This guide is written by the Royal College of Anaesthetists.
You are going to have a hip or knee replacement soon. You may have heard that there are several different types of anaesthetic:
- a general anaesthetic
- a spinal anaesthetic
- an epidural anaesthetic
- a nerve block (to help with pain afterwards)
- a combination of anaesthetics.
Your anaesthetist will explain which anaesthetic methods are suitable for you, and help you decide which you would prefer.
A general anaesthetic
A general anaesthetic produces a state of controlled unconsciousness during which you feel nothing.
You will receive:
- anaesthetic drugs (an injection or a gas to breathe)
- strong pain relief drugs (morphine or something similar)
- oxygen to breathe
- sometimes, a drug to relax your muscles.
You will need a breathing tube in your throat whilst you are anaesthetised to make sure that oxygen and anaesthetic gases can move easily into your lungs. If you have been given drugs that relax your muscles, you will not be able to breathe for yourself and a breathing machine (ventilator) will be used.
When the operation is finished the anaesthetic is stopped and you regain consciousness.
You will be unconscious during the operation.
A general anaesthetic alone does not provide pain relief after the operation. You will need strong pain relieving medicines afterwards which make some people feel quite unwell. Or you may wish to consider a nerve block with a general anaesthetic (see below).
Some of the risks and side effects of general anaesthetics are described later in this booklet. You can get more information about general anaesthetics from the leaflet‘Anaesthesia explained’ and other leaflets in the series.
A spinal anaesthetic
A measured dose of local anaesthetic is injected near to the nerves in your lower back.
- you go numb from the waist downwards
- you feel no pain, but you remain conscious
- if you prefer, you can also have drugs which make you feel sleepy and relaxed (sedation).
Advantages – compared to a general anaesthetic
- There is some evidence that less bleeding may occur during surgery which would reduce your risk of needing a blood transfusion.
- You remain in full control of your breathing. You breathe better in the first few hours after the operation.
- You do not need so much strong pain relieving medicine in the first few hours after the operation.
- You should have less sickness and drowsiness after the operation and may be able to eat and drink sooner.
Some of the risks and side effects of a spinal anaesthetic are described later in this booklet. You can get more information about spinal anaesthetics from the leaflet ‘Your spinal anaesthetic’ (see inside front cover of this leaflet).
An epidural anaesthetic
A small plastic tube (an epidural catheter) is passed through a needle into a place near to the nerves in your back. Through this tube, you receive a measured dose of local anaesthetic and pain relieving drugs. You will experience a reduction of all feeling in your lower body.
Although operations can be done with an epidural alone, it is more commonly used for:
- operations expected to be very long, say more than three hours
- operations expected to be particularly painful afterwards.
For these operations, it is often combined with a spinal or a general anaesthetic.
- It can be topped up with more local anaesthetic, and therefore its effects can be made to last longer than a spinal anaesthetic.
- It can be used to make you comfortable for several days after the operation.
- Not all epidurals are fully effective in relieving pain after the operation. If this happens you will receive additional pain relief.
Some of the risks and side effects of an epidural anaesthetic are described later in this booklet. You can get more information from the leaflet ‘Epidurals for pain relief after surgery’.
A nerve block
This is an injection of local anaesthetic near to the nerves which go to your leg. Part of your leg should be numb and pain-free for some hours afterwards. You may also not be able to move it properly during this time.
If you are having a general anaesthetic, this injection may be done before the anaesthetic starts, or it may be done when you are unconscious.
- You usually need a lighter general anaesthetic and you should be less sick and drowsy afterwards. This is because you should need less strong pain relieving medicines during and after the anaesthetic.
- You should be more comfortable for several hours after the operation.
A combination of anaesthetics
You can have a spinal or epidural anaesthetic and a general anaesthetic together.
- You gain the benefits of a spinal or epidural anaesthetic but you are unconscious during the operation
- The general anaesthetic will be ‘lighter’.
- Unpleasant after-effects of the general anaesthetic may be less.
You can have a nerve block with a general anaesthetic, or after a spinal anaesthetic.
- You should be more comfortable for some hours after the operation than with a general anaesthetic or spinal anaesthetic alone.
Before your operation
You will be asked some questions to check your health before your operation. This may be at a pre-assessment clinic, or it may be by filling in a questionnaire, by talking to the doctors on the ward or by talking to your anaesthetist.
You will be asked about:
- your general health and fitness
- any serious illnesses you have had
- previous anaesthetics and if there were any problems known to you
- whether you know of any family members who have had problems with anaesthetics
- medicines, pills, inhalers or homeopathic remedies that you use
- any allergies that you have
- whether you smoke
- whether you drink alcohol
- whether you have any loose, capped or crowned teeth.
The anaesthetist’s visit
Your anaesthetist will meet you before your operation and he/she will talk to you about which kind of anaesthetic is suitable for you. This is a good time to ask questions and tell the anaesthetist about any worries that you have. You may find it useful to write down any particular concerns before meeting your anaesthetist so that you don’t forget anything.
Delaying your operation
Your anaesthetist may suggest delaying your operation for a few weeks. This may be because he/she thinks that:
- your health could be improved to reduce the risks of the operation or the anaesthetic.
- you need some more tests.
It is possible that your anaesthetist will think there are very high risks. You may want time to think about whether to go ahead with the operation. These concerns will also be discussed with your surgeon.
“This is how we usually do it”
You may find that your anaesthetist and the team of staff looking after you have very regular experience of a certain type of anaesthetic and less experience of others. This would add to the advantages of that technique over others.
Your preferences are important. Nothing will happen to you until you understand and agree with what is planned for you. You have the right to refuse if you do not want the treatment suggested.
On the day of your operation
Nothing to eat or drink – fasting (‘nil by mouth’)
The nurses looking after you should give you clear instructions about fasting. It is important to follow these. If there is food or liquid in your stomach during your anaesthetic, it could come up into the back of your throat and damage your lungs.
If you are not having a general anaesthetic, you will still be asked to follow these instructions. This is because a general anaesthetic may be needed unexpectedly, and you need to be prepared.
Having a ‘premed’ (pre-medication)
This is the name for drugs which are given before some anaesthetics.
Some premeds prepare you for the anaesthetic (for example a drug to prevent sickness), others help you to relax. They may also make you more drowsy after the operation. If you want to go home on the same day, this may be delayed. If you think a premed would help you, please ask your anaesthetist.
Your usual medicines
It is important that you continue to take your usual medicines, including inhalers, unless your surgeon or anaesthetist has advised you not to.
Getting ready for theatre
- You will be given a hospital gown to put on.
- Jewellery should be removed or covered with tape to prevent damage to it or to your skin.
- You can wear your hearing aid, glasses and dentures until you are in the anaesthetic room. If you are not having a general anaesthetic, you can usually keep them on during the operation.
- If you are having a hip replacement you will need to take off your pants. If you are having a knee replacement you may be able to keep them on, or you may be given paper pants to wear.
In the anaesthetic room
This is the room next to the operating theatre. Several people will be there, including your anaesthetist and an anaesthetic assistant.
The anaesthetist will use equipment to measure:
- your heart rate – three sticky patches on your chest (electrocardiogram or ECG)
- your blood pressure – a cuff on your arm
- the oxygen level in your blood – a clip on your finger (pulse oximeter).
A needle is used to put a thin soft plastic tube (a cannula) into a vein in the back of your hand or arm. Drugs and fluids can be given through this cannula.
If needles worry you, please tell your anaesthetist. A needle cannot usually be avoided, but there are things he or she can do to help.
During the operation
All anaesthetics may cause changes in:
- your heart rate
- your blood pressure
- your breathing.
Changes may also occur due to loss of blood, the use of surgical cement and the use of a tourniquet on your leg (knee replacements only).
Your anaesthetist may intentionally adjust your blood pressure and breathing to control your response to surgery. General anaesthetic drugs are given continuously throughout surgery and are stopped when the operation ends. A spinal, epidural or nerve block injection will wear off some hours after the operation is finished.
An anaesthetist will stay with you for the whole operation and watch your condition very closely, adjusting the anaesthetic as required.
You may lose a significant amount of blood during and after the operation.
- A blood transfusion can be used to replace the blood you have lost.
- Usually this is blood from a volunteer who has given blood to help others (a blood donor).
- A blood transfusion will not be recommended unless you have a significantly low blood count.
- Please ask your surgeon or anaesthetist if you would like to know more about blood transfusion and any alternatives there may be.
- It may be possible to collect blood that is lost during the operation and afterwards from the drain that the surgeon places in your leg. This blood can be given back to you through your drip.
After the operation
You will be taken to the recovery room, which is near to the operating theatre.
- You will have your own nurse in the recovery room. You will not be left alone.
- There will be other patients in the same room.
- You may need to breathe oxygen through a light plastic mask.
- You will have a drip (a bag of sterile water with added salt or sugar which is attached to your cannula and drips slowly into a vein).
- Your blood pressure, heart rate and oxygen level will be measured.
- If you have pain or sickness, the nurse will treat it promptly.
When the recovery room staff are satisfied that you have recovered safely from your anaesthetic you will be taken back to the ward.
Good pain relief is important and some people need more pain relief medicines than others. Here are some ways of giving pain relief:
Patient controlled analgesia (PCA)
This is a method using a machine that allows you to control your pain relief yourself. Small doses are given into a vein for immediate effect.
These are given into a vein for immediate effect, or into your leg or buttock muscle. Strong pain relieving drugs such as morphine, pethidine and codeine may be given by injection.
Pills, tablets or liquids to swallow
These take at least half an hour to work and you need to be able to eat and drink and not feel sick for these drugs to work.
These waxy pellets are placed in your back passage (rectum). They are useful if you cannot swallow or might vomit.
Nerve blocks and epidurals
As already described, these can give effective pain relief for hours or days after the operation.
You can get more information about pain relief from:
- The nurses on the ward
- Your anaesthetist
- The pain-relief team – some hospitals have a team of nurses and doctors who specialise in the relief of pain after surgery. You may be able to contact this team for advice before you come into hospital. Leaflets may be available about pain relief methods.
- Manufacturers’ information leaflets for patients about any drug you are offered (your nurses should be able to give you these leaflets).
Side-effects, complications and risks
In modern anaesthesia serious problems are uncommon. Risk cannot be removed completely, but modern equipment, training and drugs have made anaesthesia a much safer procedure in recent years.
Anaesthetists take a lot of care to avoid all the risks given in this section. Your anaesthetist will be happy to give you more information about any of these risks and the precautions taken to avoid them. You can also find more information in the leaflet’Anaesthesia Explained’ and in other leaflets in the series.
Index of side effects and complications
People vary in how they interpret words and numbers. This scale is provided to help:
- If something is very common, this means that about one in 10 will experience it.
- Common means about one in 100.
- Uncommon means about one in 1000.
- Rare means about one in 10,000.
- Very rare means about one in 100,000.
Common and very common side effects
- Pain around injection sites and general aches and pains
- You may not be able to pass water (urine) or you may wet the bed. This is because you are lying down, you may have pain and you may have received strong pain relieving drugs. A soft plastic tube may be put in your bladder (a catheter) to drain away the urine for a day or two. This is more common after spinal or epidural anaesthetics.
Spinal or epidural anaesthetics
- You will not be able to move your legs properly for a while.
- If pain-relieving drugs are given in your spinal or epidural as well as local anaesthetic, you may feel itchy and/or sick.
- Sickness – treated with anti sickness drugs
- Sore throat or damage to lips or tongue – treated with pain relief drugs
- Drowsiness, headache, shivering, blurred vision – may be treated with fluids or drugs
- Difficult breathing at first – this usually improves rapidly
- Confusion and memory loss are common in older people, but are usually temporary.
Uncommon side effects and complications
- Heart attack or stroke
- Damage to teeth
- Chest infection
- Awareness (becoming conscious during a general anaesthetic)
Rare or very rare complications
- Serious allergic reactions to drugs
- Damage to nerves
- Damage to eyes
- Vomit getting into your lungs
Frequently asked questions
Q Should I take all my usual medicines or tablets right up to my operation?
Your surgeon and anaesthetist will tell you which drugs they would like you to take and which ones to stop. It helps if you bring all your medication with you so they know what you usually take.
Q Do other drugs affect the anaesthetic?
Most drugs that treat heart, circulation or breathing problems have some effect on the anaesthetic. Your anaesthetist will be familiar with all the drugs that you take and will adjust the anaesthetic accordingly.
Q How do you know how much anaesthetic each person needs?
The amount of anaesthetic needed for a spinal or general anaesthetic varies with your age, your weight and build and your general health. There is no easy formula! Anaesthetists use their judgment and experience. They stay with you all the time and they adjust the anaesthetic as needed.
Q Can I bring a relative or friend with me?
It may be possible to arrange this. If this would help you, please ask the nurses on the ward or your anaesthetist if a relative or friend could come into the anaesthetic room.
Q How long does it take to regain consciousness after a general anaesthetic?
You regain consciousness in 5 – 20 minutes. It may be longer before your memory fully returns.
Q Am I likely to get long-term backache if I have a spinal injection?
You may have a bruise at the site of the injection, but this soon passes. Backache due to arthritis is common in people having a hip or knee replacement. It is not made worse by having a spinal or epidural injection.
Questions you may like to ask your anaesthetist
- Who will give my anaesthetic?
- What type of anaesthetic do you recommend?
- Have you often used this type of anaesthetic?
- What are the risks of this type of anaesthetic?
- How will I feel afterwards?
To read more about you and your anaesthetic, please click here
Association of Anaesthetists of Great Britain and Ireland
21 Portland Place
London W1B 1PY
Phone: +44 207 631 1650
Fax: +44 207 631 4352
This organisation works to promote the development of anaesthesia and the welfare of anaesthetists and their patients in Great Britain and Ireland.
Royal College of Anaesthetists
35 Red Lion Square
London, WC1R 4SG
Phone: + 44 20 7092 1500
Fax: + 44 20 7092 1730
This organisation is responsible for standards in anaesthesia, critical care and pain management throughout the UK.
The European Society of Regional Anaesthesia and Pain Therapy
c/o Department of Anaesthetics
The Alexandra Hospital
Worcestershire B98 7UB
Phone/Fax: +44 1527 512047
This organisation works to further regional anaesthesia in Europe.
This web page includes text taken from the The Royal College of Anaesthetists' (RCoA) leaflet 'Anaesthetic Choices for Hip or Knee Replacement, May 2008' but the RCoA has not reviewed this as a whole. Please click here to view the original leaflet.