Several methods of supporting respiratory function of a patient before, during and/or after a medical procedure are disclosed. In certain arrangements, supporting respiratory function while a patient is under general anaesthesia can include providing a high gas flow that is greater than 15 L/min while the patient is under general anaesthesia. In certain arrangements, a method of providing ventilation while a patient is under general anaesthesia involves providing only a gas flow delivered through a nasal interface that is greater than 15 L/min while the patient is under general anaesthesia.