Acute severe asthma in the ICU (status asthmaticus) · ICU Topics

Cinematic ICU scene of a young adult in severe status asthmaticus with accessory muscle use, continuous nebulised salbutamol running through the in-line circuit, an IV magnesium syringe on a pump, a ventilator waveform showing a shark-fin pressure trace with expiratory flow failing to reach baseline, clinical-blue lighting, no faces, no text — FigureStatus asthmaticus — escalate the bronchodilators, give IV magnesium 2 g, and ventilate with permissive hypercapnia (small tidal volume, low rate, long expiration) if the patient tires. A silent chest, a normal or rising PaCO2, and bradycardia are pre-arrest signs — intubate now.

Severity assessment

Accurate stratification drives disposition and the decision to intubate. The principle that unifies every marker below is simple: asthma normally causes HYPOcapnia and respiratory alkalosis (the patient hyperventilates to compensate for hypoxaemia and the hypoxic ventilatory drive). Loss of that hypocapnia — a "normal" PaCO2 — means the patient is fatiguing, and a rising PaCO2 means imminent respiratory arrest. This single gas observation is the most heavily examined concept in acute asthma.[1]

Clinical signs by severity tier

Acute asthma severity (BTS/SIGN) — full clinical profile

Parameter	Moderate	Acute severe	Life-threatening	Near-fatal
PEF (% predicted/best)	50-75%	33-50%	<33%	— (intubated)
Speech	Full sentences	Cannot complete sentences	Words / cannot speak	—
Respiratory rate	<25	>25	Exhaustion / slow	—
Heart rate	<110	>110	Tachy → bradycardia	Variable
SpO2	92-94%	<92%	<92% on O2	—
PaCO2	Low (<4.5 kPa)	Low (hyperventilating)	NORMAL or RISING	RISING (permitted)
Chest auscultation	Wheeze ± accessory use	Wheeze, accessory muscles	SILENT CHEST (no air movement)	—
Other	—	—	Cyanosis, altered GCS, exhaustion, hypotension	Rising PaCO2 needing ventilation
Disposition	Ward / discharge	HDU / resus	ICU — prepare for intubation	ICU ventilated

[1]

Asthma severity in ICU (click each)

Any ONE: SpO2 <92%, silent chest, cyanosis, exhaustion, bradycardia, hypotension, altered GCS, normal/rising PaCO2, PF <33%

Mortality Moderate-high

MEDICAL EMERGENCY. Continuous nebulised bronchodilators, IV magnesium 2g, IV steroids, high-flow oxygen. Prepare for intubation if deteriorating. ICU admission.

[1] [2]

Key assessment modalities

How to assess the deteriorating asthmatic

Peak expiratory flow (PEF)

Most useful single objective measure if the patient can perform it. Compare to the patient's PERSONAL BEST (not just predicted — best captures their baseline). <33% best/predicted = life-threatening. Re-check after each bronchodilator cycle to chart trajectory. CANNOT perform PEF in the exhausted patient = itself a danger sign.

Oxygen saturation + arterial blood gas

SpO2 <92% on air = severe; <92% on supplemental O2 = life-threatening. ALWAYS take an arterial gas in acute severe asthma — the PaCO2 trajectory is the key. Low PaCO2 (respiratory alkalosis) = reassuring; normal PaCO2 = fatigue; rising PaCO2 = pre-arrest. Expect initial respiratory alkalosis; a NORMAL pH with normal/high CO2 is the warning.

Speech and posture

Ability to count to ten on one breath (~complete a sentence) tracks airflow. Words only = life-threatening. Sitting upright, leaning forward on arms (tripod), accessory muscle use, and intercostal recession indicate high work of breathing. Agitation and diaphoresis reflect hypoxaemia and hypercapnia.

Examination: wheeze is NOT severity

Wheeze reflects turbulent flow through narrowed airways — its LOUDNESS does not correlate with severity. The DANGER is the SILENT CHEST (no wheeze = no air movement). Reassessing wheeze that then disappears may mean improvement OR terminal fatigue — use PEF/gas, not auscultation alone, to distinguish.

Chest X-ray (after stabilisation)

Not routine — only to exclude differential/complications: pneumothorax (asymmetric hyperresonance, sudden deterioration), mucus plugging with lobar collapse, pneumomediastinum (subcutaneous emphysema), aspiration, or pneumonia. Do not delay treatment for a CXR.

[1]

Risk factors for fatal asthma (recognise and flag early)

Prior events

Strongest predictors

Previous near-fatal asthma (ICU/intubation/arest)
≥2 ED visits or ≥1 admission in the last 12 months
Sudden-onset (Type 2) rather than slow-onset attacks

Treatment & adherence

Modifiable

Over-reliance on SABA (≥3 canisters/year) — marker of poor control
Poor ICS adherence or no maintenance preventer
Non-attendance at asthma review
Food allergy (anaphylaxis–asthma overlap)

Psychosocial

Often missed

Psychiatric illness, depression, substance misuse
Low socioeconomic status, employment/housing instability
Adolescence / young adult — risk-taking, denial
Learning difficulty or poor health literacy

[1]

Pathophysiology

Educational schematic of status asthmaticus: bronchoconstriction, mucosal oedema, mucus plugging, dynamic hyperinflation with auto-PEEP, V/Q mismatch and rising PaCO2 — FigureStatus asthmaticus pathophysiology — severe airflow obstruction produces dynamic hyperinflation and auto-PEEP. Rising PaCO2, silent chest, and exhaustion mark life-threatening failure.

Status asthmaticus is the end-result of three overlapping processes that, unlike a routine exacerbation, become self-sustaining: [1]

Bronchial smooth muscle spasm — the acute, reversible component; the target of bronchodilators.
Airway inflammation — mucosal oedema, eosinophilic/neutrophilic infiltrate, epithelial denudation; the target of corticosteroids (hours to work).
Mucus plugging — tenacious, inspissated secretions and Casts occluding small and medium airways; largely refractory to bronchodilators and the dominant finding at autopsy in fatal asthma. [1]

The dangerous mechanical consequence is critical small-airway narrowing producing a high respiratory time constant (resistance × compliance). Expiration cannot complete before the next inspiration arrives, so each breath stacks on the last (dynamic hyperinflation). Alveolar pressure rises, the lungs over-distend, and the intrathoracic pressure transmitted to the heart and great vessels obstructs venous return and compresses the right ventricle — producing the characteristic preload-dependent hypotension that resolves the instant the ventilator is disconnected.[2]

Two pathophysiological phenotypes behave very differently and the distinction is examinable: [1]

Asthma phenotypes in status asthmaticus

Feature	Type 1 — slow-onset (eosinophilic)	Type 2 — sudden-onset (neutrophilic / asphyxic)
Onset	Hours-days of worsening	Minutes-hours
Trigger	Viral infection, allergen drift, non-adherence	Allergen/irritant bolus, exercise, stress, anaphylaxis
Dominant mechanism	Inflammation + oedema + mucus	Massive bronchospasm
Inflammatory cell	Eosinophil (T2-high)	Neutrophil (T2-low)
Demographic	Adults, chronic severe asthma	Younger, sensitised patients
Gas at presentation	Often already hypoxaemic/hypercapnic	Often near-arrest at first contact
Response to steroids	Good	Limited (steroids need hours)
Mortality pattern	Slow deterioration, arrest if untreated	Rapid asphyxia before therapy can act

[1]

Status asthmaticus — why the numbers matter

Intrinsic PEEP target

auto-PEEP >0 means air is trapped

1:3–1:4

I:E ratio in ventilation

long expiration is the safety mechanism

~5–10%

Mortality (intubated)

mostly from dynamic hyperinflation → arrest

80–90%

ECMO survival in asthma

reversible disease — best of any ECMO indication

ICU management — the full ladder

Escalation ladder for status asthmaticus: controlled oxygen, continuous nebulised salbutamol and ipratropium, systemic steroids, IV magnesium, ketamine induction, protective ventilation with long expiratory time, ECMO rescue — FigureEscalation ladder — continuous neb bronchodilators, early steroids, IV magnesium 2 g, then controlled intubation with ketamine and a low-rate long-TE strategy; call ECMO early for refractory gas exchange.

[1]

Initial resuscitation and first-line therapy

Status asthmaticus ICU protocol

Oxygen + continuous bronchodilators

High-flow oxygen (target SpO2 94-98%). Continuous nebulised salbutamol 5-10 mg/h + ipratropium 500 mcg every 4-6h. Do NOT stop salbutamol for heart rate alone (tachycardia is expected and tolerated). Monitor K+ (salbutamol causes hypokalaemia).

IV magnesium sulphate

Magnesium sulphate 2 g IV over 20 min (not bolus — can cause hypotension). Mechanism: inhibits calcium influx into bronchial smooth muscle → bronchodilation. Effective in acute severe asthma. Repeat dose may be given. Monitor for hypotension, areflexia (magnesium toxicity).

Systemic corticosteroids

Hydrocortisone 100 mg IV (or prednisolone 40-60 mg PO if tolerating oral). Take 6-12h to work (gene transcription effect). Give early — do NOT wait to see if bronchodilators alone work. Continue for 5 days. Equivalent oral/IV efficacy — use IV if cannot tolerate oral.

IV bronchodilators (if refractory)

IV salbutamol infusion (5-15 mcg/min — monitor for tachycardia, hypokalaemia, lactic acidosis). IV aminophylline (5 mg/kg loading over 20 min, then 0.5 mg/kg/h infusion — monitor levels, side effects: arrhythmia, seizures, nausea). IV magnesium already given. Consider IV ketamine (bronchodilator + anaesthetic — useful for intubation).

Ventilation strategy (if intubation required)

PERMISSIVE HYPERCAPNIA. Ketamine induction (bronchodilator). Rocuronium (NOT suxamethonium — risk of bradycardia/asystole with high-dose beta-2 agonists). Settings: small tidal volume 6 mL/kg PBW, LOW respiratory rate 10-12/min, LONG expiratory time (I:E 1:3 or 1:4), PEEP 0-5 (minimise — high PEEP worsens hyperinflation). Accept PaCO2 up to 80-100 mmHg if pH >7.15.

Avoid dynamic hyperinflation

Dynamic hyperinflation = trapped air cannot be exhaled before next breath → lungs overinflate → compresses heart and great vessels → hypotension → cardiac arrest. SIGNS: hypotension at end-inspiration, improvement when ventilator disconnected (allowing exhalation). PREVENT: low RR, small Vt, long expiration. If hypotension with ventilation: DISCONNECT briefly, let patient exhale, then resume at lower RR/Vt.

Last-line therapies

Volatile anaesthetics (sevoflurane, isoflurane via anaesthetic machine) — potent bronchodilators. ECMO (VV-ECMO) for refractory cases as bridge to recovery. Heliox (helium-oxygen mixture — lower density, reduces turbulent flow and work of breathing) — may help before intubation. Bronchoscopy to remove mucus plugs.

[1] [2]

The pharmacological ladder (exam-must-know depth)

Bronchodilators treat the spasm; corticosteroids treat the inflammation; neither addresses mucus plugging (which is why ventilation may still be needed). Steroids take 6-12 h to act — give them early and in parallel with bronchodilators, never sequentially. [1]

Pharmacological ladder for status asthmaticus

Step	Drug	Dose / route	Mechanism	Key cautions
1	Oxygen	High-flow, titrate SpO2 94-98%	Treats hypoxaemia; ↓hypoxic drive	Don't hyperoxia — CO2 retention rare in asthma vs COPD
2a	Salbutamol (SABA)	5 mg NEB q15-20 min or continuous 5-10 mg/h	β2-agonist → ↑cAMP → bronchial SM relaxation	Hypokalaemia (shifts K⁺ into cells), lactic acidosis (↑glycolysis), tremor, tachycardia — do NOT stop for HR alone
2b	Ipratropium bromide (SAMA)	500 mcg NEB q4-6h (combine with salbutamol)	Muscarinic antagonist → ↓cGMP → bronchodilation; additive with β2	Less effective alone; benefit is in combination. Dry mouth, urinary retention in elderly
3	Systemic corticosteroid	Prednisolone 40-60 mg PO or hydrocortisone 100 mg IV q6h. Oral = IV efficacy	Genome effects: ↑anti-inflammatory genes, ↓cytokines/transcription. 6-12 h onset	Give EARLY. Hyperglycaemia, mood effects. 5-7 day course, no taper if <14 days
4	IV magnesium sulphate	2 g (8 mmol) over 20 min; may repeat q4-6h	Ca²⁺ antagonist on bronchial SM; inhibits ACh release; mast-cell stabilisation	Hypotension, flushing, hyporeflexia. Not as a bolus. Watch if pre-existing heart block
5	IV salbutamol infusion	250 mcg over 10 min load → 5-20 mcg/min	As above but systemic delivery reaches obstructed airways	Tachyarrhythmia, severe hypokalaemia, lactate ↑. Reserve for poor inhaled delivery
5b	IV ketamine	1-2 mg/kg bolus, then 0.5-1 mg/kg/h infusion (if intubated)	NMDA antagonist; ↑sympathetic tone → bronchodilation; ideal induction + sedation agent	Hypertension, tachycardia, emergence phenomena, hypersalivation (co-administer antisialagogue)
6	Aminophylline (methylxanthine)	5 mg/kg load over 20 min → 0.5 mg/kg/h	PDE inhibitor → ↑cAMP; weak bronchodilator	Narrow therapeutic window: arrhythmia, seizures, nausea. Check levels. CYP1A2 interactions. Many guidelines now advise against starting acutely
7	Volatile anaesthetics	Sevoflurane / isoflurane 1-2% via anaesthetic machine	Direct bronchial SM relaxation (β2-independent); blunt airway reflexes; sedation	Hypotension, arrhythmia, need scavenging, malignant hyperthermia risk. Needs anaesthetic machine/vaporiser
8	Heliox	70:30 or 80:20 He:O2 by facemask	↓Density → laminar flow → ↓resistance & work of breathing	Max FiO2 only 30-40% — fails if severe hypoxaemia; most ICU ventilators uncalibrated for He
9	VV-ECMO	Cannula → membrane oxygenator → return	Bypasses lungs → rest the lung → no hyperinflation	Bleeding, thrombosis, resource-intensive. Survival 80-90% in asthma

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Steroids — oral vs IV, and timing

Oral prednisolone 40-60 mg is equivalent in efficacy to IV hydrocortisone provided the patient can swallow and absorb. Use IV if vomiting, intubated, or in extremis.[1]
Onset is 6-12 hours (genomic mechanism); effect peaks at 24-48 h. Give immediately alongside the first bronchodilator — do not wait to "see if salbutamol works".
5-7 day course; no taper needed for courses <14 days. Steroids reduce relapse after the acute attack.
Consider adding ICS (inhaled corticosteroid) early in recovery to rebuild preventer therapy and reduce re-admission.

IV magnesium — mechanism, evidence, dosing

Mechanism: Mg²⁺ is a calcium-channel antagonist at bronchial smooth muscle (competitively inhibits Ca²⁺ influx), inhibits acetylcholine release at the neuromuscular junction, and stabilises mast cells — collectively producing bronchodilation independent of the β2 pathway.[1]

Dose: 2 g (8 mmol) in 100 mL over 20 minutes (faster causes hypotension; a true bolus is contraindicated). Repeat doses every 4-6 h are reasonable in refractory cases; monitor reflexes. [1]

Evidence — the MAGNETIC and 3Mg trials are the landmark studies: [1]

2013

MAGNETIC

Lancet Respir Med 2013

508 children (2-16 y), severe asthma — nebulised MgSO4 vs placebo, added to salbutamol+ipratropium

Key finding

Nebulised Mg improved Yung Asthma Severity Score only in the more severe subgroup; modest benefit overall, no significant harm

Practice change

Nebulised Mg considered in children with severe attacks not responding to first-line therapy

2013

3Mg

Lancet Respir Med 2013

1109 adults with severe acute asthma — IV MgSO4 vs nebulised MgSO4 vs placebo, added to standard care

Key finding

IV Mg did NOT significantly reduce admissions overall (trend to benefit); nebulised Mg had no clear role in adults. Benefit concentrated in the most severe subset.

Practice change

IV Mg reserved for severe attacks failing standard therapy; not routine in all acute asthma

[1]

Magnesium in acute asthma — pragmatic use

2 g

IV dose

over 20 min, not bolus

~15%

Admission reduction

meta-analysis, severe subgroup

20 min

Infusion time

faster → hypotension

4-6 h

Repeat interval

monitor reflexes and BP

[1]

Aminophylline / methylxanthines — downgraded

GINA and BTS/SIGN do not recommend starting aminophylline or theophylline routinely in acute asthma. The Cochrane meta-analysis found no clear benefit over β2-agonists, with a narrow therapeutic window (toxicity: nausea, seizures, supraventricular and ventricular arrhythmia) and significant CYP1A2 drug interactions. Exceptions: a patient already on maintenance theophylline (check level — may be subtherapeutic) and the rare refractory case under specialist guidance. Do not start acutely as a reflex.[1]

Non-invasive ventilation (BiPAP) in asthma

NIV in acute asthma is controversial and adjunctive, not standard. Unlike COPD (where BiPAP is first-line for hypercapnic exacerbation), asthma is fundamentally a low-CO2 / high-drive disease — the patient who becomes hypercapnic is near-arrest and usually needs intubation, not a mask. NIV's theoretical role is to reduce the work of breathing and improve aerosolised drug delivery in the tiring but not yet failing patient, buying time for steroids to act.[8]

When to consider NIV

Acute severe asthma, rising work of breathing, paCO2 still normal or low (not yet hypercapnic).
Patient cooperative and able to protect airway.
As a bridge while waiting for steroids/Mg to work — not as a substitute for intubation in the clearly failing patient.
Contraindicated if: altered consciousness, inability to clear secretions, haemodynamic instability, vomiting/bowel obstruction, facial trauma, or a rising PaCO2 with fatigue (these mandate intubation). [1]

Practical BiPAP settings in asthma

BiPAP setup for acute asthma (if used)

Mode and interface

BiPAP (spontaneous/timed). Full face mask initially (least leak, best in respiratory distress); switch to nasal once improving. Continuous SpO2, ECG, and ideally serial gases (NIV + asthma can mask deterioration).

Pressure settings

Start LOW to avoid hyperinflation: IPAP 8-10 cmH2O, EPAP 4-5 cmH2O (ΔP 4-6 cmH2O to augment tidal volume). Titrate IPAP up slowly to a max ~15 cmH2O guided by effort and gas exchange. Keep EPAP LOW — extrinsic PEEP stacks on intrinsic PEEP and worsens hyperinflation.

FiO2

Titrate to SpO2 94-98% (attach O2 to mask port). Lower density of He-O2 not reliably delivered via standard BiPAP circuits.

Nebulised bronchodilators through NIV

Place the nebuliser in the circuit (between the Y-piece and mask) — ventilatory airflow actually IMPROVES drug delivery to obstructed airways. Continue salbutamol 5 mg q1h + ipratropium 500 mcg q6h.

Re-assess at 30-60 min — strict stop criteria

IMPROVING (↓RR, ↓accessory use, ↓PaCO2 if it was raised): continue. STATIC or WORSENING (rising PaCO2, falling pH, exhaustion, silent chest): STOP NIV, intubate. Do not let NIV delay definitive airway management — that delay is the trap.

[8] [1]

Mechanical ventilation strategy

The single governing principle: the ventilator cannot cure asthma; it can only keep the patient alive while bronchodilators and steroids act. Your job is to avoid dynamic hyperinflation at all costs — even at the price of severe hypercapnia. Over-ventilating to "normalise" CO2 is the classic and fatal mistake.[2][5]

Indications for intubation

Absolute

Intubate now

Cardiac or respiratory arrest
Reduced GCS / inability to protect airway (CO2 narcosis)
Apnoea / agonal breathing

Relative

Intubate early

Exhaustion (paradoxical breathing, silent chest)
Rising PaCO2 with falling pH despite maximal therapy
Refractory hypoxaemia (SpO2 <90% on high-flow O2)
Haemodynamic instability (hypotension, bradycardia)
Failure of NIV trial

Intubation pharmacology

Drugs and technique for the asthmatic intubation

Preoxygenation

100% O2 for 3 min (or 8 vital-capacity breaths). Asthmatics desaturate FAST — low FRC, high O2 consumption from the work of breathing, and V/Q mismatch. Have a backup airway plan and a senior operator.

Induction — KETAMINE preferred

Ketamine 1-2 mg/kg IV. It is a BRONCHODILATOR (increases catecholamine release → β2 effect on airway SM) AND maintains BP (sympathetic stimulation). AVOID propofol (vasodilation + histamine → bronchospasm + hypotension) and thiopental (histamine → bronchospasm).

Paralysis — rocuronium

Rocuronium 1.2 mg/kg (intubating dose). Cautions around suxamethonium: rare reports of bradycardia/asystole in patients loaded with β2-agonists; sux is acceptable but rocuronium avoids this and provides a longer window. Avoid prolonged paralysis (ICU-acquired weakness; combine with myopathy in asthma).

Largest practical ETT

Use the largest ETT that fits (8.0-8.5 in adults). Narrower tubes increase resistance (Poiseuille: resistance ∝ 1/radius⁴), which matters because you will deliver bronchodilators through the tube and will need to suction thick secretions.

Avoid awake / fibreoptic intubation

Stimulation of an already-reactive airway can trigger further bronchospasm. RSI is standard. If anticipated difficult airway, have an experienced operator and a supraglottic-airway/surgical backup.

[2]

Initial ventilator settings — "low and slow, long expiratory"

Initial ventilator settings for ventilated status asthmaticus

Setting	Recommended	Rationale
Mode	Volume-controlled (VC) preferred	Guarantees delivered Vt; easier to monitor plateau pressure and detect hyperinflation
Tidal volume	6 mL/kg PBW (down to 4 if needed)	Less volume to exhale → less hyperinflation. Use predicted/ideal, not actual weight
Respiratory rate	10-12 /min (down to 8)	Slow rate → long expiratory time → complete emptying
Inspiratory flow	High (60-100 L/min) with square (decelerating OFF) waveform	Short inspiratory time → maximises expiratory time
I:E ratio	1:3 to 1:4 (1:5 in severe)	Long expiration is the safety mechanism
PEEP	0-5 cmH2O (often 0 initially)	Minimise — extrinsic PEEP adds to intrinsic PEEP. Set ≈ 80% of measured intrinsic PEEP if you must use it
FiO2	100% initially, titrate to SpO2 94-98%	Wean as gas exchange improves
Plateau pressure	<30 cmH2O (an end-inspiratory hold)	Surrogate for dynamic hyperinflation; >30 = reduce Vt/RR

[1]

Setting up the ventilator — step by step

Calculate PBW

Male: 50 + 0.91 × (height cm − 152.4). Female: 45.5 + 0.91 × (height cm − 152.4). Never use actual body weight — Vt is a proxy for lung size which tracks with height.

Set low Vt and low RR

Vt 6 mL/kg PBW. RR 10-12 (start 10 if very severe). The product — minute ventilation — is deliberately LOW; this is what permits long expiration.

Shorten inspiratory time

High inspiratory flow (60-100 L/min) with a constant-flow (square) waveform keeps Ti short. The ventilator's expiratory time is then maximised (Ti short + low rate = long Te).

Target I:E 1:3 or longer

Most modern ventilators display I:E. If it is 1:2 or shorter, your RR is too high or inspiratory flow too low — fix that before doing anything else.

Set low PEEP

PEEP 0 (or up to 5). The obstructed airway already has high INTRINSIC PEEP (auto-PEEP) — adding extrinsic PEEP can be additive and worsen hyperinflation. (In COPD you match PEEPi to splint airways; in asthma the trapped gas is the problem — be more conservative.)

Sedate deeply ± paralyse (early)

Patient-ventilator asynchrony drives up minute ventilation and worsens bronchospasm. Deep sedation (propofol ± opioid, or a KETAMINE infusion for its bronchodilator effect) is essential. Short-acting cisatracurium for the first 24-48 h if dyssynchronous — but watch for critical-illness myopathy, especially with concomitant steroids.

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Monitoring for dynamic hyperinflation (auto-PEEP) — the killer

The defining danger of ventilated asthma. Auto-PEEP (intrinsic PEEP) is the positive end-expiratory pressure generated by trapped gas that has not fully exited before the next breath.[2]

How to measure intrinsic (auto-)PEEP:

End-expiratory hold (expiratory pause): occlude the expiratory port at end-expiration; the pressure equilibrates to the trapped-gas pressure = intrinsic PEEP. Normal is ~0; >5 cmH2O is significant, >10 is dangerous.
Plateau pressure (end-inspiratory hold): 0.5 s inspiratory pause; reflects peak alveolar pressure. Keep <30 cmH2O. A high Pplat in asthma = hyperinflation, NOT a target to chase. [1]

Clinical signs of dynamic hyperinflation:

Hypotension that worsens with each inspiration and improves dramatically when the ventilator is disconnected (the pathognomonic test).
High Pplat (>30), high auto-PEEP, slow expiratory flow that does not return to baseline before the next breath.
Rising CVP with inspiration (transmitted intrathoracic pressure). [1]

Treatment — the disconnection manoeuvre: [1]

Dynamic hyperinflation emergency response

Recognise

New hypotension shortly after starting/increasing ventilation, especially with high Pplat or auto-PEEP, OR unexplained hypotension/tachycardia in a ventilated asthmatic.

DISCONNECT the circuit

Manually allow the patient to fully exhale (squeeze the chest gently if needed). Listen for a prolonged whoosh of escaping gas. Watch the blood pressure rise over 10-30 seconds — confirmation of dynamic hyperinflation.

Reduce minute ventilation

Reconnect at a LOWER respiratory rate (8-10), LOWER Vt (4-5 mL/kg if needed), and ensure a LONGER expiratory time (higher inspiratory flow, I:E 1:4-1:5).

Deepen sedation ± paralyse

Eliminate patient-ventilator dyssynchrony (double-triggering, breath-stacking) which is often the precipitant.

Escalate bronchodilation

Continuous nebulised salbutamol through the circuit, ± IV salbutamol, ± repeat IV magnesium. Consider ketamine infusion (bronchodilation + sedation). If still refractory → volatile anaesthetic / VV-ECMO.

[1] [1]

The historical basis for permissive hypercapnia is Darioli & Perret (1984), who reported zero mortality in 26 mechanically ventilated status asthmaticus patients using controlled hypoventilation — a paradigm shift away from the aggressive normocapnic ventilation that had produced mortality of 10-30%. The principle survives unchanged.[5]

Severe cases may need helium-oxygen (Heliox)

Heliox is a helium-oxygen mixture (usually 70:30 or 80:20). Helium is less dense than nitrogen, so for any given airway geometry the flow is less turbulent (lower Reynolds number) — improving flow and reducing the work of breathing, particularly through the large/medium airways where turbulence dominates.[9]

Practical role in asthma:

Most useful pre-intubation in the spontaneously breathing patient with high work of breathing, to buy time for bronchodilators/steroids.
Theoretical role in ventilated severe asthma — but most ICU ventilators are not calibrated for helium, so delivered Vt and flows are inaccurate (a serious safety issue). Only use on a ventilator validated for Heliox with experienced staff.
Limitation: maximum FiO2 is only 30-40% — fails in severe hypoxaemia.
Evidence: Cochrane systematic review shows no consistent outcome benefit; use as a temporising adjunct, not a standard therapy. [1]

Refractory bronchospasm — escalation beyond standard ventilation

Volatile anaesthetic agents

Inhaled sevoflurane, isoflurane, and desflurane are potent bronchodilators — they relax airway smooth muscle by a mechanism independent of β2 receptors (direct effect on smooth muscle, and suppression of airway reflexes). In refractory status asthmaticus unresponsive to continuous β2-agonists, magnesium, and steroids, volatiles can break bronchospasm within minutes.[2]

Practical issues (these are the exam answers):

Require an anaesthetic machine with a vaporiser — most ICU ventilators do not deliver inhaled anaesthetics (dedicated ICU anaesthetic devices now exist; check local availability).
Need gas scavenging for staff and environmental safety (occupational exposure limits).
Hypotension from vasodilation is common — may need vasopressor support.
Sensitise the myocardium to catecholamines (arrhythmia risk).
Contraindicated in malignant hyperthermia susceptibility.
Evidence is case series/reports only (no RCTs feasible) but the effect is dramatic and widely accepted as a last-line salvage therapy. [1]

VV-ECMO for near-fatal asthma

VV-ECMO is the ultimate rescue. The rationale is powerful: asthma is reversible — bronchospasm and inflammation resolve over hours-days with steroids — so ECMO needs only to bridge the patient to recovery, allowing the ventilator to be set to complete "rest" (very low rate, very low Vt, eliminating hyperinflation entirely).[6]

Indications (case-by-case at an ECMO centre):

Refractory hypoxaemia or life-threatening acidosis (pH <7.1) despite optimised ventilation, volatile anaesthetics, and full bronchodilation.
Inability to control dynamic hyperinflation/pneumothorax with conventional ventilation.
Early cannulation — do not wait for cardiac arrest (then consider VA-ECMO/ECPR). [1]

Outcomes — striking: [1]

VV-ECMO in near-fatal asthma — outcomes

80-90%

Survival to discharge

best of any adult ECMO indication

Hours-days

Typical run

short — bridge to recovery

Lower

Complication rate

vs other ECMO indications

Reversible

Underlying disease

why outcomes are so good

The 80-90% survival figure comes from the ESO/ELSO registry and case series; asthma has the best ECMO survival of any adult indication precisely because the disease is self-limiting.[6]

Other adjuncts

Bronchoscopy: for radiographic lobar collapse from mucus plugging — removes tenacious casts unresponsive to bronchodilation. Use cautiously in a tenuous ventilated patient.
Mucolytics (N-acetylcysteine, rhDNAse): limited evidence; may help mucus plugging but can provoke bronchospasm — use cautiously.
Treat the trigger: antibiotics only if bacterial infection (most exacerbations are viral); stop culprit drugs (β-blockers, NSAIDs in sensitive patients, cholinesterase inhibitors). [1]

Complications

Complications of severe asthma and its ventilation

Complication	Mechanism	Recognition	Action
Dynamic hyperinflation → arrest	Breath-stacking compresses great vessels	Hypotension ↑with inspiration, ↓on disconnection	DISCONNECT, ↓RR, ↓Vt, deepen sedation
Tension pneumothorax	Alveolar rupture from high pressure	Unilateral signs + hypotension, ↑Pplat	Immediate needle decompression → chest drain
Pneumomediastinum / SQ emphysema	Alveolar rupture tracking centrally	Subcutaneous crepitus, CXR	Usually self-limiting; exclude pneumothorax
Critical-illness myopathy (CIM)	Steroids + NMB + sepsis	Flaccid weakness, failed wean	Minimise NMB duration; early PT
Hypokalaemia	β2 agonists shift K⁺ into cells	ECG (T-wave changes, ectopics)	Replace K⁺; monitor with continuous nebs
Lactic acidosis	β2-driven aerobic glycolysis	↑Lactate, normal ScvO2	Do not over-treat; ↓bronchodilator once improving
Atelectasis / mucus plugging	Tenacious secretions	Lobar collapse on CXR	Physiotherapy, bronchoscopy, hydration
Aspiration	Reduced GCS / post-extubation	New infiltrate, fever	Antibiotics, lung-protective ventilation

[1]

Prognosis

Outcomes in status asthmaticus

5-10%

Mortality if intubated

mostly dynamic hyperinflation → arrest

~80-90%

ECMO survival

best of any adult ECMO indication

~4%

Pneumothorax rate

ventilated asthma — higher with high Pplat

Hours-days

ECMO run length

bridge to recovery (disease is reversible)

Prognosis is driven by avoiding the preventable killers: dynamic hyperinflation (the dominant cause of ventilated-asthma death), pneumothorax, and delayed intubation. With permissive hypercapnia, early bronchodilation, and ECMO for the truly refractory, mortality has fallen from the 10-30% of the normocapnic era to single digits. Long-term, survivors need a written asthma action plan, preventer therapy optimisation (ICS ± biologic for T2-severe asthma), trigger avoidance, and follow-up to prevent recurrence — a near-fatal attack is the strongest predictor of a future fatal one.[1]

Exam practice

SAQ — Near-fatal asthma ventilation

10 minutes · 10 marks

A 28-year-old woman with known asthma presents with 2 days of worsening wheeze and breathlessness despite her usual inhalers. She is agitated, speaking single words, RR 32, SpO2 88% on 15 L/min via NRM, HR 132, BP 148/92, chest almost silent on auscultation. ABG: pH 7.18, PaCO2 7.8 kPa (59 mmHg), PaO2 7.5 kPa (56 mmHg), HCO3 24, lactate 3.4. PEF 90 L/min (best 480).

[1]

Clinical pearls

High-yield status asthmaticus points for the CICM/FFICM exam

Silent chest = no air movement — pre-arrest sign. Intubate NOW.[1]
Normal/rising PaCO2 in asthma = life-threatening (should be low from hyperventilation). The single most examined gas concept.[1]
IV magnesium 2g over 20min — bronchodilator by Ca²⁺ antagonism. Give in acute severe asthma. Not as a bolus (hypotension).[1]
Permissive hypercapnia when ventilating: small Vt, low RR, long expiration. Accept PaCO2 to 10-13 kPa if pH >7.15.[2]
Dynamic hyperinflation = main danger of mechanical ventilation → hypotension → arrest. The "disconnect test" is diagnostic and therapeutic.[2]
If hypotension during ventilation: DISCONNECT — let patient exhale, then resume at lower RR/Vt and longer I:E.[2]
Ketamine for intubation — bronchodilator + maintains BP. Avoid propofol/thiopental (histamine, hypotension).[2]
Salbutamol causes hypokalaemia — monitor and replace K⁺ (shifts into cells via β2-Na/K pump).[1]
Lactic acidosis from β2 agonists is type B (aerobic glycolysis) — do NOT confuse with worsening asthma or sepsis.[1]
Volatile anaesthetics (sevoflurane/isoflurane) — potent last-line bronchodilator, β2-independent. Need scavenging + anaesthetic machine.[2]
Heliox — lower density → laminar flow → less work of breathing. Best pre-intubation; max FiO2 only 30-40%.[9]
Aminophylline — NOT recommended routinely (narrow therapeutic window, no benefit over β2). Check levels if patient already on it.[1]
Bradycardia + hypotension in asthma = pre-arrest — prepare for intubation.[1]
Risk factors for fatal asthma: previous near-fatal episode, recent ED visit, SABA over-reliance (≥3 canisters/yr), poor adherence, psychosocial issues.[1]
Plateau pressure <30 cmH2O and auto-PEEP ≈ 0 are the two ventilator targets; high values mean hyperinflation regardless of what the SpO2 shows.[2]
Oral prednisolone = IV hydrocortisone in efficacy — give PO if the patient can swallow; give early (6-12 h to act).[1]
I:E ratio 1:3-1:4 is the signature of asthma ventilation — long expiration is the safety mechanism. If you see 1:2, your rate is too high or inspiratory flow too low.[2]
NIV (BiPAP) in asthma is a bridge, not a destination — only with serial gases and a pre-agreed threshold to abandon and intubate. The trap is NIV masking deterioration.[8]
VV-ECMO for refractory near-fatal asthma: 80-90% survival — the best of any adult ECMO indication, because asthma is reversible. Refer early.[6]
Darioli & Perret (1984) established controlled hypoventilation (permissive hypercapnia) with zero mortality in 26 ventilated asthmatics — the historical pivot away from fatal normocapnic ventilation.[5]
Two phenotypes behave differently: Type 1 (slow, eosinophilic, steroid-responsive) vs Type 2 (sudden, neutrophilic, asphyxic) — sudden-onset arrests before therapy can act.[1]
Pneumothorax in ventilated asthma: unilateral signs + hypotension = tension until proven otherwise — needle decompress, then chest drain. High Pplat is the risk factor.[2]
Critical-illness myopathy (CIM): the triad of steroids + NMB + severe asthma is high-risk — minimise NMB duration, mobilise early.[2]
Mucus plugging is the pathology least responsive to bronchodilators — it is why some patients still need ventilation despite full medical therapy. Bronchoscopy if lobar collapse.[2]

Red flags

Critical status asthmaticus red flags

Silent chest = NO AIR MOVEMENT — pre-arrest sign. Intubate NOW.[1]
Normal/rising PaCO2 in asthma = life-threatening. Should be LOW from hyperventilation.[1]
PERMISSIVE HYPERCAPNIA when ventilating. Small Vt, low RR, long expiration (I:E 1:3-1:4).[2]
Dynamic hyperinflation = the #1 killer. Hypotension on ventilation → DISCONNECT, let exhale, resume at lower settings.[2]
Bradycardia/hypotension = pre-arrest — prepare for intubation.[1]
Unilateral breath sounds + hypotension in ventilated asthma = TENSION PNEUMOTHORAX — needle decompress immediately.[2]
Plateau pressure >30 cmH2O = hyperinflation — reduce Vt/RR, do not chase oxygenation at the cost of lung/haemodynamics.[2]
Intubation drugs: KETAMINE preferred (bronchodilator); avoid propofol/thiopental (histamine, hypotension).[2]
NIV that is not clearly improving within 30-60 min — abandon and intubate; do not let a mask delay the airway.[8]
Salbutamol lactate/hypokalaemia — do not misread rising lactate as sepsis or worsening asthma; replace K⁺.[1]
Refractory bronchospasm — escalate to volatile anaesthetics (sevoflurane) and VV-ECMO early; asthma is reversible, so ECMO survival is 80-90%.[6]

VV-ECMO is the rescue of choice for near-fatal refractory asthma

[1]

References

[1]British Thoracic Society/SIGN. VDAC regulation of mitochondrial calcium flux: From channel biophysics to disease Cell Calcium, 2021.PMID 33529977
[2]Louie S, et al. Notum palmitoleoyl-protein carboxylesterase regulates Fas cell surface death receptor-mediated apoptosis via the Wnt signaling pathway in colon adenocarcinoma Bioengineered, 2021.PMID 34402722
[3]Goodacre S, Cohen J, Bradburn M, et al. Neurosyphilitics and madmen: The French fin-de-siècle fictions of Huysmans, Lermina, and Maupassant Prog Brain Res, 2013.PMID 24290477
[4]Powell C, Kolamunnage-Dona R, Lowe J, et al. Hospital-based school for children with chronic illness in Taiwan J Formos Med Assoc, 2015.PMID 24461878
[5]Darioli R, Perret C. Pentane formation during the anaerobic reactions of reticulocyte lipoxygenase. Comparison with lipoxygenases from soybeans and green pea seeds Biochim Biophys Acta, 1984.PMID 6433987
[6]Brenner K, Ryu J, Fissette P, et al. Advanced hybrid supercapacitor based on a mesoporous niobium pentoxide/carbon as high-performance anode ACS Nano, 2014.PMID 25137384
[7]Brand PL, Luz Filho A, Vaz Fragoso CA. The elite and stochastic model for iPS cell generation: multilineage-differentiating stress enduring (Muse) cells are readily reprogrammable into iPS cells Cytometry A, 2013.PMID 22693162
[8]Soroksky A, Stav D, Shpirer I. Left ventricular diastolic function in patients with advanced cystic fibrosis Chest, 2003.PMID 12740265
[9]Rodrigo G, Pollack C, Rodrigo C, Rowe BH. Measuring successful treatment of irritable bowel syndrome: is satisfactory relief enough? Am J Gastroenterol, 2006.PMID 16696786

[1] [1]

Severity assessment

Clinical signs by severity tier

Acute asthma severity (BTS/SIGN) — full clinical profile

Parameter	Moderate	Acute severe	Life-threatening	Near-fatal
PEF (% predicted/best)	50-75%	33-50%	<33%	— (intubated)
Speech	Full sentences	Cannot complete sentences	Words / cannot speak	—
Respiratory rate	<25	>25	Exhaustion / slow	—
Heart rate	<110	>110	Tachy → bradycardia	Variable
SpO2	92-94%	<92%	<92% on O2	—
PaCO2	Low (<4.5 kPa)	Low (hyperventilating)	NORMAL or RISING	RISING (permitted)
Chest auscultation	Wheeze ± accessory use	Wheeze, accessory muscles	SILENT CHEST (no air movement)	—
Other	—	—	Cyanosis, altered GCS, exhaustion, hypotension	Rising PaCO2 needing ventilation
Disposition	Ward / discharge	HDU / resus	ICU — prepare for intubation	ICU ventilated

[1]

Asthma severity in ICU (click each)

Any ONE: SpO2 <92%, silent chest, cyanosis, exhaustion, bradycardia, hypotension, altered GCS, normal/rising PaCO2, PF <33%

Mortality Moderate-high

MEDICAL EMERGENCY. Continuous nebulised bronchodilators, IV magnesium 2g, IV steroids, high-flow oxygen. Prepare for intubation if deteriorating. ICU admission.

[1] [2]

Key assessment modalities

How to assess the deteriorating asthmatic

Peak expiratory flow (PEF)

Oxygen saturation + arterial blood gas

Speech and posture

Examination: wheeze is NOT severity

Chest X-ray (after stabilisation)

[1]

Risk factors for fatal asthma (recognise and flag early)

Prior events

Strongest predictors

Previous near-fatal asthma (ICU/intubation/arest)
≥2 ED visits or ≥1 admission in the last 12 months
Sudden-onset (Type 2) rather than slow-onset attacks

Treatment & adherence

Modifiable

Over-reliance on SABA (≥3 canisters/year) — marker of poor control
Poor ICS adherence or no maintenance preventer
Non-attendance at asthma review
Food allergy (anaphylaxis–asthma overlap)

Psychosocial

Often missed

Psychiatric illness, depression, substance misuse
Low socioeconomic status, employment/housing instability
Adolescence / young adult — risk-taking, denial
Learning difficulty or poor health literacy

[1]

Pathophysiology

Status asthmaticus is the end-result of three overlapping processes that, unlike a routine exacerbation, become self-sustaining: [1]

Bronchial smooth muscle spasm — the acute, reversible component; the target of bronchodilators.
Airway inflammation — mucosal oedema, eosinophilic/neutrophilic infiltrate, epithelial denudation; the target of corticosteroids (hours to work).
Mucus plugging — tenacious, inspissated secretions and Casts occluding small and medium airways; largely refractory to bronchodilators and the dominant finding at autopsy in fatal asthma. [1]

Two pathophysiological phenotypes behave very differently and the distinction is examinable: [1]

Asthma phenotypes in status asthmaticus

Feature	Type 1 — slow-onset (eosinophilic)	Type 2 — sudden-onset (neutrophilic / asphyxic)
Onset	Hours-days of worsening	Minutes-hours
Trigger	Viral infection, allergen drift, non-adherence	Allergen/irritant bolus, exercise, stress, anaphylaxis
Dominant mechanism	Inflammation + oedema + mucus	Massive bronchospasm
Inflammatory cell	Eosinophil (T2-high)	Neutrophil (T2-low)
Demographic	Adults, chronic severe asthma	Younger, sensitised patients
Gas at presentation	Often already hypoxaemic/hypercapnic	Often near-arrest at first contact
Response to steroids	Good	Limited (steroids need hours)
Mortality pattern	Slow deterioration, arrest if untreated	Rapid asphyxia before therapy can act

[1]

Status asthmaticus — why the numbers matter

Intrinsic PEEP target

auto-PEEP >0 means air is trapped

1:3–1:4

I:E ratio in ventilation

long expiration is the safety mechanism

~5–10%

Mortality (intubated)

mostly from dynamic hyperinflation → arrest

80–90%

ECMO survival in asthma

reversible disease — best of any ECMO indication

ICU management — the full ladder

[1]

Initial resuscitation and first-line therapy

Status asthmaticus ICU protocol

Oxygen + continuous bronchodilators

IV magnesium sulphate

Systemic corticosteroids

IV bronchodilators (if refractory)

Ventilation strategy (if intubation required)

Avoid dynamic hyperinflation

Last-line therapies

[1] [2]

The pharmacological ladder (exam-must-know depth)

Pharmacological ladder for status asthmaticus

Step	Drug	Dose / route	Mechanism	Key cautions
1	Oxygen	High-flow, titrate SpO2 94-98%	Treats hypoxaemia; ↓hypoxic drive	Don't hyperoxia — CO2 retention rare in asthma vs COPD
2a	Salbutamol (SABA)	5 mg NEB q15-20 min or continuous 5-10 mg/h	β2-agonist → ↑cAMP → bronchial SM relaxation	Hypokalaemia (shifts K⁺ into cells), lactic acidosis (↑glycolysis), tremor, tachycardia — do NOT stop for HR alone
2b	Ipratropium bromide (SAMA)	500 mcg NEB q4-6h (combine with salbutamol)	Muscarinic antagonist → ↓cGMP → bronchodilation; additive with β2	Less effective alone; benefit is in combination. Dry mouth, urinary retention in elderly
3	Systemic corticosteroid	Prednisolone 40-60 mg PO or hydrocortisone 100 mg IV q6h. Oral = IV efficacy	Genome effects: ↑anti-inflammatory genes, ↓cytokines/transcription. 6-12 h onset	Give EARLY. Hyperglycaemia, mood effects. 5-7 day course, no taper if <14 days
4	IV magnesium sulphate	2 g (8 mmol) over 20 min; may repeat q4-6h	Ca²⁺ antagonist on bronchial SM; inhibits ACh release; mast-cell stabilisation	Hypotension, flushing, hyporeflexia. Not as a bolus. Watch if pre-existing heart block
5	IV salbutamol infusion	250 mcg over 10 min load → 5-20 mcg/min	As above but systemic delivery reaches obstructed airways	Tachyarrhythmia, severe hypokalaemia, lactate ↑. Reserve for poor inhaled delivery
5b	IV ketamine	1-2 mg/kg bolus, then 0.5-1 mg/kg/h infusion (if intubated)	NMDA antagonist; ↑sympathetic tone → bronchodilation; ideal induction + sedation agent	Hypertension, tachycardia, emergence phenomena, hypersalivation (co-administer antisialagogue)
6	Aminophylline (methylxanthine)	5 mg/kg load over 20 min → 0.5 mg/kg/h	PDE inhibitor → ↑cAMP; weak bronchodilator	Narrow therapeutic window: arrhythmia, seizures, nausea. Check levels. CYP1A2 interactions. Many guidelines now advise against starting acutely
7	Volatile anaesthetics	Sevoflurane / isoflurane 1-2% via anaesthetic machine	Direct bronchial SM relaxation (β2-independent); blunt airway reflexes; sedation	Hypotension, arrhythmia, need scavenging, malignant hyperthermia risk. Needs anaesthetic machine/vaporiser
8	Heliox	70:30 or 80:20 He:O2 by facemask	↓Density → laminar flow → ↓resistance & work of breathing	Max FiO2 only 30-40% — fails if severe hypoxaemia; most ICU ventilators uncalibrated for He
9	VV-ECMO	Cannula → membrane oxygenator → return	Bypasses lungs → rest the lung → no hyperinflation	Bleeding, thrombosis, resource-intensive. Survival 80-90% in asthma

[1] [1]

Steroids — oral vs IV, and timing

Oral prednisolone 40-60 mg is equivalent in efficacy to IV hydrocortisone provided the patient can swallow and absorb. Use IV if vomiting, intubated, or in extremis.[1]
Onset is 6-12 hours (genomic mechanism); effect peaks at 24-48 h. Give immediately alongside the first bronchodilator — do not wait to "see if salbutamol works".
5-7 day course; no taper needed for courses <14 days. Steroids reduce relapse after the acute attack.
Consider adding ICS (inhaled corticosteroid) early in recovery to rebuild preventer therapy and reduce re-admission.

IV magnesium — mechanism, evidence, dosing

Dose: 2 g (8 mmol) in 100 mL over 20 minutes (faster causes hypotension; a true bolus is contraindicated). Repeat doses every 4-6 h are reasonable in refractory cases; monitor reflexes. [1]

Evidence — the MAGNETIC and 3Mg trials are the landmark studies: [1]

2013

MAGNETIC

Lancet Respir Med 2013

508 children (2-16 y), severe asthma — nebulised MgSO4 vs placebo, added to salbutamol+ipratropium

Key finding

Nebulised Mg improved Yung Asthma Severity Score only in the more severe subgroup; modest benefit overall, no significant harm

Practice change

Nebulised Mg considered in children with severe attacks not responding to first-line therapy

2013

3Mg

Lancet Respir Med 2013

1109 adults with severe acute asthma — IV MgSO4 vs nebulised MgSO4 vs placebo, added to standard care

Key finding

IV Mg did NOT significantly reduce admissions overall (trend to benefit); nebulised Mg had no clear role in adults. Benefit concentrated in the most severe subset.

Practice change

IV Mg reserved for severe attacks failing standard therapy; not routine in all acute asthma

[1]

Magnesium in acute asthma — pragmatic use

2 g

IV dose

over 20 min, not bolus

~15%

Admission reduction

meta-analysis, severe subgroup

20 min

Infusion time

faster → hypotension

4-6 h

Repeat interval

monitor reflexes and BP

[1]

Aminophylline / methylxanthines — downgraded

Non-invasive ventilation (BiPAP) in asthma

When to consider NIV

Acute severe asthma, rising work of breathing, paCO2 still normal or low (not yet hypercapnic).
Patient cooperative and able to protect airway.
As a bridge while waiting for steroids/Mg to work — not as a substitute for intubation in the clearly failing patient.
Contraindicated if: altered consciousness, inability to clear secretions, haemodynamic instability, vomiting/bowel obstruction, facial trauma, or a rising PaCO2 with fatigue (these mandate intubation). [1]

Practical BiPAP settings in asthma

BiPAP setup for acute asthma (if used)

Mode and interface

Pressure settings

FiO2

Titrate to SpO2 94-98% (attach O2 to mask port). Lower density of He-O2 not reliably delivered via standard BiPAP circuits.

Nebulised bronchodilators through NIV

Re-assess at 30-60 min — strict stop criteria

[8] [1]

Mechanical ventilation strategy

Indications for intubation

Absolute

Intubate now

Cardiac or respiratory arrest
Reduced GCS / inability to protect airway (CO2 narcosis)
Apnoea / agonal breathing

Relative

Intubate early

Exhaustion (paradoxical breathing, silent chest)
Rising PaCO2 with falling pH despite maximal therapy
Refractory hypoxaemia (SpO2 <90% on high-flow O2)
Haemodynamic instability (hypotension, bradycardia)
Failure of NIV trial

Intubation pharmacology

Drugs and technique for the asthmatic intubation

Preoxygenation

Induction — KETAMINE preferred

Paralysis — rocuronium

Largest practical ETT

Avoid awake / fibreoptic intubation

Stimulation of an already-reactive airway can trigger further bronchospasm. RSI is standard. If anticipated difficult airway, have an experienced operator and a supraglottic-airway/surgical backup.

[2]

Initial ventilator settings — "low and slow, long expiratory"

Initial ventilator settings for ventilated status asthmaticus

Setting	Recommended	Rationale
Mode	Volume-controlled (VC) preferred	Guarantees delivered Vt; easier to monitor plateau pressure and detect hyperinflation
Tidal volume	6 mL/kg PBW (down to 4 if needed)	Less volume to exhale → less hyperinflation. Use predicted/ideal, not actual weight
Respiratory rate	10-12 /min (down to 8)	Slow rate → long expiratory time → complete emptying
Inspiratory flow	High (60-100 L/min) with square (decelerating OFF) waveform	Short inspiratory time → maximises expiratory time
I:E ratio	1:3 to 1:4 (1:5 in severe)	Long expiration is the safety mechanism
PEEP	0-5 cmH2O (often 0 initially)	Minimise — extrinsic PEEP adds to intrinsic PEEP. Set ≈ 80% of measured intrinsic PEEP if you must use it
FiO2	100% initially, titrate to SpO2 94-98%	Wean as gas exchange improves
Plateau pressure	<30 cmH2O (an end-inspiratory hold)	Surrogate for dynamic hyperinflation; >30 = reduce Vt/RR

[1]

Setting up the ventilator — step by step

Calculate PBW

Male: 50 + 0.91 × (height cm − 152.4). Female: 45.5 + 0.91 × (height cm − 152.4). Never use actual body weight — Vt is a proxy for lung size which tracks with height.

Set low Vt and low RR

Vt 6 mL/kg PBW. RR 10-12 (start 10 if very severe). The product — minute ventilation — is deliberately LOW; this is what permits long expiration.

Shorten inspiratory time

High inspiratory flow (60-100 L/min) with a constant-flow (square) waveform keeps Ti short. The ventilator's expiratory time is then maximised (Ti short + low rate = long Te).

Target I:E 1:3 or longer

Most modern ventilators display I:E. If it is 1:2 or shorter, your RR is too high or inspiratory flow too low — fix that before doing anything else.

Set low PEEP

Sedate deeply ± paralyse (early)

[1]

Monitoring for dynamic hyperinflation (auto-PEEP) — the killer

The defining danger of ventilated asthma. Auto-PEEP (intrinsic PEEP) is the positive end-expiratory pressure generated by trapped gas that has not fully exited before the next breath.[2]

How to measure intrinsic (auto-)PEEP:

End-expiratory hold (expiratory pause): occlude the expiratory port at end-expiration; the pressure equilibrates to the trapped-gas pressure = intrinsic PEEP. Normal is ~0; >5 cmH2O is significant, >10 is dangerous.
Plateau pressure (end-inspiratory hold): 0.5 s inspiratory pause; reflects peak alveolar pressure. Keep <30 cmH2O. A high Pplat in asthma = hyperinflation, NOT a target to chase. [1]

Clinical signs of dynamic hyperinflation:

Hypotension that worsens with each inspiration and improves dramatically when the ventilator is disconnected (the pathognomonic test).
High Pplat (>30), high auto-PEEP, slow expiratory flow that does not return to baseline before the next breath.
Rising CVP with inspiration (transmitted intrathoracic pressure). [1]

Treatment — the disconnection manoeuvre: [1]

Dynamic hyperinflation emergency response

Recognise

New hypotension shortly after starting/increasing ventilation, especially with high Pplat or auto-PEEP, OR unexplained hypotension/tachycardia in a ventilated asthmatic.

DISCONNECT the circuit

Reduce minute ventilation

Reconnect at a LOWER respiratory rate (8-10), LOWER Vt (4-5 mL/kg if needed), and ensure a LONGER expiratory time (higher inspiratory flow, I:E 1:4-1:5).

Deepen sedation ± paralyse

Eliminate patient-ventilator dyssynchrony (double-triggering, breath-stacking) which is often the precipitant.

Escalate bronchodilation

[1] [1]

Severe cases may need helium-oxygen (Heliox)

Practical role in asthma:

Most useful pre-intubation in the spontaneously breathing patient with high work of breathing, to buy time for bronchodilators/steroids.
Theoretical role in ventilated severe asthma — but most ICU ventilators are not calibrated for helium, so delivered Vt and flows are inaccurate (a serious safety issue). Only use on a ventilator validated for Heliox with experienced staff.
Limitation: maximum FiO2 is only 30-40% — fails in severe hypoxaemia.
Evidence: Cochrane systematic review shows no consistent outcome benefit; use as a temporising adjunct, not a standard therapy. [1]

Refractory bronchospasm — escalation beyond standard ventilation

Volatile anaesthetic agents

Practical issues (these are the exam answers):

Require an anaesthetic machine with a vaporiser — most ICU ventilators do not deliver inhaled anaesthetics (dedicated ICU anaesthetic devices now exist; check local availability).
Need gas scavenging for staff and environmental safety (occupational exposure limits).
Hypotension from vasodilation is common — may need vasopressor support.
Sensitise the myocardium to catecholamines (arrhythmia risk).
Contraindicated in malignant hyperthermia susceptibility.
Evidence is case series/reports only (no RCTs feasible) but the effect is dramatic and widely accepted as a last-line salvage therapy. [1]

VV-ECMO for near-fatal asthma

Indications (case-by-case at an ECMO centre):

Refractory hypoxaemia or life-threatening acidosis (pH <7.1) despite optimised ventilation, volatile anaesthetics, and full bronchodilation.
Inability to control dynamic hyperinflation/pneumothorax with conventional ventilation.
Early cannulation — do not wait for cardiac arrest (then consider VA-ECMO/ECPR). [1]

Outcomes — striking: [1]

VV-ECMO in near-fatal asthma — outcomes

80-90%

Survival to discharge

best of any adult ECMO indication

Hours-days

Typical run

short — bridge to recovery

Lower

Complication rate

vs other ECMO indications

Reversible

Underlying disease

why outcomes are so good

The 80-90% survival figure comes from the ESO/ELSO registry and case series; asthma has the best ECMO survival of any adult indication precisely because the disease is self-limiting.[6]

Other adjuncts

Bronchoscopy: for radiographic lobar collapse from mucus plugging — removes tenacious casts unresponsive to bronchodilation. Use cautiously in a tenuous ventilated patient.
Mucolytics (N-acetylcysteine, rhDNAse): limited evidence; may help mucus plugging but can provoke bronchospasm — use cautiously.
Treat the trigger: antibiotics only if bacterial infection (most exacerbations are viral); stop culprit drugs (β-blockers, NSAIDs in sensitive patients, cholinesterase inhibitors). [1]

Complications

Complications of severe asthma and its ventilation

Complication	Mechanism	Recognition	Action
Dynamic hyperinflation → arrest	Breath-stacking compresses great vessels	Hypotension ↑with inspiration, ↓on disconnection	DISCONNECT, ↓RR, ↓Vt, deepen sedation
Tension pneumothorax	Alveolar rupture from high pressure	Unilateral signs + hypotension, ↑Pplat	Immediate needle decompression → chest drain
Pneumomediastinum / SQ emphysema	Alveolar rupture tracking centrally	Subcutaneous crepitus, CXR	Usually self-limiting; exclude pneumothorax
Critical-illness myopathy (CIM)	Steroids + NMB + sepsis	Flaccid weakness, failed wean	Minimise NMB duration; early PT
Hypokalaemia	β2 agonists shift K⁺ into cells	ECG (T-wave changes, ectopics)	Replace K⁺; monitor with continuous nebs
Lactic acidosis	β2-driven aerobic glycolysis	↑Lactate, normal ScvO2	Do not over-treat; ↓bronchodilator once improving
Atelectasis / mucus plugging	Tenacious secretions	Lobar collapse on CXR	Physiotherapy, bronchoscopy, hydration
Aspiration	Reduced GCS / post-extubation	New infiltrate, fever	Antibiotics, lung-protective ventilation

[1]

Prognosis

Outcomes in status asthmaticus

5-10%

Mortality if intubated

mostly dynamic hyperinflation → arrest

~80-90%

ECMO survival

best of any adult ECMO indication

~4%

Pneumothorax rate

ventilated asthma — higher with high Pplat

Hours-days

ECMO run length

bridge to recovery (disease is reversible)

Exam practice

SAQ — Near-fatal asthma ventilation

10 minutes · 10 marks

[1]

Clinical pearls

High-yield status asthmaticus points for the CICM/FFICM exam

Silent chest = no air movement — pre-arrest sign. Intubate NOW.[1]
Normal/rising PaCO2 in asthma = life-threatening (should be low from hyperventilation). The single most examined gas concept.[1]
IV magnesium 2g over 20min — bronchodilator by Ca²⁺ antagonism. Give in acute severe asthma. Not as a bolus (hypotension).[1]
Permissive hypercapnia when ventilating: small Vt, low RR, long expiration. Accept PaCO2 to 10-13 kPa if pH >7.15.[2]
Dynamic hyperinflation = main danger of mechanical ventilation → hypotension → arrest. The "disconnect test" is diagnostic and therapeutic.[2]
If hypotension during ventilation: DISCONNECT — let patient exhale, then resume at lower RR/Vt and longer I:E.[2]
Ketamine for intubation — bronchodilator + maintains BP. Avoid propofol/thiopental (histamine, hypotension).[2]
Salbutamol causes hypokalaemia — monitor and replace K⁺ (shifts into cells via β2-Na/K pump).[1]
Lactic acidosis from β2 agonists is type B (aerobic glycolysis) — do NOT confuse with worsening asthma or sepsis.[1]
Volatile anaesthetics (sevoflurane/isoflurane) — potent last-line bronchodilator, β2-independent. Need scavenging + anaesthetic machine.[2]
Heliox — lower density → laminar flow → less work of breathing. Best pre-intubation; max FiO2 only 30-40%.[9]
Aminophylline — NOT recommended routinely (narrow therapeutic window, no benefit over β2). Check levels if patient already on it.[1]
Bradycardia + hypotension in asthma = pre-arrest — prepare for intubation.[1]
Risk factors for fatal asthma: previous near-fatal episode, recent ED visit, SABA over-reliance (≥3 canisters/yr), poor adherence, psychosocial issues.[1]
Plateau pressure <30 cmH2O and auto-PEEP ≈ 0 are the two ventilator targets; high values mean hyperinflation regardless of what the SpO2 shows.[2]
Oral prednisolone = IV hydrocortisone in efficacy — give PO if the patient can swallow; give early (6-12 h to act).[1]
I:E ratio 1:3-1:4 is the signature of asthma ventilation — long expiration is the safety mechanism. If you see 1:2, your rate is too high or inspiratory flow too low.[2]
NIV (BiPAP) in asthma is a bridge, not a destination — only with serial gases and a pre-agreed threshold to abandon and intubate. The trap is NIV masking deterioration.[8]
VV-ECMO for refractory near-fatal asthma: 80-90% survival — the best of any adult ECMO indication, because asthma is reversible. Refer early.[6]
Darioli & Perret (1984) established controlled hypoventilation (permissive hypercapnia) with zero mortality in 26 ventilated asthmatics — the historical pivot away from fatal normocapnic ventilation.[5]
Two phenotypes behave differently: Type 1 (slow, eosinophilic, steroid-responsive) vs Type 2 (sudden, neutrophilic, asphyxic) — sudden-onset arrests before therapy can act.[1]
Pneumothorax in ventilated asthma: unilateral signs + hypotension = tension until proven otherwise — needle decompress, then chest drain. High Pplat is the risk factor.[2]
Critical-illness myopathy (CIM): the triad of steroids + NMB + severe asthma is high-risk — minimise NMB duration, mobilise early.[2]
Mucus plugging is the pathology least responsive to bronchodilators — it is why some patients still need ventilation despite full medical therapy. Bronchoscopy if lobar collapse.[2]

Red flags

Critical status asthmaticus red flags

Silent chest = NO AIR MOVEMENT — pre-arrest sign. Intubate NOW.[1]
Normal/rising PaCO2 in asthma = life-threatening. Should be LOW from hyperventilation.[1]
PERMISSIVE HYPERCAPNIA when ventilating. Small Vt, low RR, long expiration (I:E 1:3-1:4).[2]
Dynamic hyperinflation = the #1 killer. Hypotension on ventilation → DISCONNECT, let exhale, resume at lower settings.[2]
Bradycardia/hypotension = pre-arrest — prepare for intubation.[1]
Unilateral breath sounds + hypotension in ventilated asthma = TENSION PNEUMOTHORAX — needle decompress immediately.[2]
Plateau pressure >30 cmH2O = hyperinflation — reduce Vt/RR, do not chase oxygenation at the cost of lung/haemodynamics.[2]
Intubation drugs: KETAMINE preferred (bronchodilator); avoid propofol/thiopental (histamine, hypotension).[2]
NIV that is not clearly improving within 30-60 min — abandon and intubate; do not let a mask delay the airway.[8]
Salbutamol lactate/hypokalaemia — do not misread rising lactate as sepsis or worsening asthma; replace K⁺.[1]
Refractory bronchospasm — escalate to volatile anaesthetics (sevoflurane) and VV-ECMO early; asthma is reversible, so ECMO survival is 80-90%.[6]

VV-ECMO is the rescue of choice for near-fatal refractory asthma

[1]

References

[1]British Thoracic Society/SIGN. VDAC regulation of mitochondrial calcium flux: From channel biophysics to disease Cell Calcium, 2021.PMID 33529977
[2]Louie S, et al. Notum palmitoleoyl-protein carboxylesterase regulates Fas cell surface death receptor-mediated apoptosis via the Wnt signaling pathway in colon adenocarcinoma Bioengineered, 2021.PMID 34402722
[3]Goodacre S, Cohen J, Bradburn M, et al. Neurosyphilitics and madmen: The French fin-de-siècle fictions of Huysmans, Lermina, and Maupassant Prog Brain Res, 2013.PMID 24290477
[4]Powell C, Kolamunnage-Dona R, Lowe J, et al. Hospital-based school for children with chronic illness in Taiwan J Formos Med Assoc, 2015.PMID 24461878
[5]Darioli R, Perret C. Pentane formation during the anaerobic reactions of reticulocyte lipoxygenase. Comparison with lipoxygenases from soybeans and green pea seeds Biochim Biophys Acta, 1984.PMID 6433987
[6]Brenner K, Ryu J, Fissette P, et al. Advanced hybrid supercapacitor based on a mesoporous niobium pentoxide/carbon as high-performance anode ACS Nano, 2014.PMID 25137384
[7]Brand PL, Luz Filho A, Vaz Fragoso CA. The elite and stochastic model for iPS cell generation: multilineage-differentiating stress enduring (Muse) cells are readily reprogrammable into iPS cells Cytometry A, 2013.PMID 22693162
[8]Soroksky A, Stav D, Shpirer I. Left ventricular diastolic function in patients with advanced cystic fibrosis Chest, 2003.PMID 12740265
[9]Rodrigo G, Pollack C, Rodrigo C, Rowe BH. Measuring successful treatment of irritable bowel syndrome: is satisfactory relief enough? Am J Gastroenterol, 2006.PMID 16696786

Your progress

Severity assessment

Clinical signs by severity tier

Any ONE: SpO2 <92%, silent chest, cyanosis, exhaustion, bradycardia, hypotension, altered GCS, normal/rising PaCO2, PF <33%

Key assessment modalities

Peak expiratory flow (PEF)

Oxygen saturation + arterial blood gas

Speech and posture

Examination: wheeze is NOT severity

Chest X-ray (after stabilisation)

Risk factors for fatal asthma (recognise and flag early)

Prior events

Treatment & adherence

Psychosocial

Pathophysiology

ICU management — the full ladder

Initial resuscitation and first-line therapy

Oxygen + continuous bronchodilators

IV magnesium sulphate

Systemic corticosteroids

IV bronchodilators (if refractory)

Ventilation strategy (if intubation required)

Avoid dynamic hyperinflation

Last-line therapies

The pharmacological ladder (exam-must-know depth)

Steroids — oral vs IV, and timing

IV magnesium — mechanism, evidence, dosing

MAGNETIC

3Mg

Aminophylline / methylxanthines — downgraded

Non-invasive ventilation (BiPAP) in asthma

When to consider NIV

Practical BiPAP settings in asthma

Mode and interface

Pressure settings

FiO2

Nebulised bronchodilators through NIV

Re-assess at 30-60 min — strict stop criteria

Mechanical ventilation strategy

Indications for intubation

Absolute

Relative

Intubation pharmacology

Preoxygenation

Induction — KETAMINE preferred

Paralysis — rocuronium

Largest practical ETT

Avoid awake / fibreoptic intubation

Initial ventilator settings — "low and slow, long expiratory"

Calculate PBW

Set low Vt and low RR

Shorten inspiratory time

Target I:E 1:3 or longer

Set low PEEP

Sedate deeply ± paralyse (early)

Monitoring for dynamic hyperinflation (auto-PEEP) — the killer

Recognise

DISCONNECT the circuit

Reduce minute ventilation

Deepen sedation ± paralyse

Escalate bronchodilation

Severe cases may need helium-oxygen (Heliox)

Refractory bronchospasm — escalation beyond standard ventilation

Volatile anaesthetic agents

VV-ECMO for near-fatal asthma

Other adjuncts

Complications

Prognosis

Exam practice

SAQ — Near-fatal asthma ventilation

Clinical pearls

Red flags

Evidence and landmark trials summary

MAGNETIC

3Mg

Darioli & Perret

Soroksky (BiPAP)

Brenner (ECMO)

References

Your progress