Inhalational anaesthesia is a common technique for the maintenance of anaesthesia, where low fresh gas flow rates are fed into a circle system. Oxygen/air or oxygen/nitrous oxide mixtures are normally combined with an inhalational agent.

At the end of a procedure, the inhalational agent should be turned off and higher flows (>6 L/min) of oxygen on its own should be administered.

As with preoxygenation performed at induction, this provides a reservoir of oxygen in the lungs. This enables oxygenation to be maintained during periods of hypoventilation or obstruction. It also facilitates washout of nitrogen/nitrous oxide and vapours from the patient’s body and the anaesthetic circuit.

It takes three to five minutes to wash out most of the nitrous oxide which should be completed prior to extubation to ensure the patient has a reservoir of oxygen in the lungs.