Temporal Dynamics of Peripheral SpO₂ During Reoxygenation

Pulse oximeters estimate arterial oxyhaemoglobin saturation (SaO₂) from photoplethysmographic signals recorded at peripheral sites (usually the fingertip), thus measuring the peripheral oxygen saturation (SpO₂). They are ubiquitous in emergency medicine because they offer a non-invasive, continuous measure of oxygenation and can alert clinicians to impending hypoxaemia, both during procedures such as rapid sequence intubation or sedation, or for continuous monitoring of patients. However, the accuracy of SpO₂ is often assumed to be instantaneous. This assumption is particularly hazardous during critical events involving rapid desaturation and resaturation. In such situations clinicians use SpO₂ readings to decide when to stop an apnea period during laryngoscopy and commence reoxygenation. If there is a delay between actual arterial desaturation and the displayed SpO₂, the clinician may not recognise hypoxaemia in time or may resume ventilation too late.