General anaesthesia

General anaesthesia (UK) or general anesthesia (US) is medically induced loss of consciousness that renders a patient unarousable even by painful stimuli. It is achieved through medications, which can be injected or inhaled, often with an analgesic and neuromuscular blocking agent. General anaesthesia is usually performed in an operating theatre to allow surgical procedures that would otherwise be intolerably painful for a patient, or in an intensive care unit or emergency department to facilitate endotracheal intubation and mechanical ventilation in critically ill patients. Depending on the procedure, general anaesthesia may be optional or required. No matter whether the patient prefers to be unconscious or not, certain pain stimuli can lead to involuntary responses from the patient, such as movement or muscle contractions, that make the operation extremely difficult. Thus, for many procedures, general anaesthesia is necessary from a practical point of view. The patient's natural breathing may be inadequate during the procedure and intervention is often necessary to protect the airway. Various drugs are used to achieve unconsciousness, amnesia, analgesia, loss of reflexes of the autonomic nervous system, and in some cases paralysis of skeletal muscles. The best combination of anaesthetics for a given patient and procedure is chosen by an anaesthetist or other specialist in consultation with the patient and the surgeon or practitioner performing the procedure.