Health: Common procedures: Anaesthetics

DIARIES written earlier than 1850 often include grim accounts of the appalling pain endured by people undergoing surgery. Fanny Burney described the knife grating against the bone as Baron Larrey (Napoleon's surgeon) removed her breast cancer. Surgeons had assistants to hold their patients down, doped them with alcohol, and tried techniques such as mesmerism - but they relied mostly on speed: an amputation of the leg was done in less than 30 seconds.

Haste and terror came to an end with the demonstration in the mid-19th century that ether, chloroform and nitrous oxide (laughing gas) could put people into a temporary state of unconsciousness from which surgery would not wake them. The ideal anaesthetic puts the patient to sleep, abolishes pain, and relaxes the muscles, which is essential if the surgeon needs to get his hands and his instruments inside one of the body cavities.

The early anaesthetics achieved all three aims by putting the patient into a deep coma, so close to death that the heart or breathing might stop. Dying under the anaesthetic was a small risk, accepted in times when surgery was done only for life-threatening illness. Gradually, however, safer drugs were introduced, and surgeons and the public came to expect routine operations to be virtually free of hazard. Modern anaesthesia is extremely safe, but it is also extremely complicated.

Nowadays a specialist anaesthetist starts by giving a tranquillising sedative and another drug to dry the mouth and the lungs. This combination is called the premedication, and is usually given about an hour before the operation, making the patient drowsy and relaxed. On arrival at the operating theatre the anaesthetist induces loss of consciousness with one drug (such as an injection of thiopentone), maintains unconsciousness with another (often a combination of nitrous oxide and halothane), and uses a third drug to cause muscular paralysis (usually one of a group of drugs based on South American arrow poison). Because the muscles are paralysed, the patient's breathing is controlled by a machine connected to the lungs by a tube going into the windpipe.

During the operation, the anaesthetist monitors the effects of all these drugs on the patient's blood pressure and pulse rate, how much oxygen is getting into the lungs, and the level of consciousness - making sure the patient does not drift back into awareness while still paralysed. After surgery, further drugs are given to reverse the muscle relaxation and relieve pain.

All this sounds, and is, very complicated when compared to simply putting a gauze funnel soaked in ether over the patient's nose. The advantages of the complicated methods are that they are safer (and most of the drugs in current use have been around for 20 years or more, and so are well-tested), and that when patients recover they do not feel as sick and miserable as was the case with the early anaesthetics. The risks of anaesthesia are now so low that operations on 80-year-olds are routine. Nevertheless, all operations do still carry a small but unavoidable risk; the heart may still stop, blood clots may form and be carried to the lungs. Samuel Pepys always celebrated the anniversary of his survival of his surgery for a bladder stone, and we can still understand his response.