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General anaesthesia

General anaesthesia describes a reversible state brought about by particular drugs, in which you lose feeling and sensation. If you have a general anaesthetic, you’re in a state of controlled sleep (unconsciousness).

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

The word ‘anaesthesia’ comes from the Greek meaning absence or loss of sensation. Anaesthesia is one of the most important developments of modern medicine because it allows once unbearable medical procedures to be carried out with minimal discomfort.

An anaesthetic is a drug used to produce the absence or loss of sensation. For general anaesthesia, you will be given a combination of drugs to stop the messages from the nerves in your body being recognised by your brain. This means that when you’re under general anaesthesia, you will be in a state of controlled sleep (unconsciousness).

While you’re under general anaesthesia, you won’t feel pain and afterwards you won’t remember what happened during your procedure. The anaesthetic will wear off afterwards and you will regain consciousness.

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  • Preparation Preparing for general anaesthesia

    Your surgeon will explain how to prepare for your procedure. For example, if you smoke, you will be asked to stop as smoking increases your risk of getting a chest and wound infection, which can slow your recovery.

    You will be asked to follow fasting instructions. This means not eating or drinking, typically for about six hours beforehand. However, it’s important to follow your anaesthetist’s advice. You need to fast to ensure you have an empty stomach when you have a general anaesthetic so that you’re less likely to be sick. Vomiting while you’re unconscious can be dangerous because you can’t cough, so fluid from your stomach could get into your lungs.

    You will be asked about your medical history. You must tell your anaesthetist about any allergies that you have and whether you have asthma, hay fever or eczema. You should also tell him or her about any medicines that you’re taking (this includes herbal remedies as well as prescription and over-the-counter medicines).

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

    Your surgeon or 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, and you can help yourself by preparing 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, which you may be asked to do by signing a consent form.

    Your nurse will prepare you for your procedure and to go into the operating theatre. You may be given pre-medication (a ‘pre-med’), although these are rarely used now. The aim of pre-medication is to:

    • relieve severe anxiety
    • reduce pain after your procedure
    • reduce the risk of being sick after your procedure

    You may be asked to wear compression stockings to help prevent blood clots forming in the veins in your legs. You may need to have injections or tablets of anticlotting medicines as well as, or instead of, wearing compression stockings.

    When it’s time for your procedure, you will 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. This causes a sharp sensation, like an injection, which passes quickly. The cannula allows your anaesthetist to give you medicines and fluids without repeated injections.

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  • Alternatives What are the alternatives to general anaesthesia?

    General anaesthesia isn’t suitable for everyone and isn’t necessary for all procedures. Regional or local anaesthesia may be used instead. Regional anaesthesia completely blocks pain from an area of your body, for example, spinal or epidural anaesthesia. Local anaesthesia involves numbing only a small area of your body. You will stay awake during procedures done under these types of anaesthesia. You may also be given a sedative to relieve any anxiety you may have and to help you 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 drug through the cannula. Within a minute or so, you will fall asleep and won’t wake up until after your procedure. Alternatively, your anaesthetist may ask you to breathe in anaesthetic gases and oxygen through a mask. Your anaesthetist will stay with you throughout your procedure.

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

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

    While you’re under general anaesthesia, you will be connected to machines that monitor the activity of your heart and other body systems. Your anaesthetist will keep a close check on your heart rate, blood pressure and the amount of oxygen in your blood. You may have a tube in your mouth to help you breathe during your procedure.

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  • Aftercare What to expect afterwards

    Immediately after your procedure, you will be moved into a recovery room. As soon as the anaesthesia is stopped, you will begin to wake up. If you have a tube in your airway, this will be taken out as you wake up and you will be given oxygen to breathe through a mask. You will still be attached to the monitors but once your anaesthetist is happy with your progress, these will be disconnected and you will be taken back to your room or ward.

    You may feel sleepy or disorientated and you may have a sore throat, which could last for a couple of days. You may also feel sick, but you will probably have been given medicines to make this less likely.

    You will need to 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 individual needs. If you have had a day-case procedure, your nurse will remove your cannula and offer you something to eat or drink. You will usually be able to go home when you feel ready. You will need to arrange for someone to drive you home and should try to have a friend or relative stay with you for the first 24 hours.

  • Recovery Recovering from general anaesthesia

    General anaesthesia temporarily affects your co-ordination and reasoning skills, so you must not drive, drink alcohol, operate machinery or sign legal documents for 24 hours afterwards. If you’re in any doubt about driving, contact your motor insurer so that you’re aware of their recommendations, and always follow your anaesthetist’s advice.

  • Risks What are the risks of general anaesthesia?

    There are some risks associated with having general anaesthesia. We have not included the chance of these happening as they are specific to you and differ for every person. Ask your anaesthetist to explain how these risks 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.


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

    • A serious allergic reaction – this is called anaphylaxis. This 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 you may develop some awareness while under general anaesthesia. This can happen if you’re not getting enough of the anaesthetic drugs 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.
    • Dental or lip damage – this isn’t usually serious but it can happen if your anaesthetist inserts a tube into your mouth. About five in 100 people who have an anaesthetic may have damage to their lips and about one in 4,500 people who have an anaesthetic will have damage to their teeth that needs to be repaired.
    • There is a very small risk of dying during general anaesthesia although 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 rare – it’s not possible to be definite but it’s thought that about one in 100,000 people who have a general anaesthetic will die.
  • FAQs FAQs

    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 anaesthetic. 

    If these symptoms last for about a week after having a general anaesthetic, the condition is called ‘early POCD’. Early POCD affects about two in 10 people over the age of 60 having major surgery. However, this doesn’t include those who have heart surgery. This is because there is some evidence that the condition may be more likely to develop, and last for longer, after this type of procedure. Early POCD may not be severe and it may only be noticed by your close friends or family.

    Some people may still have a noticeable reduction in their mental ability, such as concentration, several months after surgery. This is called ‘late POCD’ and may occur in up to five in 100 people over 60 who have major surgery (again, this doesn’t include heart surgery). Late POCD may become permanent but it’s not known how often this happens.

    The exact reasons why you may develop POCD aren’t fully understood at present. However, it appears to be more likely after heart surgery.

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


    Memory loss and confusion after general anaesthesia are 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 become confused 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 over 60
    • are generally unwell
    • have poor memory or dementia
    • 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 in passing urine – you may need a catheter placed in your bladder

    Memory loss and confusion can be upsetting for you and for your friends and relatives, but it's important to 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.

    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 called 'awareness under general anaesthesia'.


    Being aware of what is happening while under general anaesthesia is rare. A survey published in 2007 of over 80,000 people reported that only one in 14,000 people developed awareness when having a general anaesthetic. Most people who experience awareness during anaesthesia don't have any pain, but can see, hear and may be able to feel the tube in their throat. Some people may have memories of the recovery room and these are sometimes confused with the operating theatre. 

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

    • open heart surgery
    • surgery after a major accident
    • a caesarean under general anaesthesia

    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 control your level of anaesthesia by monitoring your condition throughout the procedure and the amount of the anaesthetic drug in your body.

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

  • Resources Resources

    Further information


    • General anaesthesia – general considerations. eMedicine., published August 2011
    • Anaesthesia explained. The Royal College of Anaesthetists., published May 2008
    • Risks associated with your anaesthetic. The Royal College of Anaesthetists., published October 2009
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