General anaesthetics are medications used to cause a loss of consciousness so you’re unaware of surgery.
Despite there being a number of theories about how general anaesthetics work, the precise mechanisms remain unknown.
However, it is known that all anaesthetics interrupt the passage of signals along the nerves. This means that any stimulation to the body doesn’t get processed or recognised by the brain.
How general anaesthetics are given
General anaesthetic will be given to you by an anaesthetist (a specially trained doctor). It will either be given as a:
liquid that’s injected into your veins through a cannula (a thin, plastic tube that feeds into a vein, usually on the back of your hand)
gas that you breathe in through a mask
Your anaesthetist will stay with you throughout the procedure. They will make sure you continue to receive the anaesthetic and you stay asleep, in a controlled state of unconsciousness.
After the procedure, the anaesthetist will turn off the anaesthetic and you will gradually wake up.
When general anaesthetics are used
General anaesthesia is essential for some surgical procedures where it may be safer or more comfortable for you to be unconscious. It’s usually used for long operations or those that may be very painful. Examples include surgery to remove the gallbladder, hernia repair, liposuction or a hysterectomy.
Before having an operation, you will meet your anaesthetist and plan your anaesthetic together.
Your anaesthetist will look at your medical history and will ask whether anyone in your family has had problems with anaesthesia. They will also ask about your general health and lifestyle, including whether you:
have any allergies
smoke or drink alcohol
are taking any other medication
Your anaesthetist will also be able to answer any questions you have. Let them know if you’re unsure about any part of the procedure or if you have any worries or concerns. You should be given clear instructions to follow before the operation, including whether you can eat anything in the hours leading up to it.
General anaesthetics have some common side effects. Your anaesthetist should discuss these with you before your surgery.
Most side effects occur immediately after your operation and don’t last long. Possible side effects are listed below.
Feeling sick and vomiting after surgery – about 33% of people feel sick after an operation. This usually occurs immediately, although some people may continue to feel sick for up to a day.
Shivering and feeling cold – about 25% of people experience this. Shivering may last for 20-30 minutes after your operation.
Confusion and memory loss – this is more common in elderly people and is usually temporary.
Chest infection – this can sometimes occur in people who have abdominal surgery. It will make you feel feverish (hot and cold) and cause breathing difficulties.
Bladder problems – men may have difficulty passing urine and women may leak urine. This is more common after a spinal or epidural anaesthetic.
Dizziness – you will be given fluids to treat this.
Bruising and soreness – this may develop in the area where you were injected or had a drip fitted. It usually heals without treatment.
Sore throat – during your operation, a tube may be inserted either into your mouth or down your throat to help you breathe. Afterwards, this causes a sore throat in about 40% of people.
Lip or dental damage – about 5% of people may have small cuts to their lips or tongue from the tube, and around 1 in 4,500 people may have damage to their teeth.
Complications and risks
A number of more serious complications are associated with general anaesthetics, but they are very rare (occurring in less than one case for every 10,000 anaesthetics given).
Possible complications include:
a serious allergic reaction to the anaesthetic (anaphylaxis)
an inherited reaction to the anaesthetic
death – this is very rare (there is approximately one death for every 100,000 general anaesthetics given)
Complications are more likely to occur if you:
are having major surgery or emergency surgery
have any other illnesses
Your anaesthetist will discuss the risks with you before your operation. You may be advised to stop smoking or lose weight, if doing so would reduce your risk of developing complications.
In most cases, the benefits of being pain-free during an operation outweigh the risks.
While it’s possible for a person under general anaesthetic to wake during surgery and experience pain, this is very rare. The chance of this happening has been greatly reduced by using monitors to measure the amount of anaesthetic being given.