general anaesthetic

A general anaesthetic is a drug that produces controlled, reversible unconsciousness so that surgery can be carried out painlessly. Unlike a local anaesthetic, which numbs one spot, a general anaesthetic acts on the whole brain, switching off awareness, memory, and the ability to respond — and then, crucially, letting the patient wake up unharmed when the drug is stopped.

These drugs are given two ways: as gases or vapours breathed in (such as sevoflurane and nitrous oxide) and as liquids injected into a vein (such as propofol). Most work by enhancing inhibitory signaling in the brain, especially by boosting the effect of the calming neurotransmitter GABA at its receptor, so that neurons fire less and consciousness fades. Ketamine is an exception, working mainly by blocking the excitatory NMDA receptor instead.

True general anaesthesia is rarely one drug but a balanced combination — a hypnotic to abolish awareness, an analgesic (often an opioid) to block pain, and sometimes a neuromuscular blocker to keep muscles still. The anaesthetist's real skill is steering a narrow course: deep enough that the patient feels nothing, light enough that breathing and blood pressure are maintained, because the same drugs that abolish consciousness also depress the heart and lungs. This is one of medicine's clearest examples of a drug used right at the edge of its therapeutic window.