Anaesthesia
Drugs that remove sensation; general anaesthesia makes a patient unconscious and free of pain during surgery.
The word anaesthesia comes from Greek for "without sensation". A local anaesthetic numbs one part of the body, as at the dentist. A general anaesthetic goes much further, putting the patient into a controlled, reversible unconsciousness in which they feel no pain, do not move and remember nothing of the operation.
Before anaesthesia, surgery was a race against agony, and speed was a surgeon's most prized skill. In Japan, Hanaoka Seishū operated under a herbal general anaesthetic in 1804. In the West the turning point came at Massachusetts General Hospital in Boston on 16 October 1846, when the dentist William Morton gave ether to a patient during an operation and the patient felt no pain. In 1845 the dentist Horace Wells had tried to demonstrate nitrous oxide, "laughing gas", and the patient cried out. Chloroform soon followed. Freed from the need for haste, surgeons could develop longer and more delicate operations.
Gases such as ether and nitrous oxide work by dissolving in the blood and travelling to the brain. How quickly they act and wear off depends on their concentration and on how readily they dissolve in blood. Too little, or too short an exposure, and the patient may still react, one reason early demonstrations could fail.
The gap between a dose that keeps someone safely unconscious and one that is dangerous can be narrow, which is why anaesthetists monitor every patient continuously.
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