Oxygen desaturation in patients with functional seizures: pitfalls for the unwary

Functional seizures are one of the most common presentations of functional neurological disorder and frequently generate diagnostic uncertainty in emergency settings. We are experiencing increasing reports of oxygen desaturation during functional seizures, particularly with widespread use of consumer oximeters and wearable devices. We describe a case of recurrent functional seizures with documented desaturation that prompted cardiopulmonary investigations and repeat video-electroencephalogram evaluation. In a controlled setting, apparent desaturations were attributable to artefact and brief breath-holding, with saturations remaining within the expected physiological range. We review common artefactual causes of low oxyhaemoglobin saturation in functional seizures, including motion, excessive pressure due to clenched fingers, excessive ambient light, poor probe placement and low perfusion, as well as the potential role of posthyperventilation apnoea. Recognising these pitfalls is essential to avoid misinterpretation, unnecessary investigations and anxiety for patients and clinicians. Understanding oximetry waveform quality and artefact sources is key to distinguishing true hypoxia from misleading readings.