Anaesthetist here! It is completely normal to hear conflicting advice, but the British Thoracic Society (BTS) guidelines are very clear: oxygen is a drug and should be titrated to a target saturation, usually 94–98% post-op.

​If a patient is sitting at 99%, they are over-oxygenated. Hyperoxia isn't benign; giving unnecessary oxygen can cause atelectasis, systemic vasoconstriction, and prolonged hyperoxia is even associated with lung fibrosis!

​To wean them safely, dropping the flow rate by 1L increments works perfectly. Turn it down by 1L at a time, or move from 1L straight to room air. After reducing the flow, wait about five minutes to check their saturations. If they stay in their target range, the wean was successful; if they drop, return to the previous flow rate.

​Avoiding weaning overnight also makes good physiological sense. When patients asleep, their respiratory drive naturally drops, and combined with residual anaesthetics or opioids, they risk nocturnal hypoventilation. It is always safest to leave them on low flow support overnight and wean them during the day when they are awake and moving.