It's not clear exactly how it works, but it's known that all anaesthetics interrupt the passage of signals along the nerves.  This means that any stimulation to the body does not get processed or recognised by the brain. 

General anaesthesia is essential for some surgical procedures where it may be safer or more comfortable for you to be unconscious.  It's usually used for long operations or those that would otherwise be very painful. 

General anaesthesia is a state of controlled unconsciousness.  During a general anaesthetic, medicines are used to send you to sleep, so you're unaware of surgery and do not move or feel pain while it's carried out. 

How general anaesthetics are given

Before having an operation, you'll meet a specialist doctor called an anaesthetist to discuss which anaesthetic is most suitable for you. 

Your anaesthetist will look at your medical history and will ask whether anyone in your family has had problems with anaesthesia.  They'll also ask about your general health and lifestyle, including whether you:

have any allergies

smoke or drink alcohol

are taking any other medicine

Your anaesthetist can answer any questions you have.  Let them know if you're unsure about any part of the procedure or if you have any concerns.  You should be given clear instructions to follow before the operation, including whether you can eat or drink anything in the hours leading up to it. 

Before and during your operation

Just before you have surgery, you'll usually be taken to a room where your anaesthetist will give you the general anaesthetic. 

It will either be given as a:

liquid that's injected into your veins through a cannula (a thin, plastic tube that feeds into a vein, usually on the back of your hand)

that's injected into your veins through a cannula (a thin, plastic tube that feeds into a vein, usually on the back of your hand) gas that you breathe in through a mask

The anaesthetic should take effect very quickly.  You'll start feeling lightheaded, before becoming unconscious within a minute or so. 

Your anaesthetist will stay with you throughout the procedure.  They'll make sure you continue to receive the anaesthetic and that you stay in a controlled state of unconsciousness.  They'll also give you painkilling medicine into your veins, so that you're comfortable when you wake up. 

Recovery

After your operation, the anaesthetist will stop the anaesthetic and you'll gradually wake up.  You'll usually be in a recovery room at first, before being transferred to a ward. 

Depending on your circumstances, you'll usually need to stay in hospital for a few hours to a few days after your operation. 

General anaesthetics can affect your memory, concentration and reflexes for a day or two, so it's important for a responsible adult to stay with you for at least 24 hours after your operation, if you're allowed to go home.  You'll also be advised to avoid driving, drinking alcohol and signing any legal documents for 24 to 48 hours.