Anaes · Volatile & inhalational agents

Xenon

Also known as Xe (element 54) · Noble gas anaesthetic · Inert gas anaesthetic · Lowest blood-gas coefficient agent · NMDA-antagonist inhalational agent

Xenon (Xe, element 54) is an inert noble-gas inhalational anaesthetic whose blood-gas partition coefficient of 0.115 is the LOWEST of any agent, giving extremely rapid onset and offset and clear emergence (Baima 2026; Chen 2026). Its MAC is around 71 percent (about 63 percent in the elderly), so it is a weaker anaesthetic than the halogenated volatiles and is given at high inspired concentrations. It is completely inert, not metabolised, with no toxic metabolites; it does not trigger malignant hyperthermia; and it is neither a greenhouse gas nor ozone-depleting. It is haemodynamically very stable, with minimal myocardial depression and no catecholamine sensitisation, making it useful in cardiac disease and the elderly (Hendrix 2026). As an NMDA receptor antagonist it provides analgesia (Ma 2025), and through NMDA antagonism, two-pore-domain potassium-channel (TREK) activation and preconditioning it is neuroprotective and cardioprotective — studied in neonatal hypoxic-ischaemic encephalopathy with cooling, cardiac arrest, traumatic brain injury and myocardial preservation (Chen 2026; Ponomarev 2025; Zamora 2026; Sienel 2026). The main limitations are COST and SCARCITY: xenon is a trace atmospheric gas extracted by fractional distillation of liquid air, expensive, and needs a specialised low-flow closed-circuit delivery system.