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General anaesthesia

The word ‘anaesthesia’ comes from the Greek language and means 'loss of sensation'. General anaesthesia is when medicines are used to send you to sleep and stop you feeling pain and other sensations. Anaesthesia is one of the most important developments of modern medicine. It means that medical procedures that would be unbearable without it can be carried out with minimal discomfort.

General anaesthesia allows you to have medical procedures with as little pain and distress as possible. When you have a general anaesthetic, you’re in controlled state of sleep (unconsciousness).

General anaesthesia uses a combination of medicines to:

  • provide pain relief
  • produce a loss of feeling and block the messages that pass along your nerves to your brain
  • relax your muscles (in some procedures)

If you have a procedure under general anaesthetic, once it’s finished the anaesthetic will wear off and you’ll wake up. You won’t remember what happened during your procedure.

You will meet the anaesthetist (a doctor who specialises in pain management and delivering medicines for surgical procedures) to discuss your care. It may differ from what is described here as it will be adapted to suit you.

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  • Preparation Preparing for general anaesthesia

    Your surgeon and anaesthetist will explain how to prepare for your procedure. For example, if you smoke, you will be asked to stop. This is important because smoking increases your risk of getting a chest or wound infection, which will mean it takes you longer to recover afterwards.

    An anaesthetic can make you sick so it's important that you don't eat anything for six hours before you’re given it.

    If you're sick while you’re unconscious, it can be dangerous because you can’t cough, so fluid from your stomach could get into your lungs. You can drink clear fluids up to two hours before you have the anaesthetic. It may sound obvious, but clear fluids are ones you can see through, such as water or tea without milk. Anything with milk in it counts as food. Follow your anaesthetist and doctor's advice. If you have any questions, just ask.

    Your anaesthetist or nurse will ask you about your medical history. You must tell them about any allergies that you have and any health problems. It's also important to mention any medicines that you’re taking (this includes herbal remedies as well as prescription and over-the-counter medicines).

    Your anaesthetist may need to put a tube in your throat to help you breathe while you’re under general anaesthesia. Tell your anaesthetist if you have any dental crowns, bridges or loose teeth. If you wear contact lenses, glasses, dentures or hearing aids, you will need to remove them before you have a general anaesthetic.

    Your surgeon and anaesthetist will discuss with you what will happen before, during and after your procedure, and any pain you might have. This is your opportunity to understand what will happen. You might like to prepare some questions to ask about the risks, benefits and any alternatives. This will help you to be informed, so you can give your consent for the procedure to go ahead. You may be asked to do this by signing a consent form.

    Your nurse will prepare you for your procedure and go to the operating theatre with you. If you feel anxious about your procedure, you may be able to have pre-medication (a ‘pre-med’). The aim of pre-medication is to:

    •  relieve anxiety and help you to relax
    • reduce pain after your procedure
    • reduce the risk of being sick after your procedure

    When it’s time for your procedure, you’ll be taken to the anaesthetic room next to the operating theatre. Your anaesthetist will insert a fine, plastic tube (called a cannula) into one of your veins, usually on the back of your hand or arm. This causes a sharp sensation, like an injection, but it passes quickly. Having a cannula means you won’t have to have a separate injection each time your anaesthetist needs to give you medicines or fluids.

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  • Alternatives What are the alternatives to general anaesthesia?

    General anaesthesia isn’t suitable for everyone nor is it always necessary for a procedure. You may be able to have regional or local anaesthesia instead.

    • Regional anaesthesia, such as a spinal, epidural or nerve block, completely blocks pain from an area of your body.
    • Local anaesthesia involves numbing only a small area of your body.

    You will stay awake during procedures done under regional or local anaesthesia. You may also be given a sedative to relieve any anxiety and help you to relax. How much you will remember about the procedure afterwards varies from person to person. Your anaesthetist will discuss with you which type of anaesthesia is most suitable for you.

  • The procedure What happens during general anaesthesia?

    Your anaesthetist will usually give you the anaesthetic medicine through a cannula (thin, plastic tube) into a vein. Within a minute or so, you will fall asleep and won’t wake up until after your procedure. Alternatively (or as well as), your anaesthetist may ask you to breathe in anaesthetic gases and oxygen through a mask. Once you’re asleep you may have a tube placed in your mouth to help you breathe during your procedure.

    As well as giving you more anaesthetic medicines while you’re asleep, your anaesthetist may give you the following.

    • Oxygen (via a tube in your mouth).
    • Strong painkillers to prevent pain during and after your procedure.
    • Medicines to relax your muscles, so that your surgeon can operate more easily.
    • Antibiotics to prevent infection.
    • Anti-sickness medicines to prevent you from feeling sick after the procedure.
    • Medicines to control your blood pressure.

    You will be connected to machines the whole time that you’re under anaesthesia. These monitor the activity of your heart and other systems in your body. Your anaesthetist will be with you throughout the operation and will watch the monitors and make any necessary adjustments. At the end of your operation the anaesthetic medicines will be turned off and you will begin to wake up.

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  • Aftercare What to expect afterwards

    Immediately after your procedure, you will be moved into a recovery room where you’ll gradually wake up. If you still have a tube in your mouth, this will be taken out once you’re fully awake. You will be given oxygen to breathe through a mask and may receive fluids through the cannula in your arm. You’ll still be attached to the monitors for a while after your procedure. Once your anaesthetist is happy that certain things, such as your breathing and heart rate are returning to normal, these will be disconnected. You will then be taken back to your room or ward.

    You may feel sleepy or disorientated and have a sore throat, which could last a few days. You may also feel sick, although you’ll probably have been given medicines to make this less likely.

    It’s really important that you rest until the effects of the anaesthetic have passed. You may need further pain relief to help with any discomfort as the anaesthetic wears off.

    The care you receive after this will depend on the type of procedure you have had and your personal needs. If you have had a day-case procedure, your nurse will remove your cannula and offer you something to eat or drink. You’ll usually be able to go home when you feel ready but make sure someone can go with you. And ask someone to stay with you for a day or so while the anaesthetic wears off.

  • Recovery Recovering from general anaesthesia

    Having a general anaesthetic affects everyone differently, so don’t worry if you don’t feel yourself for a while afterwards. You might find that you're not so coordinated or that it's difficult to think clearly but this should pass within 24 hours. The longer your operation, the longer the recovery from the anaesthetic is likely to be. In the meantime, don't drive, drink alcohol, operate machinery or sign any important documents. If you don't feel like you're back to normal after this time, contact your doctor.
  • Risks What are the risks of general anaesthesia?

    There are some risks associated with having general anaesthesia. These are specific to you and differ for everyone depending on their circumstances, so ask your anaesthetist to explain how they apply to you.


    Side-effects are the unwanted but mostly temporary effects you may get after having general anaesthesia. Side-effects of general anaesthesia include:

    • feeling sick and vomiting
    • shivering
    • a sore throat
    • a headache
    • feeling tired and confused
    • itching
    • problems with your eyesight (this is rare)

    These side-effects usually last for only a few hours, but occasionally they can continue for several days. If the symptoms don't get better, speak to your doctor.


    Complications are when problems occur during or after a procedure. Complications of general anaesthesia can include the following.

    • A serious allergic reaction – this is called anaphylaxis. It may be triggered by the anaesthesia or another medicine, for example antibiotics, but it’s very rare. Anaphylaxis is thought to affect between one in 10,000 and one in 20,000 people who have an anaesthetic. Your anaesthetist will be on hand to treat you immediately if you do develop anaphylaxis.
    • Very rarely people feel they are partly or completely awake and aware of what's happening while under general anaesthesia. It can happen if you’re not receiving enough of the anaesthetic medicines to make sure you stay unconscious. Most people who develop awareness during their procedure don’t feel any pain but it can be upsetting. See our frequently asked questions for more information.
    • Damage to your teeth, lips or tongue – this isn’t usually serious but it can happen if your anaesthetist inserts a tube into your mouth. About one in 20 people who have a general anaesthetic may have minor damage to their lips, such as a cut or bruise. About one in 4,500 people who have a general anaesthetic will have damage to their teeth that needs to be repaired.
    • There is a very small risk of dying during general anaesthesia. However, it can be difficult to tell whether this is because of the anaesthetic or another risk of your procedure. It’s important to remember that the risk is very small. It’s not possible to be definite but it’s thought that about one in 100,000 people who have a general anaesthetic die.
  • FAQs FAQs

    Will I be aware of what is happening if I have general anaesthesia?


    It's possible, although very rare, that you may develop some awareness during your procedure if you don’t receive enough of the anaesthetic drugs. This is when you partly or fully wake up and is called 'accidental awareness under general anaesthesia'.


    It’s rare to be aware of what is happening while you’re under general anaesthesia. A survey published in 2014 reported that only about one in 19,000 patients developed awareness when having a general anaesthetic. Most people who feel awareness during anaesthesia don't have any pain, but may see, hear and even feel the tube in their throat. Some people may have memories of the recovery room and these are sometimes confused with the operating theatre – this isn’t awareness.

    The exact reasons why you may develop awareness under general anaesthesia aren't fully understood at present. Awareness appears to be more likely if you're having:

    • open heart surgery
    • surgery after a major accident
    • a caesarean

    Awareness may be more likely because your anaesthetist may have used less of the anaesthetic drug in these types of surgery.

    You may also be at a greater risk of awareness if you’re very ill or if you’re taking certain medicines.

    Your anaesthetist will do everything possible to keep you asleep. They do this by monitoring your condition throughout the procedure and controlling the amount of the anaesthetic drug in your body appropriately.

    If you remember anything from your procedure, it’s important that you talk to your anaesthetist as soon as possible.

    What is the risk of memory loss or confusion after general anaesthesia?


    Memory loss and confusion after general anaesthesia are more common in older people but can happen at any age. Most people make a full recovery within a few days.


    After having a general anaesthetic, you may feel confused or have trouble with your memory for some time afterwards. Sometimes you may not be able to remember things, such as your name or why you're in hospital. You may behave differently from usual, for example, you may be aggressive, anxious or withdrawn.

    You’re more likely to develop confusion after your general anaesthetic if you:

    •  are older
    • have had another operation recently
    • had a poor memory or dementia before you had a general anaesthetic
    • have difficulty walking
    • drink a lot of alcohol

    There are other causes of confusion after a general anaesthetic that can be treated easily, including:

    • a chest, wound or urine infection – you may be given antibiotics
    • poor pain control – your pain relief can be increased
    • not getting enough to eat and/or drink – your fluid and nutrition can be increased
    • difficulty going to the toilet – you may need to take medicines for constipation

    Memory loss and confusion can be upsetting for you and for your friends and relatives, which is understandable. However, remember that the staff treating and caring for you will be used to dealing with it. Most people who have confusion after general anaesthesia make a full recovery within a few days.

    I have heard about post-operative cognitive dysfunction caused by general anaesthesia – what is this?


    Some people who become confused after a general anaesthetic don't recover fully and this is called post-operative cognitive dysfunction (POCD).


    Memory loss and confusion after general anaesthesia are common. Most people who have confusion after general anaesthesia get better within a few days. However, some people don't recover fully and find that their memory, concentration and/or attention are no longer as they were before having the general anaesthetic.

    This is called POCD and it affects about one in 10 patients in the first three months after their operation. After a year, only one in 100 patients still have it. You may not notice anything when you first come out of hospital and only realise when you start doing your usual daily tasks again. It may only be your close friends or family who see you're having difficulties.

    POCD tends to get better as your body heals after your operation but it can take months or years. In some people it can be permanent.

    The exact reasons why you may develop POCD aren’t fully understood at present. However, it appears to be more likely after open heart surgery and after longer operations. Ask your anaesthetist for more information.

  • Resources Resources

    Further information


    • You and your anaesthetic. Royal College of Anaesthetists., published 2014
    • General anesthesia. Medscape., published 10 September 2013
    • Important complications of anaesthesia. PatientPlus., published 25 June 2014
    • Patient information leaflets – complete series 2014. Royal College of Anaesthetists., published 2014
    • General anaesthesia. PatientPlus., published 18 February 2011
    • Risks associated with your anaesthetic. Royal College of Anaesthetists., published 2014
    • Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press., accessed 3 November 2014
    • Local and regional anesthesia. Medscape., published 3 June 2013
    • Accidental awareness during general anaesthesia in the United Kingdom and Ireland. Royal College of Anaesthetists., published September 2014
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