General anaesthesia

Expert reviewer, Dr Ahmed Almaki, Consultant Anaesthetist
Next review due February 2025

General anaesthesia is when you have medicines to make you temporarily unconscious during an operation. You don't feel pain or other sensations while the effect lasts.

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About general anaesthesia

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

A general anaesthetic is usually several medicines used together to:

  • make you unconscious
  • stop you feeling pain
  • stop you remembering what happened
  • You may also have medicines that relax your muscles. You’re likely to need these if you’re having an operation on your abdomen (tummy) or chest.

    Having a general anaesthetic means you’ll be unconscious all the way through your operation. Your anaesthetist will stay with you throughout your procedure. When your operation is finished, they’ll stop the anaesthetic drugs. You’ll wake up and you won’t remember what happened.

    Before your procedure, you’ll meet your anaesthetist or specialist preoperative nurse to discuss your care. It might be different from what we've described here because it will be designed to meet your individual needs.

Preparing for general anaesthesia

Your surgeon and anaesthetist will explain how to prepare for your operation and the general anaesthetic. That includes talking about the potential risks. You might find it helpful to prepare some questions to ask about the procedure or the anaesthetic.

It will help your recovery if you’re as fit and as well as possible beforehand. These are the main things that can help you to do that.

  • If you have a long-term health condition such as diabetes or high blood pressure, it can affect how well you recover. It’s a good idea to talk to your GP or nurse about how you can be as fit as possible for your surgery. That’s likely to mean getting any health conditions as well controlled as possible.
  • If you smoke, try to stop. Smoking makes it more likely you’ll get complications, and it can slow down your healing and recovery.
  • Being over or underweight can increase risk of complications too. So, it’s a good idea to reach a healthy weight if you need to.
  • It’s a good idea to follow a healthy lifestyle in the weeks and months before your operation. Being active and eating healthily will help you recover well.
  • If you have any crowns or loose teeth, it’s a good idea to go to the dentist to have these fixed. If your teeth are in good condition, they’re less likely to be damaged during surgery.

If you’re having a major operation such as heart or brain surgery, you’ll usually be asked to go to a pre-assessment clinic a few weeks before. At the clinic you’ll probably see your anaesthetist and have some tests and checks done. These are to see what your general health is like. If you’re taking any regular medicines including over-the-counter or herbal medicines, tell the staff at the clinic.

On the day of your operation

Having a general anaesthetic can sometimes make you sick. If that happens while you’re unconscious, it can be dangerous. So, your stomach needs to be empty before your operation.

You’ll be given information about when to stop eating and drinking. The advice is usually not to eat anything in the six hours before surgery. You should be able to drink clear fluids such as water or black tea or coffee up to two hours before your operation.

If you’ve been asked to take your usual medication before your operation, you can take it with a small sip of water.

Follow your anaesthetist or surgeon's advice and if you have any questions, just ask.

At the hospital

Your nurse or surgeon will talk to you about what will happen, including any pain you might have. If you’re unsure about anything, just ask. No question is too small. Being fully informed will help you feel more at ease and will allow you to give your consent for the procedure to go ahead. You may be asked to do this by signing a consent form.

There are some important things to do on the day of your operation.

  • Tell your anaesthetist and nurse about any allergies or health conditions you have.
  • If you’ve had a general anaesthetic before and you had any problems during or after it, tell your anaesthetist. That includes being sick afterwards.
  • If there’s anything about the anaesthetic or operation that you’re really worried about, tell your anaesthetist.
  • Tell your anaesthetist about any medicines you’re taking and any you’ve taken that day. That includes any alcohol or drugs because these can affect how anaesthetic medicines work.
  • Take off any make-up and nail varnish. Your skin and lip colour help to tell your anaesthetist that you’re getting enough oxygen. Nail varnish and false nails can interfere with equipment that monitors your oxygen levels.
  • If you wear contact lenses, glasses or hearing aids, you’ll need to remove them when you get to the anaesthetic room.
  • Tell your anaesthetist about any loose teeth or crowns and take out any dentures if you have them.


Pre-medication is one or more medicines given to you just before your operation. Not everyone has them, but they’re normally given one or two hours before a procedure. Pre-medication can include:

  • medicines to reduce the acid in your stomach
  • anti-sickness medicines
  • painkillers to help you during and after your operation

If you’re very anxious about the operation, you may also be given medicines to help you relax.

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What happens during general anaesthesia?

You’ll probably have your anaesthetic in a room next to the operating theatre. When you get there, your anaesthetist or operating assistant will go through some safety checks with you. These include checking your name, asking if you have any allergies and what operation you’re having.

You’ll be connected to equipment that monitors your heart rate, blood pressure and oxygen levels during the operation. You’ll have a small plastic tube called a cannula put into the back of your hand or arm.

There are two main ways to have anaesthetic medicines:

  • breathed in through a face mask as an anaesthetic gas with oxygen
  • injected into your vein through the cannula

You might have one or both of these. Whichever way you have the anaesthetic, it will start to work within a minute or two. You’ll then ‘fall asleep’ and won’t wake up until after your procedure.

When you’re unconscious, your anaesthetist might put a tube in your mouth to help you breathe. You‘ll be given more anaesthetic medicines during the operation to make sure you stay unconscious.

During the operation, your anaesthetist and nurses will make sure you’re kept warm enough. They’ll also check the position you’re lying in to prevent any damage to your joints, skin or nerves.

Your anaesthetist may also give you:

  • 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 anaesthetist will be with you throughout the operation, watching the monitors and making any changes needed. At the end of your procedure, they’ll start the process of waking you up by stopping the anaesthetic medicines.

What to expect after general anaesthesia

When you wake up, you’ll be in a recovery room next to the operating theatre. A specialist nurse will be there to look after you. They’ll check on you regularly. If you feel sick or have pain, they will give you medicines to ease your symptoms.

You may have oxygen to breathe through a mask and fluids through the cannula in your arm. You’ll also be attached to heart, blood pressure and oxygen monitors for a while after your procedure. You’ll be taken back to your ward when your anaesthetist is happy that you’re recovering well.

Tell your nurse if you’re in pain. Getting your pain under control will help you to move more which can help with your recovery.

Other care you have will depend on the type of procedure you’ve had and your personal needs. When your nurse thinks that you’re ready, you can have something to eat or drink.

The effects of the anaesthetic can last for 24 hours, or longer if you have had a major operation. When you can go home will depend on the operation you’ve had and how well you’re recovering. If you’ve had a day-case procedure, you’ll usually be able to go home when you’ve recovered and feel ready on the same day. Make sure someone can take you home and stay with you for a day or so while the anaesthetic wears off.

Recovering from general anaesthesia

Having a general anaesthetic 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.

You may feel tired 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 other things, such as lack of sleep, anxiety or not being able to eat or drink properly. The healing process after a big operation can leave you feeling very tired.

Side-effects of general anaesthesia

Side-effects are unwanted but mostly temporary effects of the anaesthetic. They include:

  • feeling sick and being sick
  • headache
  • feeling thirsty
  • shivering
  • sore throat
  • backache
  • bruising

If you’re worried about any side-effects or they don't get better, contact your hospital.

Complications of general anaesthesia

General anaesthetics have some risks. These are different for everyone, so ask your anaesthetist how they apply to you.

Complications are problems that can occur during or after a procedure. General anaesthesia complications are rare but can be serious. They may be more likely if:

  • you already have a long-term health condition
  • you smoke
  • you're overweight
  • the surgery is major or being done in an emergency

These are some of the main complications of general anaesthesia.

  • A severe allergic reaction called anaphylaxis is rare but if it happens, it can be life-threatening. It can cause a rash, itching, difficulty breathing and low blood pressure. Your anaesthetist will treat you immediately if you have a reaction.
  • Nerve damage can happen if you’re in the same position for too long during the operation. Your nerves can get squashed and that can damage them. It can cause numbness and tingling, pain, warm or cold sensations and weakness. Symptoms usually get better within a few months. But for a few people the damage is permanent.
  • Damage to your teeth or mouth can happen when the anaesthetist is keeping your airway open, so that you can breathe during the operation. You can get small injuries to your lips, mouth or tongue. Sometimes teeth and crowns can be chipped, broken or knocked out.
  • Being confused or having memory problems can happen after general anaesthesia. Some people may develop delirium. This type of complication can be caused by many things, including an infection or the side-effects of medicines. It usually gets better with treatment after a few days. Postoperative cognitive dysfunction is when you have trouble with more complicated mental tasks. It can develop over weeks and months. Most people make a full recovery.

Some people worry about being ‘awake’ during an anaesthetic or being aware of what is going on during the operation. This does happen, but it’s very rare. It happens in about one in every 20,000 anaesthetics. It might mean being aware of talking or having something put in your mouth. A few people are aware of being unable to move or feel pain. It usually lasts for a few minutes, but it can be very distressing. Always tell your anaesthetist after your operation if this has happened to you.

What are the alternatives to general anaesthesia?

General anaesthesia isn’t right for everyone. You may have a regional or local anaesthetic instead.

  • Regional anaesthetics completely block pain from a large area of your body. They include spinal and epidural anaesthetics and nerve blocks.
  • Local anaesthesia numbs a small area of your body – for example, the area around a tooth that is being taken out.

You’re awake during procedures done using regional or local anaesthesia. Some people choose to have a sedative as well to help them relax. How much you remember about the procedure afterwards varies from person to person. Your anaesthetist will talk to you about the different options and which might be best for you.

Frequently asked questions about general anaesthesia

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  • Reviewed by Sarah Smith, Freelance Health Editor and Michelle Harrison, Lead Editor at Bupa
    Expert reviewer, Dr Ahmed Almaki, Consultant Anaesthetist
    Next review due February 2025