Risk explained

About risk

Risk is a part of life. All medical treatments carry risks, and so do many things that we do in life – such as driving on the motorway, swimming in the sea, or even eating certain types of food.

The way you feel about a risk is very personal to you, and depends on your personality, your own experiences and often your family and background. You may be a 'risk taker', a 'risk avoider' , or somewhere in between. You may know someone who has had a risk happen to them, even though that is very unusual. Or you may have read in the newspapers about a risk and be especially worried about it.

Anaesthesia – a risky business?

Having an anaesthetic is often thought to be especially risky, even though the facts are that very few people having an anaesthetic these days come to serious harm because of the anaesthetic. The surgery itself carries risks, not just the anaesthetic.

Having an anaesthetic is certainly potentially dangerous, but it is made very much safer by anaesthetists’ training and equipment. Your anaesthetist stays beside you all the way through the anaesthetic and they can adjust the dose to keep you unconscious and safe. They are trained to watch you and all the monitors carefully and in what to do quickly if anything unplanned happens. They work with a trained assistant and have a range of equipment and medicines to bring you safely through your anaesthetic.

How is risk calculated?

Some of the information you are given about risks, including everything in this website, is based on information from studies or surveys. Other information you may be given will be based on the anaesthetist’s own judgement and experience. This may be because the exact risks are not known, as, in some cases, they have never been measured. Also, your anaesthetist needs to work out the risk for you based on your health, which may make risk higher or lower than the average.

For example, If you think about the risk of damage to teeth (quoted as happening in 1 in 4500 general anaesthetics). You may have a higher risk than that, if you have  teeth that are not in very good condition. Or you may have a lower risk than that, if you are not having the kind of anaesthetic that is most often linked to damaged teeth.

Balancing risks and benefits

There is always a balance between risks and benefits. Some operations do not have a guaranteed success rate. And all operations have some risks attached to the surgery itself. So, if you want to make an informed decision, you will need to put together information from your surgeon and your anaesthetist.

People vary in how they feel about the same risk. Also, it might change as you get older. Your anaesthetist will want to share information with you about the level of risk for you personally. They can also explain to you the different types of anaesthetic that you could have and what the advantages are of each option. After that, you can decide with your anaesthetist the ‘best way forward’ for you. 

You will want to consider all the risks and benefits that the operation will bring to your life to help you make a decision.

I really can’t decide – who can help me?

If you find it difficult to decide what to do – (and many people do) – these are some people who can help you.

  • Your GP or practice nurse if they know you well.
  • Your anaesthetist and surgeon. They will give you their expert opinion based on their experience of the procedure.
  • Other patients who have been through the treatment that is being suggested. This can be especially helpful, but is sometimes difficult to set up. If you are in hospital, your nurses on the ward may be able to find someone for you to talk to you. There are many patient forums on the internet but the quality of the information is very variable and may contain incorrect facts.

Can I do anything to reduce my own risk?

The answer to this is usually  – yes! All the information on this website, starting with  the You and Your Anaesthetic leaflet the Fitter Better Sooner toolkit, tells you if there is anything you can do to help yourself. This might start with giving up smoking or having your teeth checked over, trying to lose some weight or doing  some regular exercise to make you fitter before your operation.

How risk is presented

On this website and in our leaflets, we have linked numbers to words like in the scale below. For example in the sentence 'nerve damage is rare' – you know that it means that the risk of nerve damage in that circumstance is about 1 in 10,000. You will also find that more exact numbers are used in some places, to give you the best information available.

Numbers can be used in different ways to mean the same thing. Here is a guide to help:

If 100 people have an anaesthetic and 10 feel sick afterwards, the risk may be described as 10 in 100 OR 1 in 10.
This is also the same as 10% (or 10 per cent).

More examples:

1 person in 100

1 in 100


1 person in 1,000

1 in 1,000 


1 person in 10,000

1 in 10,000


50 people out of 10,000

50 in 10,000 OR 1 in 200



Pictures and diagrams are sometimes used to help you understand what is meant by these numbers. This may help you decide how you feel about the risk that has been explained to you.

The following diagram may also help you decide how you feel about risk:

Patient risk scale