How do anaesthetics work

An anaesthetist administers chemicals such as halothane (HI) to a patient before and during an operation to promote unconsciousness. Medical procedures such as operations would be impossible for the surgeon if the patient were awake and could move and they would also be traumatic for a patient who was aware of what the surgery entailed. 

A really deep, chemically induced sleep is termed narcosis, from the Greek narke, meaning numbness. Similarly, we similarly call a class-A drug a narcotic.  

Henry s law is named after William Elenry (1775-1836), and says that the amount of gas dissolved in a liquid or solid is in direct proportion to the partial pressure of the gas. 

Although the topic of anaesthesia is hugely complicated, it is clear that the physiological effect of the compounds depends on their entrapment in the blood. Once dissolved, the compounds pass to the brain where they promote their narcotic effects. It is now clear that the best anaesthetics dissolve in the lipids from which cell membranes are generally made. The anaesthetic probably alters the properties of the cell membranes, altering the rates at which neurotransmitters enter and leave the cell. 

A really deep sleep requires a large amount of anaesthetic and a shallower sleep requires less material. A trained anaesthetist knows just how much anaesthetic to administer to induce the correct depth of sleep, and achieves this by varying the relative pressures of the gases breathed by the patient. 

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