Synopsis
Interpret low oxygen measurements, cyanosis and finger clubbing as distinct clinical signals, confirm artefact or dyshemoglobinaemia, identify the underlying gas-exchange mechanism, and avoid treating signs without investigating their cause.
- Hypoxaemia means low arterial oxygen; hypoxia means inadequate tissue oxygen availability. Anaemia or circulatory failure can produce tissue hypoxia despite a normal PaO2.
- Pulse oximetry estimates saturation, not ventilation or oxygen content. It cannot detect hypercapnia and is affected by poor perfusion, motion, nail products, dyshemoglobinaemia and device bias.
- Central cyanosis involves tongue and oral mucosa and suggests arterial desaturation or dyshemoglobinaemia; peripheral cyanosis can arise from slow flow and vasoconstriction with normal arterial oxygenation.
Key red flags
Low saturation with tachypnoea, work of breathing, confusion, new oxygen need or haemodynamic instability signals acute respiratory failure. Pneumonia, oedema, embolism, pneumothorax and severe airway disease are prioritised by history and examination.
Investigation priorities
Screen and trend arterial saturation while assessing signal reliability.
Management branches
Low saturation with acute symptoms, physiological compromise or increasing oxygen requirement.
- Use ABCDE, verify the oximeter signal, prescribe oxygen to the appropriate target and call senior help when distress, altered consciousness or haemodynamic compromise is present.
- Obtain an arterial blood gas when severe hypoxaemia, hypercapnia risk or ventilatory failure is possible; support ventilation rather than escalating oxygen alone when carbon dioxide and pH show failure.
Key medicines
Controlled oxygenTitrate to SpO2 94-98% for most acutely ill adults or 88-92% pending blood gases when hypercapnic respiratory failure risk is present, unless an individual target is documented.
Cause-specific antidotal treatment for dyshemoglobinaemiaGive high-concentration oxygen immediately for suspected carbon monoxide exposure and use specialist toxicology guidance for hyperbaric assessment or methaemoglobinaemia treatment.