Anaesthesia is the deliberate, controlled and reversible loss of sensation induced to allow a medical procedure to be carried out safely and without pain. It is delivered by anaesthetists working with anaesthetic associates and operating department practitioners, and it extends well beyond the procedure itself into preoperative assessment, intraoperative physiological management and recovery.
Modern general anaesthesia is often described as a triad of hypnosis (unconsciousness), analgesia (pain relief) and, where required, muscle relaxation. Each element is titrated to the patient and the operation, using intravenous agents such as propofol, inhalational agents, opioids and neuromuscular blocking drugs as appropriate.
Risk is assessed before the procedure using history, examination, functional capacity and investigations. The American Society of Anesthesiologists physical status classification (ASA grade) provides a shared shorthand for a patient's overall fitness. Assessment also covers airway prediction, previous anaesthetic problems, allergies, medication including anticoagulants, and family history of conditions such as malignant hyperthermia.
Continuous monitoring is mandatory throughout: pulse oximetry, capnography, electrocardiography, blood pressure and temperature as a minimum, with depth of anaesthesia and neuromuscular monitoring used where indicated. Anaesthesia has become dramatically safer over recent decades, largely through standardised monitoring, safety checklists, capnography for airway confirmation and systematic learning from national audit.
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