Anaesthesia explained

Published: 01/03/2021

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 still tap water, and
  • a time to stop drinking still tap water. Keep yourself well hydrated 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.

Usual medication

If you are asked to take your usual medications, it is important to take these with a small sip of water. If you feel unwell on the day of your operation you should phone the ward that is expecting you and ask their advice.

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 preoperative assessment and ask further questions about your health. They may listen to your chest and look in your mouth. You will be able to ask questions and discuss any concerns you may have.

Your anaesthetist may delegate some or all of these tasks to an Anaesthesia Associate.

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 will decide together which anaesthetic you will have if there are any choices to be made.

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

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 medication which is sometimes given shortly before an operation for a number of reasons. You may commonly be offered drugs to reduce acid in your stomach, to prevent sickness or to manage pain after the operation. Sometimes you may be offered medication to help you relax.

Can my operation be cancelled at the last minute?

Unfortunately, cancellations do happen at the last minute if time runs out in theatre or there is no bed available. Occasionally, your anaesthetist or surgeon may find something about your health which is not expected. They might recommend that your operation is delayed until the problem has been investigated, reviewed or treated. This will be discussed with you and your surgeon.

Getting ready for ‘theatre’  

Hospitals all vary slightly as to how and where patients get ready for the operating theatre.

Changing for theatre

You will be given a hospital gown to wear. You may like to wear your own dressing gown over this while you wait. Wear some slippers or shoes that are easy to take off when you arrive in the theatre.

You can usually wear a plain wedding band, which will be taped to keep it safely in place.

You will usually be given two identity bracelets to wear.

You can keep your underwear on as long as it does not get in the way of the operation. Ask your nurse if you are unsure.

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 clots can form in your legs when you are lying very still during the operation.

Most patients will need to wear surgical stockings. A member of staff will measure your legs and can help you put the stockings on as they are very tight.

Personal items 

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

Waiting to go to theatre

There may be some waiting around before you go to theatre. Staff will try to keep this time to a minimum but it is a good idea to bring something to do, such as a book or a tablet, or you can listen to music through headphones.

If the wait is likely to be longer than two hours, it should be possible for you to have some more water to drink. Ask your nurses for advice if you feel thirsty.

Going to theatre 

Most people walk to the operating theatre. If you are walking, you can wear your own dressing gown and slippers. If you cannot walk far, a wheelchair may be used. If you have had a pre-med that makes you sleepy, you will go on a trolley or bed.

The operating-theatre department 

The operating theatre department includes the anaesthetic room, theatres and a recovery room. It is usually brightly lit and may have no natural light. Air conditioning may make it feel cool. 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. They will also ask when you last ate or drank and if you have any allergies. These safety checks must be done several times before your actual operation to make sure that you receive the correct care.

In the anaesthetic room

Some hospitals do not have separate 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. In some hospitals, anaesthesia associates are part of the anaesthetic team. There may also be an anaesthetist or other healthcare professional in training and a nurse from the theatre team.

Before anything further happens the team will make another check of your name, hospital number, date of birth and what operation you are expecting, to make sure all the details agree with the planned operation.


The ODP or anaesthetic nurse will attach you to monitoring equipment, which allows the team to closely follow your wellbeing during your operation.

Heart monitor 

Sticky patches will be placed on your chest that give a heart tracing on the monitoring screen.

Sticky pads connect wires to the chest for monitoring the heart

Blood pressure

A cuff is placed around your arm, attached to a blood pressure monitor. The monitor 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 other places such as your ears or toes. This continuously measures your oxygen level.

Other monitors may be used for more complex 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 your blood stream. They will do this through a small plastic tube placed in the vein. This tube 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. If you
have any concerns about this, please talk to your anaesthetist.

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

Different sized 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. Occasionally other sites are used, such as the foot.

Intravenous fluids – ‘a drip’

You need to receive fluids during most operations to prevent dehydration. This may be
continued after surgery until the time that you can drink normally. Your anaesthetist can give
you sterile fluid through a drip into your cannula to keep the fluids in your body at the right
level. Any blood you need will also be given through the cannula.

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. Adults can ask their anaesthetist about it if they have particular worries about the cannula.

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.

Having a general anaesthetic

You now have a cannula in place and the monitoring equipment is attached. The anaesthetist will usually 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. After you are unconscious, your anaesthetist will insert the cannula.

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. To read more about the importance of managing your airway and breathing, please see our Your airway and breathing during anaesthesia leaflet.