Hypoxia
Severity
SpO₂
- MildSpO₂ 92–94%
- SignificantSpO₂ 88–91%
- EmergencySpO₂ < 88% or cyanosis
🚨 Life-Threatening — exclude first
If suspected, escalate now.
Tension pneumothorax
Massive PE
Acute pulmonary oedema
Severe pneumonia / ARDS
Anaphylaxis
Type 2 respiratory failure with acidosis
🔀
V/Q mismatch Causes
Pulmonary embolism
💧
Shunt Causes
Pneumonia / consolidationAcute pulmonary oedemaARDSAtelectasis (post-op, mucous plug)
🫁
Obstructive Causes
Asthma exacerbationCOPD exacerbationForeign body / mucous plug
😴
Hypoventilation Causes
Opioid / sedative oversedationNeuromuscular weaknessExhaustion in severe asthmaPost-op residual anaesthesia
💨
Pleural Causes
Pneumothorax (incl. tension)Large pleural effusion
🩸
Delivery / Other Causes
Anaemia (low O₂ carriage)Methaemoglobinaemia (sats look normal but cyanotic)Cardiac shunt