Acute respiratory failure: classification and approach

Also known as Type 1 respiratory failure (hypoxaemic) · Type 2 respiratory failure (hypercapnic) · A-a gradient · Respiratory failure approach

Acute respiratory failure is the inability of the respiratory system to maintain adequate gas exchange. Type 1 (hypoxaemic): PaO2 <60 mmHg (8 kPa) on room air, normal/low PaCO2. Causes: V/Q mismatch (1 — pneumonia, PE, pulmonary oedema, ARDS), shunt, diffusion impairment, hypoventilation. Type 2 (hypercapnic): PaCO2 45 mmHg (6 kPa). Causes: alveolar hypoventilation (COPD, neuromuscular disease, CNS depression), increased CO2 production (sepsis, burns), V/Q mismatch with fatigue. Approach: ABCDE, identify type (blood gas), treat underlying cause, oxygen therapy, ventilatory support (NIV or intubation). Key formula: A-a gradient (Alveolar-arterial oxygen gradient) distinguishes hypoxaemia causes.

high20 referencesUpdated 26 July 202613 min readVerification in progress

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8 MCQs

Meet the patient

A 64-year-old man with COPD arrives at 02:00 with three days of worsening dyspnoea, productive sputum, and confusion. RR 34, SpO2 84 per cent on air, pursed-lip breathing, accessory muscles recruited, GCS 13. ABG on a Hudson mask: pH 7.26, PaCO2 72, PaO2 52, HCO3 30. Twenty minutes ago his ABG showed PaCO2 58 — the CO2 is climbing, the pH is falling, the muscle pump is failing.^[16]

Two facts decide the next hour. This is Type 2 hypercapnic failure from ventilatory pump fatigue, not a primary lung problem — and the normal A-a gradient proves it. And his clinical sign — the agitation that flipped to confusion in the last ten minutes — is the muscle pump decompensating, not anxiety. Hold those two facts and the rest of this topic slots into place.^[16]

References20Show

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