Synopsis
Interpret respiratory failure from the blood gas, identify the failing physiological process and match oxygen, ventilatory support and cause-specific treatment to the patient rather than to a label alone.
- Type 1 respiratory failure is hypoxaemia (commonly PaO2 below 8 kPa) with normal or low PaCO2, caused mainly by V/Q mismatch, shunt or diffusion failure.
- Type 2 respiratory failure is hypercapnia (PaCO2 above the laboratory upper reference, often over 6.0 kPa) from inadequate alveolar ventilation, often with hypoxaemia.
- Acute hypercapnic respiratory failure requiring NIV assessment is conventionally pH below 7.35 with PaCO2 above 6.5 kPa after initial treatment.
Key red flags
Low PaO2 with normal/low PaCO2: consider pneumonia, pulmonary oedema, PE, pneumothorax, acute asthma, ARDS or interstitial lung disease.
Investigation priorities
Classify oxygenation, ventilation and acid–base status.
Management branches
Any suspected acute respiratory failure.
- Perform ABCDE, sit upright if appropriate, call for senior help when severe and prescribe a target saturation.
- Give controlled oxygen: usually 94–98%, or 88–92% if hypercapnia risk. Obtain an ABG promptly and record device/flow.
Key medicines
Naloxone for suspected opioid overdose400–2000 micrograms IV initially in coma or significant respiratory depression, repeated every 2–3 minutes if needed up to 10 mg; in opioid-dependent or postoperative patients, titrate smaller 100–200 microgram IV increments to adequate ventilation.
Nebulised salbutamol2.5–5 mg nebulised, repeated according to severity and response; in hypercapnia risk, drive the nebuliser with compressed air and maintain target oxygen separately where possible.