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Anaesthesia Explained

Many people will be anxious or concerned before coming to hospital for an operation. This leaflet explains the process of having an anaesthetic and tries to answer common questions along the way.  It gives you information about how you may receive anaesthesia and pain relief for your operation. The information in this leaflet is adapted from the information provided by the Royal College of Anaesthetists.


Giving your consent:

 In order for you to be able to consent for anaesthesia it is essential that you read this entire leaflet.  If you wish to have more information, the links for more resources are given at the end of the booklet or you can contact the Department of Anaesthesia.


What is Anaesthesia?

The word ‘anaesthesia’ means loss of sensation.

There are different types of anaesthesia, at the Walton Centre the majority of the operations are performed under General anaesthesia and some operations are performed under local anaesthesia.

General anaesthesia

General anaesthesia is a state of controlled unconsciousness during which you feel nothing. You will have no memory of what happens while you are anaesthetised. A general anaesthetic is essential for most of the Brain and Spine operations.

Anaesthetic drugs are injected into a vein, or anaesthetic gases are given for the patient to breathe. These drugs stop the brain from responding to sensory messages travelling from nerves in the body. Anaesthetic unconsciousness is different from a natural sleep. You cannot be woken from an anaesthetic until the drugs are stopped and their effects wear off.

Local anaesthesia

A local anaesthetic numbs a small part of the body. It is used when the nerves can be easily reached by drops, sprays, ointments or injections. You stay conscious, but free from pain. Common examples of surgery under local anaesthetic are having teeth removed.

What type of anaesthetic will I get?

 The type of anaesthetic you will receive depend on exactly what operation you are having. This leaflet does not replace individual discussions with your anaesthetist prior to surgery but provides general information.

Who will give the anaesthesia?

Your anaesthetic is administered by an anaesthetist. Anaesthetists are doctors who have had specialist training in anaesthesia. It takes at least seven years to train to be a consultant anaesthetist.

In the UK it is a requirement that a named consultant anaesthetist is involved in the care of every patient. This does not mean a consultant will give every anaesthetic. You can ask to talk to a consultant if you want to. You may be looked after by a specialist anaesthetist or a trainee anaesthetist. All trainee anaesthetists will be appropriately supervised and a consultant is always available if needed.

Your anaesthetist is responsible for:

  • Assessing whether you are fit enough to have the anaesthetic for your operation;
  • Talking to you about which type of anaesthetic might be best and getting your permission (consent) for it;
  • Giving the anaesthetic and organising pain control afterwards; and
  • Looking after you immediately after the operation in the recovery room and/or in an intensive care unit


Before you come into hospital

Here are some things that you can do to prepare yourself for your operation and reduce the likelihood of difficulties with the anaesthetic.

If you smoke you should try to give up for several weeks before the operation. The longer you can give up beforehand, the better. Smoking reduces the amount of oxygen in your blood and increases the risk of breathing problems during and after an operation. If you cannot stop smoking completely, cutting down will help.

If you are very overweight many of the risks of having an anaesthetic are increased. Reducing your weight will help to reduce these risks.

If you have loose or broken teeth or crowns that are not secure, you may want to visit your dentist for treatment before your operation. This is because the anaesthetist may need to put a tube in your throat to help you breathe, and if your teeth are not secure they may be damaged.

If you have a long-term medical problem such as diabetes, asthma or bronchitis, thyroid problems, heart problems or high blood pressure (hypertension), if your condition is not controlled, we may refer you back to your GP.

Health check before your general anaesthetic

Before your anaesthetic we need to know about your general health. At the pre-operative assessment clinic we will carry out a health check by asking you questions. This is performed by specialist nurses trained in pre-op assessment. You may also need to have some tests, such as an ECG, blood tests and other special tests if necessary to make sure you are fit enough to have a general anaesthetic.


On the day of Operation

Getting ready for hospital

Washing and changing: Before coming to hospital you should have a shower. 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.

Fasting before your operation

You will not be allowed to eat or drink for several hours before your operation. This is purely for safety reasons. It is important that your stomach is empty before you are anaesthetised, 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. As a general rule you should not eat food or sweets for six hours before anaesthesia. Clear fluids (diluted fruit squash, water) may be drunk until two hours before anaesthesia. Chewing gum and eating sweets are not allowed. Please follow instructions you are given prior to admission.

Normal medicines before your operation

You should continue to take your medicines up to and including the day of the operation unless you are told not to.

Please follow carefully the instructions you have been given in the pre-assessment clinic. Please look out for specific instructions if you take:

  • drugs to thin your blood (for example, warfarin, dabigatran, rivaroxaban, clopidogrel, aspirin);
  • drugs for diabetes;
  • all herbal remedies; and
  • some blood-pressure pills

Meeting the Anaesthetist

You will normally meet your anaesthetist on the ward before your operation. The anaesthetist will ask you questions and explain what happens to you during your time in theatre. The anaesthetist may also examine you. This is the best opportunity for you to ask any questions you may have. Please make sure you raise any concerns you have about anaesthesia at this time. It may be useful to make a list of questions beforehand.

You and your anaesthetist can work together to make your experience safe and as comfortable as possible.


Please let the anaesthetist know about any dental problems (i.e. loose teeth and the presence of caps, crowns or dentures - even if in good condition) when you meet. While every effort is made to protect all teeth there is an increased risk of damage to damaged teeth, caps and crowns, especially at the front of the mouth. The overall risk of damage is very small indeed. If you have false teeth you will usually be asked to remove them before your anaesthetic. This is for reasons of safety. This can be done in the operating theatre if you wish. Your dentures will be returned to you as soon as you wake up after your operation.


You may be given drugs before surgery (a ‘pre-med’). This most frequently includes a pain-killer, or a drug to reduce sickness. Sometimes it also includes a drug to reduce Patient anxiety. If you would like something to relax you before your operation please discuss it with your anaesthetist at your preoperative visit.

Getting ready 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. You will be given an identity bracelet to wear. Most patients will need to wear surgical stockings to prevent blood clots. Your nurses will measure your legs for these and help you get them on.

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.

Going to theatre

Most people walk to the operating theatre. If you cannot walk far, a wheelchair, trolley or a bed may be used to transport you to theatre.


In the operation theatre

In the operating department:

At the Walton Centre theatre complex you will come to the theatre reception first where you will be asked to confirm who you are and what operation you are having. These careful checks ensure the right person arrives for the right operation. The theatre staffs wears ‘Burgundy’ theatre suits and wear paper hats, they all look the same, however you may recognise your surgeon and the anaesthetist.

In the anaesthetic room:

In the anaesthetic room you will be asked some questions again, to make sure the right person has arrived and that everyone understands precisely what surgery is planned. Although repetitive, this ‘check-list’ system is carried out to protect you, as it improves safety. We use the World Health Organization approved safety checklist for this purpose, as recommended throughout the NHS.

If you are having a general anaesthetic, you will probably now need to remove your glasses, hearing aids and dentures to keep them safe. If you would prefer to leave your dentures in place, ask your anaesthetist if this would be alright.

To monitor you during your operation, your anaesthetist will attach you to machines

  • Three small sticky patches will be placed on your chest (electrocardiogram or ECG) to monitor your heart.
  • A blood-pressure cuff will be placed on your arm which will inflate periodically to check your blood pressure.
  • A clip will be placed on your finger (pulse oximeter) to monitor the oxygen level in your blood.

Starting the anaesthetic (induction)

To send you off to sleep your anaesthetist will inject anaesthetic drugs into your vein. A needle will be used to put a thin plastic tube (a ‘cannula’) into your vein in the back of your hand or forearm. This is then covered with a sterile dressing to stop it slipping out. The anaesthetist will give you anaesthetic drugs through this cannula. This is called an induction to anaesthesia. Induction happens very quickly, and you will become unconscious (asleep) within a minute.

Following the induction you will be given:

Anaesthetic drugs or Anaesthetic gases to keep you asleep during the operation

Pain relieving drugs to keep you pain-free during and after your operation

Muscle relaxants to relax or temporarily paralyse the muscles of your body to help with the surgery (if required). If this is necessary, the anaesthetist will have to control your breathing

during this time. This is done by inserting a plastic tube into your windpipe while you are asleep. The tube is then attached to a ventilator that is used to breathe for you during the operation.

Antibiotics to guard against infection.

Anti-sickness drugs to stop you feeling sick.

The anaesthetist stays with you throughout your operation and keeps you safe. The anaesthetist pays attention to you at all times and fine-tunes the anaesthetic carefully in response to the surgery and your responses to it. At the end of surgery the anaesthetist ensures you wake up safely. They will be checking your body functions by watching the monitors, maintaining the appropriate level of anaesthesia and giving you any fluids or drugs that you need.

Waking up from a general anaesthetic

At the end of the operation, your anaesthetist will stop giving anaesthetic drugs and/or gases and you will wake up gradually. If muscle relaxants have been used, you will be given a drug that reverses their effect. For all but very major operation you will be breathing normally soon after the operation is over.

Other care you will receive during anaesthesia

Your anaesthetist shares responsibility with the surgeon and the theatre team for your overall wellbeing in the operating theatre.

Keeping you warm

The team will take care to keep you as warm as possible. They will measure your temperature during the operation, and warming blankets are used whenever necessary.

Protecting pressure points

Your anaesthetist will also make sure that you are positioned as comfortably as possible. Bony parts such as your heels and elbows will be cushioned.

Preventing blood clots

As well as surgical stockings, the theatre team may also use wraps around your calves or feet which inflate every now and then to move the blood around in your legs.

Blood transfusions

During most operations, you will lose some blood. If necessary, your anaesthetist will make up for this blood loss by giving you other types of fluid into a vein through a drip. If you lose a lot of blood, your anaesthetist will consider whether you need to have this replaced with donated blood (a blood transfusion). If your anaesthetist expects you to need a blood transfusion, they will discuss this with you beforehand, but there is a chance you might need blood unexpectedly. If it happens then the anaesthetist will discuss this with you after the operation. You will receive a leaflet and will no longer be able to donate blood in the future.

You have the right to refuse a blood transfusion, but you must make this clear to your surgeon before the operation. You may be asked to sign a document which confirms that you don’t want a blood transfusion. This will give us enough time to discuss the alternative options if you do need a transfusion, as some of them require preparation in advance.


After the operation

When your anaesthetist is sure that you are recovering normally, you will be taken to the recovery room. A designated recovery nurse will be with you at all times and will continue to monitor your blood pressure, oxygen levels and pulse rate. You will be given oxygen through a lightweight clear-plastic mask, which covers your mouth and nose. Breathing oxygen keeps up the levels of oxygen in your blood while the anaesthetic wears off.

The staff will remove your mask as soon as the oxygen in your blood stays at the right level without you having to breathe in extra oxygen.

You may temporarily need a urinary catheter. This is a thin soft tube put into your bladder while you are asleep, to drain the urine during and after the surgical procedure.

Returning to the ward

The recovery staff must be totally satisfied that you have safely recovered from your anaesthetic, you are comfortable, and all your observations (such as blood pressure and pulse) are stable, before you are taken back to the ward.

The type of operation you have had will affect how long it will be before you can drink or eat. After minor surgery, this may be as soon as you feel ready. Even after quite major surgery you may feel like sitting up and having something to eat or drink within an hour of regaining consciousness.

High-dependency unit (HDU) or intensive care unit (ICU)

After some major operations, you may need care in the HDU or ICU. If this is planned, it will be discussed with you beforehand



Pain relief

Good pain relief after your operation is important. As well as making you comfortable, it helps you get better more quickly.  If you have good pain relief, you will be able to breathe deeply and cough, at least gently (which will help make sure you do not develop a chest infection after your operation); and move about freely. Exactly how much and how soon you will move around the bed, or get out of bed, will depend on the operation you have had. Early movement helps prevent blood clots in your legs (deep-vein thrombosis or DVT). Getting out of bed helps you to expand your lungs and to avoid a chest infection. It also helps prevent stiff joints, an aching back and pressure sores where you have been lying.

Planning your pain relief

  • Your anaesthetist will talk with you before your operation about pain relief afterwards. You can discuss any preferences you have, and decide together what pain relief you will have. They will prescribe some pain relief, and more will be available if you need it.
  • The amount of pain relief you need depends on the operation you are having.
  • Some people need more pain relief than others.
  • Pain relief can be increased, given more often, or given in different combinations.
  • Most pain-relief treatments also have side effects. Your doctors will need to take these into consideration as they advise you on which type of pain relief is best for you.
  • Despite the use of all the pain relief therapies explained, sometimes it is not possible to eliminate all post operative discomfort related to surgery.
  • Occasionally, pain is a warning sign that all is not well, so you should tell your nurses about it.

Ways of taking pain relief

  • Your anaesthetist will be able to talk with you about which types of pain relief are appropriate for you.
  • Tablets or liquids to swallow: These are used for all types of pain. They take 30 minutes to work and are best taken regularly. You need to be able to eat and drink without feeling sick for these drugs to work.
  • Injections into a muscle: These are not needed very often, but may be prescribed as an extra form of pain relief if you unexpectedly have a lot of pain. They may be given into your leg or buttock muscle and take 10 to 15 minutes to work.
  • Intravenous pain relief (into a vein): During your anaesthetic and in the recovery room your anaesthetist and nurses may give you drugs into your cannula. This means they work more quickly than if the same drugs are given as a tablet or injection into a muscle.

Pain relief drugs

Two basic types of pain relief drug are given commonly.

  • Paracetamol
  • Anti-inflammatory medicines (Ibuprofen or similar drugs).

Each of these medicines can be given in some of the ways listed – as a tablet or liquid to swallow, by an injection into a muscle, or into a vein. They can be used together as they belong to different chemical groups.

Opiate pain relief medicines

These drugs are used after operations that are expected to cause considerable pain.

Morphine, diamorphine, pethidine, codeine, tramadol and oxycodone are all opiate pain-relief medicines. They may be given as a tablet or liquid to swallow, as an injection into a muscle, or intravenously into your cannula.

Side effects are common with these drugs. These include feeling sick, vomiting, itching, drowsiness and, if used over a few days, constipation. Larger doses can cause very slow breathing and low blood pressure. The nursing staff will watch you closely for all of these side effects. If they happen, other treatments will be given to keep you safe.

Your reaction to opiates will affect you considerably. Anti-sickness drugs will be given as well. One in three people find opiates unpleasant, but they are the most effective pain-relief medicines in many circumstances.


Other ways of giving pain relief- Patient controlled analgesia (PCA)

This is a system which allows you to control your own pain relief. Opiate drugs are put into a pump which is connected to your drip. The pump has a handset with a control button which you will be shown how to use. When you press the button, a small dose of the opiate drug goes straight into your drip.

Using a PCA allows you to help yourself to a small dose of pain relief very frequently. The anaesthetist sets the dose and also a minimum time limit between doses (usually five minutes). After that time has passed, you can decide whether you want another dose. The drug goes straight into a vein, and so works very quickly. You can continue to press the button at five minute intervals until your pain is reduced to a suitable level. You can then have further doses to top up your pain relief as you need them, and keep yourself comfortable.

Your nurses watch you carefully while you are using a PCA, to make sure that you are reacting safely to the pain-relief medicine. There is evidence showing that patients benefit from being in control of their own pain relief. This type of pain relief is at least as safe, or safer, than other ways of giving opiate pain relief.


Pain relief at home

Your anaesthetist or doctors on the ward (or both) will make a plan for your pain relief at home.

  • You may be asked about pain-relief drugs that you already have at home, such as paracetamol. It is a good idea to stock up on pain-relief tablets before you come into hospital. Staff at the pre-assessment clinic will be able to advise you about which pain- relief drugs may be useful.
  • If appropriate, you may be given a supply of pain- relief drugs to take home with you. You may be advised to take several different types of pain relief. It is important that you understand how to use the different drugs and that you are aware of possible side effects. This will be explained to you. It is helpful if a relative or friend listens when this information is given, to help you remember what to do. Ideally you will receive written information as well.


Going home and getting back to normal

You will be allowed to leave hospital when you are safe and well. As anaesthetic drugs disappear rapidly from your body, these are likely to have little effect on your recovery.

However you are advised to take things easy for the first 24 hours after an anaesthetic and should be accompanied by a responsible adult during this time. You should not return to work, operate machinery or drink alcohol, for 24 hours after an anaesthetic. You should not make important decisions or sign legal documents during this period. You must not drive a car for a minimum of 36 hours after an anaesthetic. Your insurance will not be valid if you do: as insurers vary in their rules if you need to drive please check with your own insurer.

It may take you considerably longer to recover from surgery itself. Your recovery will be helped by getting the right balance between rest and activity. Taking painkillers you have been prescribed will assist you to do this.

How you feel afterwards depends mainly on the operation you have had, and on the pain-relief medicine that you need to treat any pain that you have.  You may feel tired or even exhausted for some days after the operation. After major surgery this can last weeks or months. This is very unlikely to be caused by the anaesthetic.

Causes of tiredness after surgery include:

  • worry before the operation
  • poor sleep patterns
  • pain
  • blood loss causing anaemia
  • the condition that needed the surgery and
  • Poor eating and drinking.

These will gradually improve as you leave hospital and you are healing.


Who can give me advice when I am at home?

Before you leave the ward, you should make sure you know how and who to contact if you develop significant pain or other problems at home. You may get this information from:

  • The nurse who arranges your discharge from hospital
  • The doctors on the ward
  • In case of emergency you may consider going to your nearest A&E


Benefits and risks of having an anaesthetic

Anaesthesia has made modern surgery possible. Sophisticated operations can be offered with a high degree of comfort and safety. However, there are risks associated with having an anaesthetic. These may be weighed up against the likely benefits of the operation. Everyone varies in the risks they are willing to take. Your anaesthetist will describe the risk to you, but only you can decide how much the risk affects your plan to have the operation you would like.

Thinking about risk

The risk to you as an individual depends on:

  • Whether you have any other illness;
  • Personal factors such as whether you smoke or are overweight; and
  • Whether the operation is complicated, long, or done as an emergency.

To understand the risk fully you need to know:

  • How likely it is to happen;
  • How serious it could be; and
  • How it can be treated if it happens.

The anaesthetist can also advise you whether there are any anaesthetic techniques that will reduce those risks.

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

This index lists possible side effects and complications according to how likely they are to happen. For example, if something is ‘very common’ it means that about 1 in 10 people will experience it. It also means it will not happen to about 9 out of 10 people.


Very common and common side effects and complications (1 in 10 to 1 in 100)

  • Feeling sick and vomiting after surgery – This can be reduced by using anti-vomiting drugs (anti-emetics) during and after surgery, but it may last from a few hours to several days.
  • Sore throat – If you have had a tube in your airway to help you breathe, it may give you a sore throat. The discomfort or pain lasts from a few hours to a few days.
  • Dizziness and feeling faint – Your anaesthetic you have had may lower your blood pressure and make you feel faint. This may also be caused by dehydration (when you have not been able to drink enough fluids). Fluids or drugs (or both) will be given into your drip to treat this.
  • Shivering – Care is taken to keep you warm during your operation and to warm you afterwards. We may use a hot-air blanket may to do this. However, shivering can happen even when you are not cold, due to the effects of anaesthetic drugs.
  • Headache – There are many causes of headaches, including the anaesthetic, the operation, dehydration and feeling anxious. Most headaches get better within a few hours and can be treated with pain-relieving medicines.
  • Aches, pains and backache – This may be from lying still for a long time or from the operation itself.
  • Bruising and soreness – This may develop around injection and drip sites, as well as the area that has been operated on. It normally settles without treatment.
  • Confusion or memory loss – This is more likely in older people who have had an operation under general anaesthetic, or if you already have problems with your memory. It is usually temporary, but may sometimes be permanent and you may not be able to remember certain memories from just before your operation.
  • Chest infection – A chest infection is more likely to happen if you smoke, and may lead to breathing difficulties. It is very important to give up smoking for as long as possible before your anaesthetic, and to give up permanently for your future health.
  • Bladder problems – After certain types of operation men may find it difficult to pass urine, and women can tend to leak. To prevent problems, you may have a urinary catheter inserted during the procedure especially for major surgeries.


Uncommon side effects and complications (1 in 1000)

  • Breathing difficulties – Some pain-relieving drugs can cause slow breathing or drowsiness after the surgery. If muscle relaxants are still having an effect (as they have not been fully reversed), they can make your breathing muscles weak. These effects can be treated with other drugs.
  • Damage to teeth, lips or tongue during a general anaesthetic – Damage to your lips and tongue happens occasionally, but is not common. Damage to your teeth is also uncommon, but may happen if your anaesthetist needs to place a breathing tube in your windpipe. It is more likely if you have weak teeth, a small mouth, a stiff neck or a small jaw.
  • An existing medical condition getting worse – Your anaesthetist needs to be assured that you are as fit as possible before your surgery. That is why, if you have any existing medical condition (coronary heart disease, high blood pressure, diabetes, asthma, etc.) you will have to be checked by your GP and in the Pre-operative Assessment clinic to make sure that your condition is under the best possible control. If not, it has to be treated and brought up to this level before your surgery. However, even then, if you have had a heart attack or stroke, it is possible that it may happen again – as it might do even without the surgery.


Rare or very rare complications (1 in 10,000 to 1 in 100,000)

  • Damage to your eyes – Anaesthetists takes great care to protect your eyes from accidental pressure or dryness. Serious and permanent loss of vision can happen, but it is very rare.
  • Serious allergy to drugs – Allergic reactions will be noticed and treated very quickly. Before the operation, your anaesthetist will need to know about any allergies you or your family have.
  • Nerve damage – Most nerve damage is temporary, but in some cases damage is permanent.
  • Death – Deaths caused by anaesthesia are very rare. There are probably about five deaths for every million anaesthetics given in the UK.
  • Equipment failure – Vital equipment that could fail includes the anaesthetic gas supply or the ventilator. Monitors give an instant warning of problems and anaesthetists have immediate access to back-up equipment.
  • Awareness – Awareness is becoming conscious during some part of an operation under general anaesthetic. This is very rare.



  • Last Updated:
    01 December 2022
  • Review Date:
    01 December 2024
  • Author:
    Rajesha Srinivasaiah
  • Summary:

    This leaflet explains the process of having an anaesthetic and tries to answer common questions along the way.  It gives you information about how you may receive anaesthesia and pain relief for your operation.

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