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There are different types of anaesthesia, ranging from an injection of a local anaesthetic to numb one small area (such as a finger or tooth) to general anaesthesia with temporary complete loss of consciousness. Apart from local anaesthesia, the different types of anaesthesia are usually provided by specialist doctors called anaesthetists, usually supported by a specialist team of nurses and technicians.

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What is anaesthesia?

Anaesthesia means 'loss of sensation'. It can involve a local injection of a medicine to numb a small part of the body, such as a finger or around a tooth. It can also involve using a medicine that causes unconsciousness (general anaesthesia). The different types of anaesthesia are:

  • Local anaesthesia.

  • Regional anaesthesia:

    • Spinal anaesthesia.

    • Epidural anaesthesia.

    • Nerve block.

  • Sedation.

  • General anaesthesia.

How do anaesthetics work?

A medication used for anaesthesia is called an anaesthetic. Anaesthetics work by blocking the signals that pass along your nerves to your brain. When the anaesthetic wears off, you start to feel normal sensation again.

General anaesthesia always needs a specialist doctor, called an anaesthetist, to be present. However other forms of anaesthesia, such as nerve blocks and sedation, can be given by other specialist doctors in hospital, such as the initial treatment of some joint dislocations or bone fractures in the Emergency Department. General Practitioners often provide local anaesthesia for minor operations such as removing a cyst or a toenail operation.

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Types of anaesthesia

Local anaesthesia

A local anaesthetic numbs a small part of the body. It is used when the nerves can be easily reached by drops, sprays, ointments or injections. You stay conscious but free from feeling pain. Common examples of surgery under local anaesthetic are having teeth removed, operations for an ingrowing toenail, and some common operations on the eye.

Regional anaesthesia

This involves local anaesthetic being injected near to the nerves which supply a larger or deeper area of the body. The area of the body affected becomes numb. Anaesthetists often use an ultrasound machine or nerve stimulator to identify the exact position of the nerves.

The different types of regional anaesthesia include:

  • A spinal anaesthetic - a single injection in your back and into your spine, which makes you numb for about two hours. See also the separate leaflet called Spinal Anaesthetic.

  • An epidural anaesthetic - a needle is used to place a very fine tube (epidural catheter) in your back. 'Top-up' local anaesthetic is given for pain relief through the catheter, which can make the numbness last many hours or a few days. See also the separate leaflet called Epidural Pain Relief After Surgery.

  • Nerve block - an injection is placed near to a nerve or group of nerves - for example, in the arm or leg. This can allow you to have the operation without a general anaesthetic. Nerve blocks are also useful for pain control after the operation, as the area will stay numb for a number of hours.

Spinal or epidural anaesthesia can be used for operations on the lower body, such as caesarean section, bladder operations, or hip replacement. You stay conscious but free from pain.

Sedation anaesthesia

Sedation involves using small amounts of anaesthetic medicines to produce a 'sleep-like' state. It makes you physically and mentally relaxed, but not unconscious.

If you have sedation, you may remember little or nothing about the operation or medical procedure. However, sedation does not guarantee that you will have no memory of the operation. This can only be achieved by a general anaesthetic.

General anaesthesia

General anaesthesia is a state of controlled unconsciousness during which you feel nothing. You will have no memory of what happens while you are anaesthetised.

A general anaesthetic is essential for a very wide range of operations, especially major operations on the heart, lungs or abdomen, and most operations on the brain or the major arteries. It is also normally needed for keyhole (laparoscopic) operations on the abdomen.

General anaesthetics can be given in two different ways:

  • An injection of an anaesthetic medicine into a vein.

  • Breathing in an anaesthetic gas.

These medicines stop the brain from responding to sensory messages travelling from the nerves in the body. Unconsciousness caused by general anaesthesia is different from a natural sleep. You cannot be woken from an anaesthetic until the medicines are stopped and their effects wear off.

General anaesthesia is only given under the close supervision of a specialist doctor called an anaesthetist, who can consider the best way to give you an effective anaesthetic and also to keep you safe and well. Anaesthetists are supported in their work by a team of trained staff.

This team includes operating department practitioners (ODPs), theatre nurses and recovery room staff. While you are unconscious, the team in theatre looks after you with great care. Your anaesthetist stays near to you all the time.

How long does anaesthetic last?

How long an anaesthetic lasts depends on the type of the anaesthetic, and the exact anaesthetic drug given.

  • Local anaesthetic usually lasts for a few hours.

  • Regional anaesthetics vary:

    • Spinal anaesthetics generally last between one and three hours, depending on the medication used.

    • Epidural anaesthetics are given through a tiny tube ('catheter') in the back. The epidural will keep working as long as medicines are being given through the catheter. This can be done automatically using a pump, or manually with a 'top up' when the epidural feels like it is starting to wear off. Once the epidural is stopped, the effect wears off within a few hours. Epidural catheters might stay in for hours (such as in childbirth) or a few days (such as after major surgery).

    • Nerve blocks last different times depending on the type of block and medication used. A single nerve block injection can last from a few hours, up to 24 hours. It's also possible to put a tiny tube ('catheter') near to the nerves to give more anaesthetic medicine continuously, making the block last longer (usually up to five days).

  • Sedation mostly wears off after an hour or two, depending on the medication and how deep the sedation was. People usually feel well enough to go home after this. However, sedation takes up to 24 hours to wear off fully. After having sedation, you must be accompanied home by a responsible adult who can remain with you overnight. You must not drive, work, look after other people, operate machinery, cook, or make important decisions until the sedative drugs have completely worn off (24 hours afterwards).

  • General anaesthetics can last from a few minutes to several hours, depending on how long the procedure or operation is. Your anaesthetist will monitor you closely, and ensure it lasts as long as needed. Once the procedure has finished and the anaesthetic medicines have been stopped, you usually start to wake up quite quickly and will generally be awake, but feeling drowsy or groggy, within an hour or two. Within a few hours, you'll usually be safe to go home or be moved to a hospital ward (depending on the circumstances). It takes longer to recover fully, though. If going home, you must be accompanied by a responsible adult who can stay with you for 24 hours. You should not drive, work, look after other people, operate machinery, cook, or make important decisions for 24-48 hours after a general anaesthetic. Most people feel better within 48 hours, but it can take longer - days to weeks - to recover fully, especially if you've had a major operation.

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What are the side-effects and risks of anaesthetics?

Anaesthesia has made modern surgery possible. Sophisticated operations can be offered with a high degree of comfort and safety. But there are risks or possible side-effects caused by anaesthesia and anaesthetic medicines.

Common side-effects of anaesthetics

Feeling sick (nausea) and being sick (vomiting)

Anti-sickness medicines are routinely given with most anaesthetics to reduce the risk of this happening, and extra doses can be given to treat feeling sick or vomiting. See also the separate leaflet called Sickness after Anaesthetic.

Sore throat

For most general anaesthetics, the anaesthetist will place a tube in your airway to help you breathe. This can give you a sore throat. The discomfort or pain may last from a few hours to a few days. It is treated with pain-relieving medicines.

Dizziness and feeling faint

Anaesthetics can cause low blood pressure. Your anaesthetist will treat low blood pressure with medicines and fluid into your drip, both during your operation and in the recovery room. You will only go from the recovery room back to the ward when your blood pressure is stable.


You may shiver if you become cold during your operation. Care is taken to keep you warm and to warm you afterwards if you are cold. A hot-air blanket may be used. Shivering can also happen even when you are not cold, as a side-effect of anaesthetic medicines.


The potential causes of headache include the operation, dehydration, and feeling anxious. Most headaches get better within a few hours and can be treated with pain-relief medicines. Severe headaches can happen after a spinal or epidural anaesthetic. See also the separate leaflet called Headache after Anaesthetic.

Chest infection

A chest infection is more likely to happen after major surgery and after surgery in people who smoke. It is treated with antibiotics and physiotherapy. Occasionally severe chest infections develop which may need treatment in the intensive care unit and can be life-threatening.


This is a side-effect of opiate pain-relief medicines. It can also be caused by an allergy to anything you have been in contact with, including medicines, sterilising fluids, stitch material, latex and dressings. It can be treated with medicines to reduce itching.

Aches, pains and backache

During your operation you may lie in the same position on a firm operating table for a long time. You will be positioned with care; however, some people still feel uncomfortable afterwards. Muscle pains can also happen if you receive a medicine called suxamethonium. Your anaesthetist will tell you if you need this medicine.

Pain when medicines are injected

Some medicines used for general anaesthesia or for sedation given with regional anaesthesia cause pain when injected.

Bruising and soreness

This can happen around injection and drip sites. It may be caused by a vein leaking blood around the cannula or by an infection developing. It normally settles without treatment other than removing the cannula.

Confusion or memory loss

This is common among older people who have had a general anaesthetic. It may be due to an illness developing such as a chest or urine infection. There are other causes which the team looking after you will take care to treat. It usually recovers but this can take some days, weeks or even months.

Bladder problems

Difficulty passing urine, or leaking urine, can happen after an operation. If this happens, you may need to have a tube placed into your bladder (a urinary catheter) to drain the urine into a bag. Most bladder problems get better, so that your normal urinary habit returns before you leave hospital.

Uncommon risks of anaesthetics

Breathing difficulties

Some people wake up with slow or slightly difficult breathing after a general anaesthetic. If this happens to you, you will be cared for in the recovery room with your own recovery nurse until your breathing is better.

Damage to teeth, lips or tongue

Damage to teeth happens in 1 in 4,500 anaesthetics. Your anaesthetist will place a breathing tube in your throat at the beginning of the anaesthetic, and this is when the damage can happen. It is more likely if you have fragile teeth, a small mouth or a stiff neck. Minor bruising or small splits in the lips or tongue are common; however, these heal quickly.

Accidental awareness

Accidental awareness is becoming conscious during some part of a general anaesthetic. It happens because you are not receiving enough anaesthetic to keep you unconscious. The anaesthetist uses monitors during the anaesthetic which show how much anaesthetic is being given and how your body is responding to it. These should allow your anaesthetist to judge how much anaesthetic you need.

Accidental awareness is rare. It's debated as to exactly how often it occurs; depending on how it's measured, estimates are that between 1 in 20,000 to 1-2 in 1,000 people who have a general anaesthetic have some experience of awareness.

If you think you may have been conscious during your operation, you should tell any member of the team looking after you. Your anaesthetist will want to know so they can help you at this time and with any future anaesthetic you may have.

Damage to the eyes

It is possible that surgical drapes or other equipment can rub the clear surface of the eye (the cornea) and cause a graze. This is uncomfortable for a few days but with some eye-drop treatment it normally heals fully. Anaesthetists take care to prevent this. Small pieces of sticky tape are often used to keep the eyelids together, or ointment is used to protect the surface of the eye. Serious and permanent loss of vision can happen, but it is very rare.

Nerve damage

Nerve damage (paralysis or numbness) has a number of causes during local, regional or general anaesthetics. It varies with the type of anaesthetic you are having. Temporary nerve damage can be common with some types of anaesthetic, but full recovery often follows. Permanent nerve damage to nerves outside the spinal column is uncommon. See also the separate leaflet called Nerve Damage after Anaesthetic.

Existing medical conditions getting worse

Your anaesthetist will make sure that any medical condition you have is well treated before your surgery. If you have previously had a heart attack or a stroke, the risk that you will have another one is slightly increased during and after your operation. Other conditions such as diabetes, high blood pressure and asthma will be closely monitored and treated as necessary.

Rare side-effects of anaesthetics

Serious allergy to medicines

Allergic reactions can happen with almost any medicine. Your anaesthetist uses continuous monitoring which helps make sure that any reaction is noticed and treated before it becomes serious. Very rarely, people die of an allergic reaction during an anaesthetic. It is important to tell your anaesthetist about any allergies you know you have.

Damage to nerves in the spine

Permanent damage to the nerves in your spine is very rare after a general anaesthetic, a spinal anaesthetic or an epidural anaesthetic.

Equipment failure

Many types of equipment are used during an anaesthetic. Monitors are used which give immediate warning of problems, and anaesthetists have immediate access to back-up equipment. The chance of a serious event due to equipment failure is rare or very rare.


Deaths caused by anaesthesia are very rare. There are probably about five deaths for every million anaesthetics given in the UK. See also the separate leaflet called Death or Brain Damage from Anaesthesia.

Preparing for an operation

The time you have to prepare will vary depending on the reason for the operation. It's important to be as fit and well as possible before any operation using general anaesthesia. However, this isn't always possible. If your operation is an emergency, your doctors and nurses will give you good care in the condition you are in.

Medical problems

If you have a long-term condition, such as diabetes, asthma or bronchitis, heart problems or high blood pressure, you should make sure you are as well as possible before your operation. If you think you could make some improvement, you should see your doctor for an extra check-up.


If you smoke, you should consider giving up before your operation. Smoking increases the risk of problems during and after the operation. Your surgical wound will heal more slowly and be more likely to become infected if you smoke. If you plan to quit smoking, it is a good idea to see your doctor for help and advice to help you stop smoking.

Your weight

Many of the risks of having an operation are increased if you are very overweight. Your GP can give you advice about weight loss and put you in touch with an organisation that can help.


If you drink more alcohol than the recommended amount, you should cut down before an operation.

Fitness testing before an operation

Your surgeon may ask you to do a fitness test before you decide that you will have the operation. A fitness test gives information about how risky the operation is for you.

The pre-assessment clinic

Before having an operation, it's essential to know about your general health and to know what medicines you're taking. Some hospitals use a health questionnaire, or you may be invited to a pre-assessment clinic. If you are having an urgent operation, the health check will be done by your doctors and nurses on the ward.

If you're having a major operation then you may need to have some tests. These tests may include blood tests, a heart tracing (electrocardiogram, or ECG), an X-ray, or other tests. This is a good time to ask questions and talk about any worries that you may have.

In the few days before your operation


You should continue to take your medicines up to and including the day of the operation unless you are told not to. You should carefully follow any instructions you're given at the pre-assessment clinic.

Taking a shower

Some hospitals give patients a disinfecting shower gel to use for several days before the operation. It helps prevent serious infections such as MRSA. You should use this on your body and hair.

On the day of your operation

Nothing to eat or drink

The hospital should give you clear instructions about eating and drinking, which you should follow carefully. You may be given:

  • A time to stop eating, or drinking anything except water; and

  • A time to stop drinking water.

The operation will be cancelled or postponed if you haven't followed these instructions. The reason is that if there is any food or liquid in your stomach during your anaesthetic, it could come up into the back of your throat and cause choking, or serious damage to your lungs.

If you are asked to take your normal medicines, you can do so with a small sip of water at any time.

In the anaesthetic room

The anaesthetic room is next to the operating theatre. Many hospitals do not have anaesthetic rooms but you will then receive the same care in the operating theatre itself.

The anaesthetic machine delivers oxygen and anaesthetic gases in controlled amounts. This anaesthetic machine also has monitoring equipment, which includes:

  • Heart monitor: sticky patches will be placed on your chest which give a heart tracing on the screen.

  • Blood pressure: a cuff is placed around your arm, which is usually set to read your blood pressure every five minutes or less.

  • Oxygen levels: a peg with a red light inside it is placed on your finger or toe. This records your oxygen level continuously.

  • Other monitors may be used for complicated surgery.

Your anaesthetist will need to give you medicines into a vein. They will do this through a small plastic tube (cannula) placed in a vein on the back of your hand or in your arm.

Intravenous fluids

You need to receive fluid during most operations to prevent your body becoming very dry (dehydration). This fluid may be continued afterwards until the time that you can drink normally. If you need a blood transfusion then this will also be given through the 'drip'.

Choice of anaesthetic

Sometimes there is a choice about which kind of anaesthetic and pain control is best for you. Having talked about the benefits, risks and your preferences, you and your anaesthetist can decide together which anaesthetic you will have.


A 'pre-med' is a medicine which is sometimes given shortly before an operation. You may be offered medicines to help with anxiety, to prevent sickness or to treat pain. You can ask your anaesthetist about having a pre-med if you want one.

Pain-relieving medicines

These are given to reduce your body's reaction to the surgery, as well as to provide pain relief afterwards.

Muscle relaxants

These are needed for certain operations only. They relax the muscles completely and the anaesthetist uses a ventilator to do the breathing for you. At the end of the operation, you will not be woken up until the anaesthetist is sure the muscle relaxant has worn off.

Other medicines

  • Antibiotics to prevent infection.

  • Anti-sickness medicines.

  • Paracetamol to help with pain relief.

  • Medicines to treat low blood pressure.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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