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

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.

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 doesn't get processed or recognised by the brain.

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 medication

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)
  • gas that you breathe in through a mask

The anaesthetic should take effect very quickly. You'll start feeling light-headed, 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.


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 24-48 hours.

Side effects

General anaesthetics have some common side effects. Your anaesthetist should discuss these with you before your surgery.

Most side effects occur immediately after your operation and don't last long. Possible side effects include:

  • feeling sick and vomiting – this usually occurs immediately, although some people may continue to feel sick for up to a day
  • shivering and feeling cold – this may last a few minutes or hours
  • confusion and memory loss – this is more common in elderly people or those with existing memory problems; it's usually temporary, but occasionally can be longer lasting
  • bladder problems you may have difficulty passing urine
  • dizziness – you will be given fluids to treat this
  • bruising and soreness – this may develop in the area where you were injected or had a drip fitted; it usually heals without treatment
  • sore throat – during your operation, a tube may be inserted either into your mouth or down your throat to help you breathe; afterwards, this can cause a sore throat
  • damage to the mouth or teeth – a small proportion of people may have small cuts to their lips or tongue from the tube, and some may have damage to their teeth; you should tell your anaesthetist about any dental work you have had done

Complications and risks

A number of more serious complications are associated with general anaesthetics. These are rare, occurring in less than 1 in every 10,000 cases.

Possible serious complications and risks include:

  • a serious allergic reaction to the anaesthetic (anaphylaxis)
  • an inherited reaction to the anaesthetic that causes breathing difficulties
  • waking up during your operation – but this is rare, and the amount of anaesthetic given will be continuously monitored to help ensure this doesn't happen
  • death – this is very rare, occurring in 1 in every 100,000 to 1 in every 200,000 cases

Serious problems are more likely to occur if you're having major or emergency surgery, you have any other illnesses, you smoke, or you're overweight.

Your anaesthetist will discuss the risks with you before your operation. You should try to stop smoking or drinking alcohol in the weeks before surgery, as doing so will reduce your risk of developing complications.

You may also be advised to lose weight, and if you can you should increase your activity levels in the weeks before surgery, as this is likely to reduce your risk as well.

In most cases, the benefits of being pain-free during an operation outweigh the risks.

Other types of anaesthetic

As well as general anaesthetic, there are several other types of anaesthetic, which can be used for certain procedures. They include:

Page last reviewed: 08/05/2015

Next review due: 08/05/2017