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Anaesthetic, general

Page last reviewed: 13/07/2011

General anaesthetic is a type of anaesthesia (a medication that causes loss of sensation). It is used for pain relief during surgical procedures. A general anaesthetic makes you completely lose consciousness so that surgery can be performed without causing pain or distress.

How does general anaesthetic work?

Anaesthetics work by blocking the signals that pass along your nerves to your brain. Your nerves are bundles of fibres that use chemical and electrical signals to pass information around your body. A general anaesthetic stops your brain recognising the signals coming from your nerves, so that you cannot feel anything.

If you are having a general anaesthetic, it will be given to you by an anaesthetist (a specialist doctor who is trained in anaesthesia). The anaesthetic medication can be given to you in one of the following two ways:

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

Your anaesthetist will stay with you throughout the procedure. They will make sure that you continue to receive the anaesthetic and that you stay asleep, in a controlled state of unconsciousness.

After the operation is over, your anaesthetist will reverse the anaesthetic and you will gradually begin to wake up.

When is general anaesthetic used?

General anaesthetic is essential for some surgical procedures where it may be safer or more comfortable for you to be unconscious.

It is usually used for long operations, or those which could be very painful. For example:

  • transplant operations - where a diseased organ is removed and replaced with a healthy one from a donor, such as a heart transplant or a lung transplant
  • liposuction - an operation to remove excess body fat
  • a hysterectomy - an operation to remove your womb (uterus)

If you need to have a general anaesthetic, it will be discussed with you before you have the surgery. You will meet your anaesthetist and plan your anaesthetic together.

Your anaesthetist will ask you about your general health and lifestyle including:

  • whether you have any allergies
  • whether you smoke or drink alcohol
  • whether you are taking any other medication

They will also be able to answer any questions that you have. You should be given clear instructions to follow before the operation, including whether or not you can eat anything in the hours leading up to it.

If you are unsure about any part of your anaesthetic, or your operation, check with your anaesthetist (or another healthcare professional who is treating you) that they are aware of your concerns.

Side effects

There are some common side effects from general anaesthetics. Your anaesthetist should discuss these with you before your surgery. Most side effects occur immediately after your operation and do not last long. Some possible side effects include:

  • feeling sick and vomiting after surgery - about one in three people may feel sick after an operation; this usually occurs straight away but some people may continue to feel sick for up to a day
  • shivering and feeling cold - about one in four people will experience this; shivering may last for 20 to 30 minutes after your operation 
  • confusion and memory loss - this is more common in elderly people and is usually only temporary; confusion can sometimes occur a few days or weeks after the operation
  • chest infection - this can affect one in five people who have abdominal surgery; it will make you feel feverish (hot and cold) and cause breathing difficulties  
  • bladder problems - men may have difficulty passing urine and women may leak urine; this is more common after a spinal or epidural anaesthetic
  • minor, temporary nerve damage - this can affect one in 100 people and causes numbness, tingling or pain that may get better in a few days or take several weeks to improve
  • dizziness - can occur after your operation but you will be given fluids to treat it
  • bruising and soreness - can develop in the area where you were injected or had a drip; it usually heals without treatment

During your operation, it may be necessary for you to have a tube inserted down your throat to help you breathe. Afterwards, this causes a sore throat in about two in five people. Around one in 20 people may have small cuts to their lips or tongue from the tube, and around one in 4,500 may have damage to their teeth.

Some people can experience "awareness" during surgery. This is very rare and is where you become conscious during the operation. Some estimates suggest that this happens to one person in every 1,000 anaesthetics given, but other estimates say it is only one person in every 14,000.

Only about a third of people who experience awareness feel any pain. Your anaesthetist will be on hand to adjust your medication so that you lose consciousness again.

Complications and risks

There are a number of more serious complications that are associated with general anaesthetics but, fortunately, they are very rare (occurring in less than one case for every 10,000 anaesthetics given). Complications include:

  • permanent nerve damage, causing paralysis or numbness
  • a serious allergic reaction to the anaesthetic (anaphylaxis)
  • death - this is extremely rare (there is approximately one death for every 100,000 general anaesthetics given)

Complications are more likely if:

  • you are having major surgery or emergency surgery
  • you have any other illnesses
  • you smoke
  • you are overweight

Your anaesthetist will discuss the risks with you before your operation. You may be advised to stop smoking or to lose weight, if doing so could reduce your risk of developing complications. In most cases, the benefits of being pain-free during an operation will outweigh the risks.

Anaesthetic is medication used to either numb a part of the body (local), or to put a patient to sleep (general) during surgery.
This is when your body has a severe allergic reaction to an allergen, such as food, which can be fatal. It is also called anaphylactic shock.
Blood supplies oxygen to the body and removes carbon dioxide. It is pumped around the body by the heart.
Your nerves are bundles of fibres that use chemical and electrical signals to pass information around your body.
Pain is an unpleasant physical or emotional feeling that your body produces as a warning sign that it has been damaged.
Vomiting is when you bring up the contents of your stomach through your mouth. 

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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