General anaesthesia

Expert reviewer, Dr Ahmed Almaki, Consultant Anaesthetist
Next review due June 2022

General anaesthesia is when medicines are used to make you unconscious during an operation or procedure. You don't feel pain or other sensations across your body while the effect lasts.

A middle aged woman is drinking tea

About general anaesthesia

The word ‘anaesthesia’ means 'loss of sensation'. A general anaesthetic puts you into a controlled state of unconsciousness.

Anaesthetists use a combination of medicines to:

  • make you unconscious
  • cause loss of sensation, so you don’t feel pain
  • relax your muscles

Having a procedure under general anaesthetic means you’ll stay unconscious throughout. Your anaesthetist will stay with you throughout your procedure . When the procedure is over they will stop the anaesthetic drugs, you’ll wake up and you won’t remember what happened.

Before your procedure, you’ll meet your anaesthetist to discuss your care. It will be tailored for you and the particular procedure you are having, so may differ from what’s described here.

Preparing for general anaesthesia

Your surgeon and anaesthetist will explain how to prepare for your procedure and general anaesthetic, including potential risks. You might find it helpful to prepare some questions to ask about the risks, benefits and alternatives to the procedure or type of anaesthetic.

It will help you recover if you are as fit as possible beforehand. You may want to talk to your GP or surgeon about steps you can take, particularly if you have a long-term medical condition such as diabetes, asthma or a heart condition.


If you smoke, try to stop smoking, as it can delay your recovery. It increases your risk of heart and breathing problems during and after surgery, delays wound healing and increases risk of wound infection.

Your weight

Being over or underweight can increase risk of complications. So it’s a good idea to try and lose some weight if you need to.

Eating and drinking

You may have specific advice to follow, depending on the procedure you’re having. Generally, patients are asked not to eat solids for six hours and fluids for 2 to 4 hours before a general anaesthetic. This is important because an anaesthetic can make you sick. Being sick while you’re unconscious is dangerous because you can’t cough, so fluid from your stomach could get into your lungs.

You can usually drink clear fluids (like water and black tea) up to two hours before your anaesthetic, but follow your anaesthetist or surgeon's advice. If you have any questions, just ask.


Unless you’ve been told not to, you can usually take your regular medicines with a sip of water early on the day of your procedure. If you’re in any doubt about what to take, ask.

At the hospital

Your anaesthetist will talk over what will happen before, during and after your procedure and anaesthetic, and discuss pain control afterwards. You need to understand what will happen so that you can give consent for it to go ahead. You may be asked to sign a consent form.

Your anaesthetist or nurse will ask about your medical history. It’s important to tell them about any allergies or health problems you have, or if you’ve had any problems during an anaesthetic before. Bring any medicines that you’re taking with you (including herbal remedies 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. They may need to put a tube in your throat to help you breathe while you’re under anaesthetic. If they have any difficulty placing this tube, there’s a possibility they may damage your teeth. But if they know in advance about any teeth that are vulnerable, they may be able to give them extra protection.

If you wear contact lenses, glasses, dentures or hearing aids, you’ll need to remove them. You also need to remove all make-up and nail varnish. Your skin colour and nail beds help to tell your anaesthetist that you’re getting enough oxygen.


These aren’t used so often these days, but if you feel anxious, you may be able to have a ‘pre-med’ half an hour to a couple of hours before your procedure. This can:

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

These ‘pre-med’ medicines can cause certain side-effects. This is partly why they are used less commonly now, unless there is a good reason.

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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 have a regional or local anaesthetic instead.

Regional anaesthetics completely block pain from an area of your body. They include spinal and epidural anaesthetics and nerve blocks.

Local anaesthesia numbs a small area of your body, such as around a cut that needs stitches.

You are awake during procedures done under regional or local anaesthesia. You may have 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 talk through the options for anaesthesia that are best for you.

What happens during general anaesthesia?

You usually have the initial anaesthetic medicines into one of your veins, through a fine, plastic tube (called a cannula). This is usually done in 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. The cannula means you won’t have to have a separate injection each time your anaesthetist needs to give you medicines or fluids.

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

When you’ve had the anaesthetic, you’ll ‘fall asleep’ and won’t wake up until after your procedure. When you are unconscious, your anaesthetist might put a tube in your mouth to help you breathe during your procedure. You will have more anaesthetic medicines during your procedure to make sure you stay unconscious.

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 afterwards
  • medicines to control your blood pressure
  • intravenous fluids (a drip), to keep you hydrated

Your pulse, blood pressure and breathing will be monitored by machines the whole time that you’re under anaesthetic. Your anaesthetist will be with you throughout the operation, watching the monitors and making any necessary adjustments. At the end of your operation, they’ll stop the anaesthetic medicines so you’ll begin to wake up.

What to expect afterwards

When you wake up, you’ll be in a recovery room next to the operating theatres. A specialist nurse will be there to look after you. 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 be attached to the monitors for a while after your procedure. Once your anaesthetist is happy that your breathing and heart rate are stable, 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. If it lasts longer, it is more likely to be due to recovery from the surgery you’ve had.

It’s really important that you rest until the effects of the anaesthetic have passed. Do tell your nurse if you’re in pain. Controlling pain will enable you to move more and that will help you to recover more quickly.

Other care you have will depend on the type of procedure you’ve had and your personal needs. Your nurse will remove your cannula and offer you something to eat or drink. If you’ve had a day-case procedure, you’ll usually be able to go home when you feel ready, but ask a friend or relative to collect you. It’s a good idea to have someone 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

General anaesthetics have some risks. These differ depending on individual circumstances, so ask your anaesthetist how they apply to you.

Side-effects are unwanted but mostly temporary effects that you may have after general anaesthesia. They include:

  • feeling sick and vomiting – steps are usually taken to prevent this
  • headache
  • dizziness
  • shivering
  • sore throat
  • tiredness and confusion
  • itching
  • blurred vision
  • backache
  • bruising where the cannula was put in

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 problems that can occur during or after a procedure. General anaesthesia does have some possible complications, but these are rare. They may be more likely if you already have a health condition, you smoke, you're overweight, or the surgery is major or being done in an emergency. But your anaesthetist will discuss any risks with you before the operation.

Allergic reaction

A serious allergic reaction is called anaphylaxis. It is very rare. Only one in every 10,000 people who have an anaesthetic have anaphylaxis. It may cause rash, itching, difficulty breathing and low blood pressure. Your anaesthetist will be there to treat you immediately if you have a reaction.

Peripheral nerve injury

Peripheral nerves run between your spinal cord and the rest of your body. During a procedure under anaesthetic, some nerves may be pressed on or squeezed. This could be because of your position during the procedure, or because of the surgical techniques or equipment used (rather than because of the anaesthetic).

Nerve damage can cause numbness, tingling, pain, warm or cold sensations, weakness and difficulty moving the affected area. Symptoms usually get better within a few months, although this will depend on the damage done and how bad it is. In around one in every 1,000 general anaesthesia operations, nerve damage is permanent. For more information, speak to your doctor.

Spinal cord injury

Your spinal cord carries information from your peripheral nerves to your brain. Spinal cord damage while under a general anaesthetic is very rare, but unfortunately is usually permanent. It’s 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.

Accidental awareness

Very rarely, people feel they are partly or completely awake and aware of what's happening while under general anaesthesia. This only happens in about one in every 20,000 anaesthetics. Two-thirds of these cases are when people are going under anaesthetic or coming round. Mostly people are aware for a very short time and usually report hearing someone talking or feeling something happening, such as something being put in their mouth. Even in the one third of cases where people are aware for a time during their operation, they don’t necessarily feel pain as they are being given strong painkillers. If you are at all concerned about this, do talk it over with your anaesthetist before your surgery. Always tell your anaesthetist after your operation if this has happened to you so that they can investigate why it happened and record it in your hospital notes.

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. Most often it is just some minor bruising or cuts in your lips. Tooth damage serious enough to need repairing only happens to about one in 4,500 people having a general anaesthetic. Your anaesthetist may look in your mouth before your anaesthetic to see if there are any issues. To try and prevent problems, have a dental check-up and any necessary dental work done beforehand.

Existing medical conditions getting worse

If you have had a stroke or heart attack in the past, you have a slightly increased risk of having another after your operation. If you have diabetes, asthma or high blood pressure, your condition will be closely monitored throughout and treated as necessary. Talk to your surgeon or anaesthetist if you are at all worried.

Dying under anaesthetic

This is extremely rare. Death during surgery is more likely to happen because a patient is very unwell or because of the risks of the surgery itself. It’s not possible to be definite but it’s thought that fewer than one in 100,000 people die as a result of having a general anaesthetic.

Frequently asked questions about general anaesthesia

  • There are some possible complications of having a general anaesthetic, but these are rare. They may be more likely if you already have a health condition, you smoke, you're overweight or the surgery you’re having is major or being done in an emergency. Your anaesthetist will discuss any risks with you before the operation. For more information see ‘Complications of general anaesthesia’.

  • After a general anaesthetic you may feel very tired. It’s really important that you rest until the effects of the anaesthetic have passed. You might find that you're not so coordinated or that it's difficult to think clearly. These effects might last for a few days. For more information see ‘Recovering from general anaesthesia’.

  • General anaesthesia makes you unconscious during an operation or procedure and you don’t feel pain or other sensations. Local anaesthesia numbs a small area of your body, such as around a cut that needs stitches, but you’re awake during the procedure. For more information see ‘What are the alternatives to general anaesthesia?’

  • Memory loss and confusion after a general anaesthetic are more common in older people but can happen at any age. Most people make a full recovery. You’re more likely to become confused after a general anaesthetic if you:

    • have had another operation recently
    • are very elderly
    • had a poor memory or dementia before your general anaesthetic
    • have difficulty walking
    • need glasses or a hearing aid
    • drink a lot of alcohol

    Some of the causes of confusion after a general anaesthetic can be easily treated. These include:

    • a chest, wound or urine infection – you may have antibiotics for this
    • poor pain control – your pain relief can be increased
    • not getting enough to eat 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 finding the cause and dealing with confusion. Your relatives can help by making sure you are wearing your glasses or hearing aid. 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). 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. 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 longer operations. It doesn’t seem to have anything to do with the type of anaesthetic you have. Ask your anaesthetist for more information.

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  • Reviewed by Graham Pembrey, Lead Editor, Bupa Health Content Team

    Expert reviewer Dr Ahmed Almaki, Consultant Anaesthetist

    Next review due June 2022