What are the benefits and risks?
Are there any side effects?

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Benefits and risks of having an anaesthetic

Anaesthesia has made modern surgery possible. Sophisticated operations can be offered with a high degree of comfort and safety. 

However, there are risks associated with having an anaesthetic. These may be weighed up against the likely benefits of the operation. 

Everyone varies in the risks they are willing to take. Your anaesthetist will describe the risk to you, but only you can decide how much the risk affects your plan to have the operation you would like.

Thinking about risk 

The risk to you as an individual depends on: 

  • Whether you have any other illness;
  • Personal factors such as whether you smoke or are overweight; and
  • Whether the operation is complicated, long, or done as an emergency.

To understand the risk fully you need to know:

  • How likely it is to happen;
  • How serious it could be; and
  • How it can be treated if it happens.

The anaesthetist can also advise you whether there are any anaesthetic techniques that will reduce those risks.

Side effects and complications

Anaesthetic risks can be described as side effects or complications. These words are somewhat interchangeable, but are generally used in different circumstances, as shown below.

Side effects are the effects of drugs or treatments which are unwanted, but are generally predictable and expected. For example, sickness is a side effect of a general anaesthetic, although steps are taken to prevent it.

Complications are unwanted and unexpected events due to a treatment. However, they are recognised as events that can happen. An example is a severe allergic reaction to a drug, or damage to your teeth when inserting a breathing tube. Anaesthetists are trained to prevent complications and to treat them if they happen.

Index of side effects and complications 

This index lists possible side effects and complications according to how likely they are to happen. 

This chart shows what is meant in this booklet when a risk is described in words.

Very common

1 in 10

Someone in your family


1 in 100

Someone in a street


1 in 1,000

Someone in a village


1 in 10,000

Someone in a small town

Very rare

1 in 100,000

Someone in a large town

For example, if something is ‘very common’ it means that about 1 in 10 people will experience it. It also means it will not happen to about 9 out of 10 people.

Click below to find out more about the differently occurring risks

For reference, RA stands for Regional Anaesthetic; GA stands for General Anaesthetic

Very common and Common risks (1 in 10 to 1 in 100 people)

Feeling sick and vomiting

Some operations, anaesthetics and pain-relieving drugs are more likely to cause sickness than others. Anti-sickness drugs are routinely given with most anaesthetics and extra doses can be given to treat feeling sick (nausea) or vomiting.


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 drugs. 


Dizziness and feeling faint

Anaesthetics can cause low blood pressure. Your anaesthetist will treat low blood pressure with drugs 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 get 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 drugs.



There are many causes of headache after an anaesthetic. These 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. If this happens to you, your nurses should ask the anaesthetist to come and see you. You may need other treatment to cure your headache.


Chest infection

A chest infection is more likely to happen after major surgery on the chest or abdomen, after emergency surgery and after surgery in people who smoke. It is treated with antibiotics and physiotherapy. In some circumstances, having an RA, rather than a GA, can reduce the risk of a chest infection. Occasionally severe chest infections develop which may need treatment in the intensive-care unit. These infections 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 drugs, sterilising fluids, stitch material, latex and dressings. It can be treated with drugs. 


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, but some people still feel uncomfortable afterwards. Muscle pains can also happen if you receive a drug called suxamethonium. Your anaesthetist will tell you if you need this drug.


Pain when drugs are injected

Some drugs 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 GA. It may be due to an illness developing such as 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 months. 


Bladder problems

Difficulty passing urine, or leaking urine, can happen after most kinds of moderate or major surgery. If this happens, the team looking after you will consider whether you need a urinary catheter (soft tube) placed in the bladder, which drains the urine into a bag. If the difficulty is expected to get better very soon, it is best to avoid putting in a catheter if possible, because urine infection is more likely if you have a catheter. 

Your nurses will make sure that you are clean and dry as soon as possible. Most bladder problems get better, so that your normal urinary habit returns before you leave hospital.

Uncommon risks (1 in 1,000 people)

Breathing difficulty

Some people wake up after a general anaesthetic with slow or slightly difficult breathing. 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 and 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, but heal quickly.



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 anaesthethic you need.

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 cornea (clear surface of the eye) 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.


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 or very rare complications (1 in 10,000 to 1 in 100,000 people)

Serious allergy to drugs

Allergic reactions can happen with almost any drug. 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 either a general anaesthetic, spinal or epidural anaesthetics.

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.