Respiratory Failure and Non-Invasive Ventilation — Written Clinical Reasoning

Model answer — Part A: the acidotic COPD exacerbation

Frame the problem first. This is acute-on-chronic type 2 respiratory failure with a respiratory acidosis (pH below 7.35) persisting despite one hour of maximal medical therapy on controlled oxygen — the textbook trigger for NIV. The HCO3 of 31 signals a degree of chronic retention underneath the acute decompensation [1].

Immediate assessment runs alongside treatment: severity (work of breathing, conscious level, haemodynamics), the driver (infective exacerbation — sputum, cultures, CXR to exclude pneumonia or pneumothorax), the contraindication screen for NIV (he is cooperative, not vomiting, haemodynamically stable — none present), and the escalation question — is he for intubation if NIV fails? I document that ceiling decision before starting [1].

Management: continue controlled oxygen to target SpO2 88–92%, and commence bilevel NIV now — IPAP starting at 10 cmH2O titrated up toward 20–30 as tolerated, EPAP 4–5, in a monitored setting. The evidence anchor is the Plant ward RCT (intubation halved, in-hospital mortality reduced) consolidated by the Cochrane meta-analysis showing reduced mortality and intubation in acidotic COPD exacerbations [2] [3].

Judging success is protocolised: repeat the ABG at 1–2 hours. Success is a rising pH, falling PaCO2, falling respiratory rate and improving comfort. Failure is a static or falling pH, rising PaCO2, exhaustion, copious secretions or deteriorating conscious level — and failure in a patient for escalation means intubation without further delay, a threshold I write down at the start [1] [2].

Model answer — Part B: hypoxaemic pneumonia — HFNO, NIV or intubation?

Define the failure. This is type 1 (hypoxaemic) failure with normocapnia from viral pneumonia — the physiology is V/Q mismatch and shunt, not pump failure, so the support must match oxygenation failure, not ventilatory failure [5].

The choice: high-flow nasal oxygen first-line. FLORALI showed that in acute hypoxaemic respiratory failure (predominantly pneumonia), HFNO reduced 90-day mortality compared with conventional oxygen and with NIV, with fewer intubations in the more hypoxaemic subgroup; comfort and reliable FiO2 delivery are the practical advantages [5]. NIV is deliberately not first-line here: the landmark pneumonia RCT (Confalonieri) found benefit only in the subgroup WITH underlying COPD, and the ERS/ATS guideline urges caution in de novo hypoxaemic failure because NIV failure delays intubation and is associated with harm [7] [8]. Immediate intubation is not yet mandated — she is alert and normotensive — but the threshold is explicitly low.

Monitoring the trial: continuous oximetry and respiratory rate, FiO2 requirement trajectory (a ROX-style assessment), work of breathing and gas exchange on repeat ABG. Predefined failure criteria — rising oxygen requirement, worsening tachypnoea or exhaustion, any shock or deteriorating conscious level — trigger intubation, because delayed intubation after failed non-invasive support is the outcome the evidence warns against [6] [8]. I close by stating that the definitive levers remain antiviral/antibacterial therapy, supportive care, and early recognition of deterioration — the device only buys time for them.