13 January 2021

Section 6: general anaesthetic

What is a general anaesthetic?

A general anaesthetic is a mixture of drugs that induces a deep sleep. It causes a loss of sensation, and so it is used to keep you unconscious and pain-free during an operation. You will not have any awareness of what is happening when the surgery is being carried out, and you will not remember what has happened.

An anaesthetist is a doctor who is trained in anaesthesia. It is the anaesthetist who will administer your general anaesthetic. They will usually be assisted by a specially-trained healthcare practitioner.

It is recommended that you have a general anaesthetic, however it is your decision to go ahead with it or not.

Please read on to fully inform yourself about the risks and benefits of a general anaesthetic to help you to make an informed decision. If you have any further questions, please do not hesitate to ask your surgeon assistant.

What are the benefits of a general anaesthetic?

To go ahead with your operation, you need to be in a state where you do not move and your muscles are relaxed, enablng the surgeon to perform your operation safely. Giving a general anaesthetic is a safe way to achieve this.

Are there any alternatives to a general anaesthetic?

Certain operations can only be performed under a general anaesthetic, although some types may allow consideration of other forms of anaesthesia.

Other forms of anaesthesia include injections near the area of the surgery (local anaesthetic) or injections of local anaesthetic near major nerves or your spinal cord (regional, epidural or spinal anaesthetic). During an operation using a local anaesthetic, you will be awake or under sedation, although the area being operated on will have been numbed.

What happens before a general anaesthetic?

If you are female, you may be required to have a pregnancy test. If there is any chance you might be pregnant, please let your healthcare team know, as sometimes the test may not show up an early-stage pregnancy.

Please do not eat in the six hours prior to the operation. You may have small sips of water up to two hours prior. If you have diabetes, then please let us know, as you will need special advice according to your treatment regimen.

Prior to being given the anaesthetic, the healthcare team will attach some monitors to you which measure your blood pressure and the amount of oxygen in your blood. If you need oxygen, they will give it to you through a mask or small tube under your nostrils.

Some final checks will then be carried out by your anaesthetist and the healthcare team. You may be  asked some of the same questions again, but it is important to answer carefully as these checks are carried out for your own safety.

How is a general anaesthetic given?

For the majority of people, the anaesthetic is given through a drip - a small tube inserted into a vein. It will usually take about 30 seconds before it works and you are put to sleep. You may feel an ache as the injection goes in, but by the time you wake up any discomfort is usually gone.

For other people, it might be more appropriate to give the anaesthetic as a gas. The anaesthetic gas is given through a face mask which you will be required to breathe in. This also takes about 30 seconds to work before you are put to sleep.

You will be monitored closely by your anaesthetist during your operation, and kept asleep by either giving you more of the anaesthetic through your vein or by breathing the anaesthetic gas. You may also be given pain relief or anti-sickness medication.

When the operation is completed, the anaesthetic will wear off and you will wake up.

Is a general anaesthetic safe?

For most people, a general aesthetic is safe. The risk of death is higher in people who are in ill health or in emergency surgery, and is a result of a person’s body not being able to cope with the procedure.

Some tests will need to be carried out before your operation by your anaesthetist. These will determine how safe a general anaesthetic is for you, and show if the healthcare team might need to do anything differently for you to keep you safe. The tests may include the following:

  • Blood tests to check for anaemia (your body not producing enough healthy red blood cells), the balance of salts in your blood, the level of sugar in your blood, or how well your blood clots.
  • ECG (electrocardiogram) to record the electric activity of your heart. This test may show the cause of an irregular pulse or evidence of a previous heart attack.
  • Lung-function tests may need to be carried out if you have asthma, bronchitis, emphysema or unexplained shortness of breath.

Sometimes, you may be required to see your GP or another specialist before your operation, based on the results of the anaesthetist’s investigations. This might be to improve your medical condition before surgery. This happens most often in people who have high blood pressure, angina, asthma, diabetes or anaemia that is not well controlled.

How will my anaesthetist know that I am really asleep?

There is no monitor available that can assess whether or not you are fully asleep. A very small number of people (one in 20,000) report being aware of what is happening during their operation, when they should be asleep. Throughout your operation, the anaesthetist continuously monitors the amount of anaesthetic in your body to reduce this risk.

What can I do to make the operation a success?

Keeping warm

Around the time of the operation, it is important to keep yourself warm. When you are having the operation, your anaesthetist will take steps to ensure that you stay warm for its duration. It is important to bring extra clothing with you, such as a dressing gown, as the hospital may be colder than your home. If you become too cold, you will have a higher risk of developing complications such as an infection of the surgical site (wound) or heart problems. Please let the healthcare team know if you feel cold.

Lifestyle changes

Smoking can increase the risk of developing postoperative complications and so, if you are smoker, it would be helpful that you stop smoking several weeks or more prior to your operation. Stopping smoking may reduce your risk of complications and also improve your long-term health.

What complications can happen?

There are risks with every surgery, which may be higher or lower for you based on your own individual circumstances. Any numbers discussed with you that relate to risk are taken from studies of people undergoing a general anaesthetic. Your anaesthetist will try to reduce the risk of complications.

Minor complications (not disabling or life-threatening)

  • 1 in 4 risk of feeling sick/of being sick after the operation. In certain people and for certain operations the risk is higher, but can be managed by your anaesthetist or ward doctor following your operation. If you are prone to being sick, please let your anaesthetist know prior to your operation.
  • 1 in 6 risk of a sore throat, which resolves quickly.
  • 1 in 20 risk of a headache following the operations. This is not usually severe and will reduce in time. You can treat a headache with simple painkillers such as paracetamol.
  • 1 in 20 risk of muscle or back pain. This is caused by the positioning during the operation. If you are aware that certain positions may cause you problems, please let your anaesthetist know.
  • 1 in 100 risk of damage to your front teeth or crowns. Your anaesthetist will always need to look inside your mouth. If you have any dental issues such as loose teeth, crowns or bridges, please let your anaesthetist know.
  • You may have trouble passing urine and might require a catheter for a few days following your operation.

Generally, around 4 in 10 people report some problem following a general anaesthetic.

Serious Complications

  • 1 in 10,000 risk of a change or loss in hearing. In these cases, it will usually resolve with time.
  • Injury to the eye. There is a 1 in 20 risk of short-term blurred vision, a 1 in 1,000 risk of serious damage needing further treatment, and a 1 in 25,000 risk of loss of sight. For some operations, the risk is higher. Your anaesthetist will discuss these risks with you.
  • 1 in 1,000 risk of damage to the nerves. Mild damage to the ulnar nerve that runs just behind your elbow can occur. Damage to nerves is usually mild, although the damage may be permanent.
  • Myocardial infarction (heart attack). If you were fit before the operation, this is unusual. You are at a higher risk of a heart attack if you have heart disease, high blood pressure or diabetes, although it is still unusual in these groups.
  • Stroke (loss of brain function resulting from an interruption of the blood supply to your brain). Again, a stroke is unusual, although there is a higher risk if you have heart disease, high blood pressure or diabetes.
  • Chest infection and other respiratory problems. There is a 1 in 20 risk of a minor breathing problem after a general anaesthetic. There is a higher risk in people who are smokers or who have chest or lung disease. If you are having an operation on your chest or abdominal area, then this poses further risk.
  • Allergic responses. There is a 1 in 10,000 risk of a life-threatening allergic reaction to the medication used in the anaesthetic. Your anaesthetist is trained to detect and treat any reactions that could happen.

If there is anything you do not understand please ask your anaesthetist or medical team.

How soon will I recover?

Your judgement and reactions can be affected after having a general anaesthetic. For 24 hours following your general anaesthetic, you should refrain from driving and operating machinery (this includes cooking). Do not do any dangerous activities, sign legal documents or drink alcohol during this time. 

If you go home on the same day, you will need a responsible adult to be with you for at least 24 hours. They should accompany you home in a car or taxi, and you should ensure that you have access to a telephone in case of an emergency.

If you are in general good health, you are more likely to do well following a general anaesthetic.


A general anaesthetic is usually a safe and effective way for you to have your operation.

The majority of people undergoing an anaesthetic do not have any complications and are happy with their experience. However, complications can happen, and you do need to be aware of them so that you can make an informed decision regarding having an anaesthetic. Knowing about the complications will also allow early detection and treatment if they do arise.



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