General anaesthesia

Expert reviewer, Dr Daniel Martin, Senior Lecturer & Honorary Consultant, Perioperative & Critical Care Medicine, University College London
Next review due October 2019

General anaesthesia is when medicines are used to send you to sleep and stop you feeling pain and other sensations. It allows you to have medical procedures with as little pain and distress as possible.

Middle-aged woman drinking tea

About general anaesthesia

The word ‘anaesthesia’ comes from the Greek language and means 'loss of sensation'. When you have a general anaesthetic, you’re in controlled state of sleep (unconsciousness).

General anaesthesia uses a combination of medicines to:

  • make you sleep (be unconscious)
  • give you pain relief through a loss of sensation
  • relax your muscles

If you have a procedure under general anaesthetic, you’ll stay asleep until it’s finished and the anaesthetic wears off; then you’ll wake up. Your anaesthetist will stay with you throughout your procedure. You won’t remember what happened during the procedure.

You’ll meet your anaesthetist to discuss your care. It may differ from what’s described here as it will be adapted to suit you.

Preparing for general anaesthesia

Before your procedure

Your surgeon and anaesthetist will explain how to prepare for your procedure and general anaesthesia. For example, if you smoke, you should consider quitting. This is because it increases your risk of heart and breathing problems during and after your operation, and of getting a wound infection. This means it would take you longer to recover afterwards. If you’re overweight, it’s a good idea to try and lose some weight. Being overweight puts you at greater risk of complications.

Eating and drinking

It’s probably best not to drink any alcohol at least 24 hours before having a general anaesthetic but follow any advice from your hospital.

An anaesthetic can make you sick so it's important that you don't eat or drink anything for six hours before a general anaesthetic. 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 (like water and black tea) up to two hours before your anaesthetic. Follow your anaesthetist or surgeon's advice. If you have any questions, just ask.


If you’re taking medicines, you can usually take your normal dose with a sip of water early in the morning on the day of your procedure. But don’t take any if your anaesthetist or surgeon has told you not to. If you’re in any doubt about what medicines to take or not take, ask your anaesthetist or somebody in your healthcare team at hospital.

At the hospital

Your surgeon and anaesthetist will discuss with you what will happen before, during and after your procedure and anaesthesia, and any pain you might subsequently have. This is your opportunity to understand what will happen, so you can give your consent for it to go ahead. You might find it helpful to prepare some questions to ask about the risks, benefits and alternatives to the procedure and anaesthesia. You may be asked to sign a consent form.

Your anaesthetist or nurse will ask you about your medical history. It’s important to tell them about any allergies you have and any health problems, and if you’ve had any problems during an anaesthetic before. You should also mention any medicines that you’re taking (including herbal remedies as well as prescription and over-the-counter medicines). If you’ve had any alcohol or taken any drugs, tell them about this too.

Let your anaesthetist know if you have any dental crowns, bridges or loose teeth. This is because they may need to put a tube in your throat to help you breathe while you’re under general anaesthesia. If they have any difficulty placing this tube, there’s a possibility they may damage your teeth. If you wear contact lenses, glasses, dentures or hearing aids, you’ll need to remove them.


If you feel anxious about your procedure, you may be able to have pre-medication (a ‘pre-med’) half an hour to a couple of hours before. This can:

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

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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 best for you.

What happens during general anaesthesia

Your anaesthetist will usually give you the anaesthetic medicines through a a fine, plastic tube (called a cannula) into one of your veins. When it’s time for your procedure, you’ll be taken to the anaesthetic room next to the operating theatre. Your anaesthetist will usually put the cannula into a vein on the back of your hand or arm. This may feel sharp, like an injection, but they might use local anaesthetic to ease this. The cannula means you won’t have to have a separate injection each time your anaesthetist needs to give you medicines or fluids.

Sometimes, your anaesthetist may ask you to breathe in anaesthetic gases and oxygen through a mask as well as or instead of having a cannula.

Once your anaesthetist gives you the anaesthetic medicines, you’ll fall asleep and won’t wake up until after your procedure. When you’ve fallen asleep, your anaesthetist might put a tube in your mouth to help you breathe during your procedure. You’ll be given more anaesthetic medicines during your procedure to make sure you stay asleep.

Your anaesthetist may also give you:

  • 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
  • intravenous fluids (a drip) to keep you hydrated

You’ll 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, although some equipment does this automatically. At the end of your operation, they’ll turn off the anaesthetic medicines and you’ll begin to wake up.

What to expect afterwards

Immediately after your procedure, you’ll be moved to a recovery room where you’ll gradually wake up. A specialist nurse will care you for while you’re in recovery. If you still have a tube in your mouth, your anaesthetist will take it out once you’re fully awake. They’ll give you oxygen to breathe through a mask and 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, they’ll disconnect the monitors. You’ll then be taken back to your room or ward.

You may feel sleepy or even exhausted after a general anaesthetic, and this might last for a few days. 

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’ve had and your personal needs. If you’ve 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 ask a friend or relative to go with you. It’s a good idea for them to stay with you for a day or so while the anaesthetic wears off.

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. Sometimes, it can really take it out of you. You might find that you're not so coordinated or that it's difficult to think clearly. This should pass within 24 hours. In the meantime, don't drive, drink alcohol, operate machinery or sign anything important.

Side-effects 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 how they apply to you.

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

  • feeling sick and vomiting – although steps are usually taken to prevent this
  • a headache
  • feeling dizzy
  • shivering
  • a sore throat
  • feeling tired and confused
  • feeling itchy
  • blurred vision
  • backache
  • bruising where the cannula was put in

These side-effects usually only last for a few hours, but occasionally they can last for several days. If they don't get better, contact your hospital.

Complications of general anaesthesia

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

  • A serious allergic reaction, which is called anaphylaxis. It may be triggered by the anaesthetic but it’s very rare. One or two people in every 20,000 who have an anaesthetic are estimated to get anaphylaxis. Your anaesthetist will be on hand to treat you immediately if you do develop the condition.
  • Peripheral nerve injury. Peripheral nerves are nerves that run between your spinal cord and the rest of your body. During a procedure under general anaesthetic, your nerves may become squeezed or pressed down on. This could be because of the way you’re positioned during the procedure, or because of the surgical techniques or equipment used. If your peripheral nerves are damaged, you may feel numbness, tingling, pain, or even warm or cold sensations. You may get weakness in the affected area or be unable to move it afterwards. Symptoms usually get better within a few months, although this will depend on the damage done and how bad your symptoms are. It’s uncommon, but sometimes the damage can be permanent. For more information, speak to your doctor.
  • Spinal cord injury. Your spinal cord is part of your central nervous system (CNS) – it carries information from your peripheral nerves to your brain. It’s very rare, but possible that your spinal cord could be damaged while under general anaesthesia. This damage is usually permanent and most often caused by a lack of blood getting to your spinal cord. This may be because you have low blood pressure, a blood clot in the vessels supplying blood to your spinal cord, or narrowing of your blood vessels because they’ve been stretched or compressed.
  • Awareness. Very rarely, people feel they are partly or completely awake and aware of what's happening while under general anaesthesia. See FAQ: Will I be aware? for more information.
  • Damage to your teeth, lips or tongue – this isn’t usually serious but it can happen if your anaesthetist puts a tube into your mouth. You might just have some minor bruising or cuts in your lips, but you could have some damage to your teeth. This happens to about one in 4,500 people who have a general anaesthetic.
  • Dying during general anaesthesia. This risk is very small and it can be difficult to tell whether it’s because of the anaesthetic or another risk of your procedure. It’s not possible to be definite but it’s thought that less than one in 100,000 people die as a result of having a general anaesthetic.
  • If you have a pre-existing health condition, it may get worse as a result of having an operation under general anaesthesia.

Frequently asked questions

  • It's possible, although very rare, that you might become aware of things during your procedure if you don’t receive enough of the anaesthetic medicines. You could partly or fully wake up and this is called 'accidental awareness under general anaesthesia'.

    More information

    Most studies suggest that one or two people in every 1,000 who have a general anaesthetic develop awareness when having a general anaesthetic. Most people don't have any pain, but may see, hear and even feel the tube in their throat. Some people who have memories of the recovery room confuse these with the operating theatre but this isn’t awareness. 

    Doctors don’t yet know the exact reasons why some people develop awareness under general anaesthesia. But they think it’s more likely to happen if you're having an operation where a lower level of anaesthetic is used. Such operations include:

    • open heart surgery
    • surgery after a major accident
    • a caesarean
    • surgery on your chest 

    Your risk can also increase if you’re very ill or if you’re taking some types of medicines. Ask your anaesthetist for more information on which ones. They’ll do everything possible to keep you asleep. They’ll monitor your condition throughout the procedure and control the anaesthetic medicine going into your body to make sure you get the right amount.

    If you do remember anything from your procedure, tell your anaesthetist as soon as possible.

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

    More information

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

    You’re more likely to become confused after a general anaesthetic if you: 

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

    Other things that can cause confusion after a general anaesthetic, and which can be treated easily, include: 

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

    The staff treating and caring for you will be used to dealing with confusion and most people make a full recovery within a few days. But sometimes it can take weeks or even months.

  • Some people notice that they’re confused some time after their operation rather than immediately. This is called post-operative cognitive dysfunction (POCD). 

    More information

    Memory loss and confusion after general anaesthesia are common and most people get better within a few days. But some people notice this happens later and that their memory, concentration and/or attention are no longer as they were before having the general anaesthetic.

    This is called POCD and it’s estimated to affect 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 might not notice anything at first and only realise when you start getting back to normal again. It may only be your close friends or family who notice you're having difficulties. 

    POCD tends to get better as your body heals after your operation but it can take months or years. Some people never fully get back to normal.

    Doctors don’t yet know the exact reasons why some people get POCD. But it seems to be more likely after open heart surgery and after longer operations. Ask your anaesthetist for more information.

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Related information

    • General anesthesia. Medscape., updated 30 November 2015
    • Important complications of anaesthesia. PatientPlus., last checked 25 June 2014
    • General anaesthesia. PatientPlus., last checked 4 June 2015
    • Anaesthesia explained. The Royal College of Anaesthetists., published November 2015
    • Depth of anaesthesia monitors – bispectral index (BIS), E-entropy and narcotrend-compact M. National Institute for Health and Care Excellence (NICE), November 2012.
    • Checketts MR, Alladi R, Ferguson K, et al. Recommendations for standards of monitoring during anaesthesia and recovery 2015: Association of Anaesthetists of Great Britain and Ireland. Anaesthesia 2016; 71:85–93. doi:10.1111/anae.13316  
    • You and your anaesthetic. The Royal College of Anaesthetists., published 2014
    • Personal communication, Dr Daniel Martin, Senior Lecturer & Honorary Consultant, Perioperative & Critical Care Medicine, University College London, 7 October 2016
    • Risks associated with your anaesthetic – complete series 2013. The Royal College of Anaesthetists., published 2013
    • Risks associated with your anaesthetic. Royal College of Anaesthetists., published 2017
  • Reviewed by Rachael Mayfield-Blake, Bupa Health Content Team, October 2016
    Expert reviewer, Dr Daniel Martin, Senior Lecturer & Honorary Consultant, Perioperative & Critical Care Medicine, University College London
    Next review due October 2019

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