Anaesthesia explained

Published: 02/08/2019

On the day of your operation

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. Please have a normal-size glass of water just before this time.

The reason is that if there is food or liquid in your stomach during your anaesthetic, it could come up into the back of your throat and then go into your lungs. This would cause choking, or serious damage to your lungs.

In an emergency, when people have not had time to stop eating and drinking, an anaesthetic can be given safely using a different technique.

Normal medicines 

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

If you feel unwell on the day of your operation 

You should phone the ward that is expecting you and ask for their advice. 


It is best to leave most jewellery at home.

Meeting your anaesthetist 

You will normally meet your anaesthetist on the ward before your operation. 

Your anaesthetist will look at the information from your health check or pre-assessment. They may listen to your chest and look in your mouth. They will ask you about any loose or crowned teeth. 

Choice of anaesthetic 

Sometimes there is a choice about which kind of anaesthetic and pain relief 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. 

Nothing will happen to you until you understand and agree with what has been planned. You can refuse the treatment, or ask for more information or more time to decide. 


A ‘pre-med’ is a drug which is sometimes given shortly before an operation. You may be offered drugs 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.

Will my operation be cancelled? 

Very occasionally, your anaesthetist may find something about your health which is not expected. They might recommend that your operation is delayed until the problem has been reviewed or treated. This will be discussed with your surgeon.

Getting ready for ‘theatre’  

Events will vary between hospitals.  

Washing and changing 

You will be able to use a shower if you want to. This will clean your skin and reduce the risk of infection. 

Make-up or body lotions are best avoided, as they prevent heart monitor pads and dressings from sticking properly. Please remove nail varnish and ask for advice about false nails.

Some types of false nail interfere with monitoring the oxygen level in your blood. This is because a finger clip is used which shines a light through your finger nail. 

You will be given a hospital gown to wear. You may like to wear your own dressing gown over this while you wait. 

You will be given an identity bracelet to wear. 

You can keep your pants on as long as they do not get in the way of the operation. Some hospitals provide paper pants.

Surgical stockings to prevent blood clots   

Your anaesthetist is jointly responsible, with the surgeon and the team in theatre, for treatment to reduce the risk of blood clots. These can form in your legs when you are lying very still during the operation. 

Most patients will need to wear surgical stockings. Your nurses will measure your legs for these and help you get them on. They are very tight.

Personal items 

You can normally wear glasses, hearing aids or dentures until the anaesthetic room. You may then need to remove them. The team will look after them carefully. 

Ideally you should remove jewellery and piercings. They may be damaged or get caught on things and injure you. If they cannot be removed, they will be covered with tape to try and prevent injury.

Waiting to go to theatre

There may be some waiting around before you go to theatre. Staff will try to keep this to a minimum. It is a good idea to bring something to do. 

If the wait is longer than two hours, it may be possible for you to have some more water to drink. Ask your nurses for advice on this.

Going to theatre 

Most people walk to the operating theatre. If you cannot walk far, a wheelchair may be used. If you have had a pre-med which makes you sleepy, you will go on a trolley or bed.

The operating-theatre department 

The operating-theatre department includes the theatres and a recovery room. It is usually brightly lit and often has no natural light. Air conditioning may make it feel quite cold. It is a good idea to wear a dressing gown or ask for a blanket. 

If you have walked to theatre, you will now be asked to lie on a theatre trolley. This is narrower than a bed and may feel quite firm to lie on. 


When you arrive in the department, staff will check your name, your identity band and what operation you are having. If relevant, they will ask you  if the operation is on the right or left side of your body. These are compulsory safety checks that make sure you have the correct care.

In the anaesthetic room

Many hospitals do not have anaesthetic rooms. If this is the case in your hospital, you will receive the care described here in the operating theatre itself.  

The anaesthetic room 

This room is next to the operating theatre.

Several people will be there, including your anaesthetist and an ODP or anaesthetic nurse. There may also be an anaesthetist in training, a nurse from the theatre team and other health professionals who are training.

An important piece of equipment is the anaesthetic machine. You can see it on the left of this photograph. It delivers oxygen and anaesthetic gases in controlled amounts. This anaesthetic machine has the monitoring equipment on the upper shelf, above the gas controllers.


The anaesthetist will attach you to monitoring equipment, which allows them to closely follow your wellbeing during your operation. 

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. All this information is passed to the screen so the anaesthetist can quickly see that you are responding well to the anaesthetic.

Setting up your cannula  

Your anaesthetist will need to give you drugs into a vein. They will do this through a small plastic tube placed in the vein. This is called a cannula. 

A needle is used to put the cannula into a vein on the back of your hand or in your arm. 

The anaesthetist will use a tourniquet (tight band) around the arm, to make the vein more obvious. Often the anaesthetic practitioner will hold or squeeze the arm instead of using a tourniquet.

Different size cannulas are available for different purposes. The anaesthetist will use the smallest one that meets your needs.

Sometimes, it can take more than one attempt to insert the cannula. You may be able to choose where your cannula is placed. Occasionally other sites are used, such as the foot.

Intravenous fluids – ‘a drip’

You need to receive fluid during most operations, to prevent dehydration. This fluid may be continued afterwards until the time that you can drink normally. Your anaesthetist can give you sterile water with added salt or sugar through a drip into your cannula to keep the right level of fluids in your body. Any blood you need will also be given through the drip.

Cannulas for children and those who find needles difficult 

Local anaesthetic cream can be used to reduce the sensation when the needle is inserted. The cream is used routinely for children, but adults may have to ask for it, and it may not always be available.

Having a general anaesthetic 

You now have a cannula in place and the monitoring equipment is attached. 

Many anaesthetists will ask you to breathe pure oxygen from a light plastic face mask before the anaesthetic begins. If you are worried about using a face mask, please tell your anaesthetist. 

Two ways of starting a general anaesthetic
  • Anaesthetic drugs are given through your cannula. This is the usual way of starting the anaesthetic if you are an adult or older child. Some people report a light-headed feeling first, and most people become unconscious within one minute. 
  • Or, you can breathe a mixture of anaesthetic gases and oxygen through the light plastic face mask. The gases smell quite strong, and it usually takes two or three minutes to become unconscious.
Looking after your breathing 

Your anaesthetist will choose a way of making sure that oxygen and gases can move in and out of your lungs easily. Usually this means a tube is placed in your airway. There are different types of tube for different circumstances.