Anaesthesia explained

Published: 02/08/2019

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 

The following index lists possible side effects and complications according to how likely they are to happen. It starts with ‘very common’ and ‘common’ side effects and finishes with ‘rare’ or ‘very rare’ complications.

RA = risk relevant to regional anaesthesia.
GA = risk relevant to general anaesthesia.

Very common and common risks

Feeling sick and vomiting (RA GA)

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 (GA)

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 (RA GA)

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. 

Shivering (RA GA)

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.

Headache (RA GA)

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 (RA GA)  

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.

Itch (RA GA)

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 (RA GA)

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 (RA GA)

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

Bruising and soreness (RA GA)

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 (GA)

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 (RA GA)

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 

Breathing difficulty (GA)

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 (GA)

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 (GA)

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.

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 (GA)

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 (RA GA)

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 (RA GA)

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 

Serious allergy to drugs (RA GA)

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 (RA GA)

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

Equipment failure (RA GA)

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.

Death (RA GA)

If you are a healthy patient having non-emergency surgery, death from anaesthesia is very rare. An exact figure is not known, but it is around one death per 100,000 general anaesthetics. 

You can find out more about anaesthesia and risk and browse our series of risk leaflets here