Drugs that act on the brain to induce unconsciousness for surgery
General anaesthetics produce reversible loss of consciousness and sensation and are therefore used in people undergoing surgery (see Having a general anaesthetic). The drugs are rapidly absorbed by the brain and produce unconsciousness by reducing the flow of nerve impulses in the brain.
How are they used?
Initially, a short-acting drug such as etomidate or propofol is injected to induce anaesthesia. The effect of these drugs wears off quite quickly so to maintain anaesthesia, inhaled anaesthetics are administered, either via a face mask or an endotracheal tube (a flexible tube passed into the windpipe through the nose or mouth). Often, a muscle relaxant drug is given in addition to the general anaesthetics. This relaxes all the muscles in the body, including those of the throat and respiratory system. Consequently, breathing has to be assisted artificially and vital body functions, such as heart rate and blood pressure, are monitored continuously during a general anaesthetic.
Various general anaesthetics are often combined so that only a minimum dose of each drug is needed to maintain unconsciousness. This method reduces the potential for side effects from any of the drugs. For minor surgical procedures, an injected general anaesthetic is sometimes used without inhaled anaesthetics.
When the surgical procedure is completed, the anaesthetics are stopped and, if necessary, drugs are administered to reverse muscle relaxation.
What are the side effects?
Modern general anaesthetics have few side effects and recovery is usually prompt. The most common side effects on regaining consciousness are nausea and vomiting, which can be controlled with antiemetic drugs if necessary, and tiredness. Rarely, some inhaled anaesthetics may cause liver damage if given repeatedly. Your doctor or anaesthetist will ask if you have had a general anaesthetic within the last 3 months and whether you have had any adverse reactions to an anaesthetic.
Certain other drugs, such as those used to treat high blood pressure, may interact with anaesthetics. You should inform your anaesthetist about any drugs you have been taking, whether prescription, over-the-counter, recreational, or complementary remedies.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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