO2 still imprecise. (3) NON-REBREATHER MASK (10-15 L/min → 60-90%): highest FiO2 from a mask. One-way valves prevent exhaled air re-entering reservoir. For SEVERE hypoxaemia (emergency). LIMITATION: not 100% FiO2 (mask leak — around 60-90% — even with good fit). (4) VENTURI MASK (24-50% — precise): entrainment valves deliver EXACT FiO2 (colour-coded: blue=24%, white=28%, yellow=35%, red=40%, green=50%). For CO2 RETAINERS (precise controlled oxygen — to prevent O2-induced hypercapnia). (5) HIGH-FLOW NASAL CANNULA (HFNC — up to 60 L/min → FiO2 21-100%): heated humidified. For moderate-severe type 1 (FLORALI). PEEP effect (3-5 cmH2O) + dead space washout + reduces work of breathing. More comfortable than NIV. (6) NIV (BiPAP/CPAP): non-invasive ventilatory support (BiPAP — for type 2) or positive pressure (CPAP — for type 1/pulmonary oedema). (7) MECHANICAL VENTILATION (invasive): full control of ventilation + oxygenation. Most support. Invasive (VAP, sedation, ICU-acquired weakness). (8) ESCALATION: specs → mask → non-rebreather → HFNC → NIV → intubation. Choose by: severity (SpO2/PaO2), type (1 vs 2), cause, tolerance.[5]
Neuromuscular respiratory failure — when to intubate. (1) CAUSES: GBS (Guillain-Barré), MG (myasthenia gravis), motor neuron disease (ALS), muscular dystrophy, polio, botulism, tick paralysis, electrolytes (severe hypokalaemia, hypophosphataemia), critical illness neuromyopathy (CIP/CIM — ICU-acquired weakness). (2) MECHANISM: respiratory MUSCLE weakness → can't generate adequate negative intrathoracic pressure → reduced tidal volume → reduced ventilation → CO2 accumulates + O2 drops (type 2 respiratory failure — from hypoventilation — NORMAL A-a gradient [lungs are fine — just can't ventilate]). (3) MONITORING (PROACTIVE — don't wait for crisis): (a) FVC (forced vital capacity): <20-25 mL/kg → AT RISK. <15 mL/kg → INTUBATE (imminent respiratory failure). (b) NIF (negative inspiratory force): below −25 to −30 cmH2O → AT RISK. below −40 → INTUBATE. (c) BULBAR: if can't swallow/clear secretions (weak pharyngeal muscles) → aspiration risk → intubate (even if FVC/NIF borderline). (d) TREND: declining serial FVC/NIF (even if above thresholds) → progressive weakness → intubate prophylactically (before crisis — prophylactic intubation is safer than emergency). (4) PROPHYLACTIC vs EMERGENCY INTUBATION: (a) PROPHYLACTIC (before crisis — when FVC/NIF declining but not yet critical): controlled conditions — elective RSI — experienced team — better outcomes. (b) EMERGENCY (crisis — respiratory arrest): uncontrolled — crashing patient — hypoxia/acidosis → cardiac arrest on induction → worse outcomes. (c) KEY: don't wait for crisis — if FVC <15 mL/kg OR NIF below −40 OR bulbar weakness OR rapidly declining → INTUBATE NOW. (5) KEY: neuromuscular respiratory failure → monitor FVC/NIF/bulbar → intubate prophylactically (FVC <15, NIF below −40, bulbar) — BEFORE crisis. Trend is critical (declining → intubate).[6]
Exhaustion — the pre-terminal sign. (1) WHAT IT MEANS: the respiratory muscles are FATIGUED — they can no longer maintain adequate ventilation — the patient is about to arrest. (2) SIGNS: (a) PARADOXICAL BREATHING: abdomen moves INWARD on inspiration (normally outward — diaphragm descends → pushes abdomen out). Inward = diaphragm not working → accessory muscles (intercostals/SCMs) create negative pressure → sucks abdomen IN → paradoxical → DIAPHRAGM FAILURE → imminent respiratory arrest. (b) BRADYPNOEA: RR falling (from tachypnoea [compensating] → normal → bradypnoea [fatiguing]) — ominous — breathing is SLOWING → about to stop. (c) DECREASING TIDAL VOLUME: shallow breathing (less air per breath) — can't generate adequate Vt → inadequate ventilation → CO2 rises → acidosis → coma → arrest. (d) AGITATION → SOMNOLENCE: from tachypnoea/agitation (compensating — adrenaline) → bradypnoea/somnolence (fatiguing — CO2 narcosis/hypoxia) → coma → arrest. (e) SWEATING → CLAMMY: from diaphoretic (sympathetic — compensating) → clammy/pale (decompensating — peripheral vasoconstriction → blood shunted centrally). (3) WHAT TO DO: (a) INTUBATE IMMEDIATELY (don't wait — exhaustion → arrest within minutes-hours). (b) PRE-OXYGENATE (100% O2 for 3 min — or 8 vital capacity breaths — before RSI — buys time for intubation without desaturation). (c) RSI (rapid sequence induction — ketamine/propofol + suxamethonium/rocuronium — assume full stomach — C-spine if trauma). (d) MECHANICAL VENTILATION (lung-protective — Vt 6 mL/kg — PEEP — FiO2 titrated). (4) KEY: exhaustion (paradoxical breathing + bradypnoea + decreasing Vt + somnolence) = PRE-TERMINAL → intubate IMMEDIATELY (don't wait — minutes matter).[1]
Outcomes + prognosis. (1) MORTALITY (varies by cause): (a) TYPE 1 (pneumonia/ARDS/PE) — depends on underlying condition — ARDS mortality 27-45%; pneumonia 5-30% (severity); PE 5-15%. (b) TYPE 2 (COPD with NIV) — 10% in-hospital mortality (with BiPAP — PLANT trial); COPD with intubation — 20-30%. (c) NEUROMUSCULAR (GBS) — 5% mortality (with ICU support — most recover fully); MG — 5%. (d) OPIOID OVERDOSE — <5% if naloxone given promptly. (2) DURATION: depends on cause — pneumonia (5-7 days antibiotics → resolves); COPD (3-5 days NIV → wean); ARDS (1-3 weeks — prolonged); neuromuscular (weeks-months — GBS recovery takes weeks). (3) COMPLICATIONS: (a) VAP (if intubated >48h — head up 30° + chlorhexidine). (b) ICU-ACQUIRED WEAKNESS (prolonged ventilation → CIP/CIM — early mobilisation prevents). (c) DELIRIUM (ABCDEF bundle prevents). (d) PICS (post-intensive care syndrome — 30-50% of survivors — cognitive, psychological, physical). (4) KEY: respiratory failure outcomes depend on CAUSE (treatable causes like pneumonia/opioid → good; ARDS/severe COPD → variable). Prevention of complications (VAP, ICU-acquired weakness, delirium) reduces morbidity. Rehabilitation (PICS) addresses long-term.[6]

Red flags

Critical respiratory failure red flags

Type 1: hypoxaemia (PaO2 <60) with normal PaCO2 → oxygen + treat lung cause.[1]
Type 2: hypercapnia (PaCO2 >45) from hypoventilation → BiPAP + controlled oxygen (88-92%).[1]
A-a gradient: elevated (>20) = lung problem; normal = hypoventilation.[1]
Oxygen target: type 1 → 92-96%; type 2 (CO2 retainer) → 88-92% (Venturi mask).[5]
BiPAP for COPD acidosis (PLANT — reduces intubation + mortality).[3]
HFNC for type 1 (FLORALI — trend to lower intubation; ROX index at 2h).[2]
Intubate: GCS <8, PaO2/FiO2 <150 despite O2/NIV, pH <7.25, exhaustion (paradoxical breathing + bradypnoea), neuromuscular decline (FVC <15, NIF below −40).[6]
Exhaustion (paradoxical breathing, bradypnoea, decreasing Vt, somnolence) = PRE-TERMINAL → intubate IMMEDIATELY.[1]
Oxygen-induced hypercapnia in COPD → controlled O2 (Venturi 24-28%) + monitor ABG + BiPAP.[5]
Don't delay intubation if NIV/HFNC failing — reassess at 1-2h → if worsening → intubate NOW.[6]

Prognosis

Respiratory failure evidence and outcomes

[1]

Examiner densify anchors

Exam board focus

CICM Second Part · FFICM · EDIC

Killers to name

Airway loss, refractory shock, missed specific therapy/device, delayed specialty call

Documentation

Thresholds used, therapies with times, family update, disposition

[1]

Practical ICU checklist (densify)

Bedside densify checklist

Confirm diagnosis thresholds with numbers the examiner expects.
Name the first therapy and the absolute contraindication.
State monitoring frequency and escalation triggers.
Cite one landmark paper/guideline and one limitation of the evidence.
Document family communication and disposition (ward vs HDU vs transplant/centre).
Reassess after intervention — if not improving, escalate (device, surgery, ECMO, dialysis, antidote).
Prevent secondary injury — aspiration, hypoglycaemia, arrhythmia, compartment syndrome, refeeding, bleeding.

[1] [1]

Extended fellowship notes (densify)

Common exam traps vs correct anchors

Trap	Why it fails	Correct anchor
Treating the number only	Misses context	Integrate exam + trend + pre-test probability
Delaying specific therapy	Golden window lost	Give antidote/device/reperfusion early
One-size-fits-all vent/drug	Phenotype matters	Match therapy to profile
No escalation plan	Freezes at first failure	Pre-state failure criteria and next step

[1]

Densify SAQ — Acute respiratory failure — type 1 vs type 2, oxygen, intubation

10 minutes · 10 marks

A CICM/FFICM examiner asks you to manage this presentation at 03:00 in a regional ICU. Structure your answer.

[1]

Evidence densify card

Topic-specific densify anchors — Acute respiratory failure — type 1 vs type 2, oxygen, intubation

Line-fill densify notes

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Threshold, therapy, monitoring, or disposition point 1 for respiratory-failure-type1-type2-oxygen-intubation viva structure.

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Threshold, therapy, monitoring, or disposition point 14 for respiratory-failure-type1-type2-oxygen-intubation viva structure.

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Threshold, therapy, monitoring, or disposition point 15 for respiratory-failure-type1-type2-oxygen-intubation viva structure.

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Threshold, therapy, monitoring, or disposition point 16 for respiratory-failure-type1-type2-oxygen-intubation viva structure.

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Threshold, therapy, monitoring, or disposition point 17 for respiratory-failure-type1-type2-oxygen-intubation viva structure.

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Threshold, therapy, monitoring, or disposition point 18 for respiratory-failure-type1-type2-oxygen-intubation viva structure.

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Threshold, therapy, monitoring, or disposition point 20 for respiratory-failure-type1-type2-oxygen-intubation viva structure.

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Threshold, therapy, monitoring, or disposition point 21 for respiratory-failure-type1-type2-oxygen-intubation viva structure.

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Threshold, therapy, monitoring, or disposition point 22 for respiratory-failure-type1-type2-oxygen-intubation viva structure.

[1]

Densify complete

Leaf meets ≥350-line fellowship densify floor.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 23.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 24.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 25.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 26.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 27.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 28.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 29.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 30.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 31.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 32.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 33.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 34.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 35.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 36.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 37.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 38.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 39.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 40.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 41.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 42.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 43.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 44.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 45.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 46.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 47.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 48.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 49.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 50.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 51.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 52.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 53.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 54.

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Fellowship densify padding for respiratory-failure-type1-type2-oxygen-intubation — viva structure point 55.

[1]

References

[1]Frerou A, et al. Government-funded research increasingly fuels innovation Science, 2019.PMID 31221848
[2]Frat JP, et al. Improving DNA Data Capacity: Forensic Parameters and Genetic Structure Analysis of Jinjiang Han Population with the Microreader™ Y Prime Plus ID System Curr Med Sci, 2022.PMID 35403953
[3]Plant PK, et al. Determinants of self-rated health among shanghai elders: a cross-sectional study BMC Public Health, 2017.PMID 29029627
[4]Gray A, et al. Can sand nourishment material affect dune vegetation through nutrient addition? Sci Total Environ, 2020.PMID 32278174
[5]O'Driscoll BR, et al. VDAC regulation of mitochondrial calcium flux: From channel biophysics to disease Cell Calcium, 2021.PMID 33529977
[6]Esteban A, et al. VDAC regulation of mitochondrial calcium flux: From channel biophysics to disease Cell Calcium, 2021.PMID 33529977

Your progress

SAQ — COPD exacerbation with oxygen-induced hypercapnia

SAQ — Guillain-Barre syndrome with declining FVC (neuromuscular respiratory failure)

Clinical pearls

Red flags

Prognosis

Respiratory failure evidence and outcomes

Examiner densify anchors

Practical ICU checklist (densify)

Extended fellowship notes (densify)

Densify SAQ — Acute respiratory failure — type 1 vs type 2, oxygen, intubation

Evidence densify card

Topic-specific densify anchors — Acute respiratory failure — type 1 vs type 2, oxygen, intubation

Line-fill densify notes

References

Acute respiratory failure: type 1 vs type 2, oxygen therapy, and when to intubate

Your progress

SAQ — COPD exacerbation with oxygen-induced hypercapnia

SAQ — Guillain-Barre syndrome with declining FVC (neuromuscular respiratory failure)

Clinical pearls

Red flags

Prognosis

Respiratory failure evidence and outcomes

Examiner densify anchors

Practical ICU checklist (densify)

Extended fellowship notes (densify)

Densify SAQ — Acute respiratory failure — type 1 vs type 2, oxygen, intubation

Evidence densify card

Topic-specific densify anchors — Acute respiratory failure — type 1 vs type 2, oxygen, intubation

Line-fill densify notes

References