What is an anaesthetic?

Someone in your family may have had an operation. Have you wondered why they are made to sleep before being taken to the operation theatre?

What is an anaesthetic?

An anaesthetic is a substance that causes the three As – analgesia (no pain), amnesia (no memory) and anaesthesia (no consciousness). All medically used anaesthetics are also reversible in their actions; the patient is back to normal once the concentration of anaesthetic in the body reduces. Those that act on the whole body are called general anaesthetics while those limited to a particular body part are called local anaesthetics.

An anaesthetic causes the three As – analgesia (no pain), amnesia (no memory) and anaesthesia (no consciousness).

Commonly used anaesthetics

The most common anaesthetic is ethyl alcohol. Whenever you get an injection, the ethyl alcohol acts as a local anaesthetic, temporarily paralyzing the nerve endings on your skin. Dentists use a mixture of nitrous oxide and Novocain as an anaesthetic when working on your teeth.

Chloroform was the first widely used general anaesthetic. It was made famous in 1853 when Queen Victoria allowed it to be used on her during childbirth. However it is toxic even in small concentrations, and has since been replaced by ether and other gaseous anaesthetics like xenon, desflurane, isoflurane and sevoflurane.

How do anaesthetics work?

Anaesthesia is still an empirical science –what this means is that though the phenomenon is known and can be put to use, how it works in the body is still unknown. Nevertheless, a few facts are known. It is understood that they act on the membrane that covers all the cells in our nervous system. At the level of the cell, there are two main theories neuroscientists think possible.

Lipid hypothesis

The membrane of a cell is made of a layer of lipids (fats), in which many proteins are embedded. These proteins transport materials in and out of cells, and their activity depends on their shape. According to the lipid hypothesis, when an anaesthetic substance is introduced to the body, it lodges in the lipid membrane. This indirectly cause changes in the shape of the proteins in it, leading to shut down of cell functions.

Protein hypothesis

This hypothesis holds that anaesthetics interact directly with proteins, causing shape changes, and hence changes in function.

Research into the mechanisms of anaesthesia is still an active field, and preliminary evidence for both theories has been shown. Maybe you will take up a career in anaesthesia research and give us the final answer!

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