Risks

Risks Explained

Anaesthetics are very safe. However, no medical intervention is without risk. In anaesthesia, perhaps more than in any other field of medicine, training and practice is centred on patient safety. The risk of serious complications from an anaesthetic for a healthy patient is minimal. For patients who are less healthy, surgery and anaesthesia may be associated with greater risks.

General Anaesthesia

Common minor complications that may occur after an anaesthetic include:

  • Sore or dry throat that usually settles within 24 hours.
  • Nausea that may be due to surgery or anaesthesia.
  • You may have a small bruise at the site of a cannula (drip).
  • You may feel light-headed or tired for some time after surgery and anaesthesia.


Other complications are uncommon (occurring less than 1 in 100 cases).

Serious complications are possible but usually uncommon. Complications are more common for patients who are ill before surgery. Anaesthetists are trained to treat complications if they occur.

  • Allergy to anaesthetic drugs is very uncommon and anaesthetists are trained to treat allergic reactions.
  • Feeling the operation (an ineffective anaesthetic, also known as ‘awareness’) is uncommon. Reports of awareness vary between 1 in 600 and 1 in 20,000. The most recent and largest-ever study reported that 1 in 20,000 patients reported awareness after general anaesthesia. If this were to happen in most circumstances, you would not feel any pain. During the anaesthetic, drugs may be used that stop your muscles moving so you would feel unable to move. This would be temporary and would stop at the end of the operation. You must let your Consultant Anaesthetist know if you think this has happened.
  • Severe heart or lung disease that exists before surgery may be made worse both by surgery and anaesthesia. In elderly patients, such conditions may be revealed by the stress of surgery and anaesthesia.


Any concerns you have regarding potential complications please discuss with your Consultant Anaesthetist before surgery.

‘Local’ & ‘Regional’ Anaesthesia

Local anaesthetic techniques are very safe, and complications are uncommon. The area numbed or anaesthetised by the nerve block will feel weak, and you may not be able to move it for many hours.


  • The most common problem with nerve blocks is occasionally they may not work fully. This occurs in about 1 in 100 spinal anaesthetics, 1 in 20 epidural anaesthetics, and 1 in 10 arm or leg nerve blocks. It is important you tell the anaesthetist if you think a local anaesthetic block is not working. If this happens, the Consultant Anaesthetist will ensure you are comfortable by other means.
  • Bruising after local anaesthetic blocks is usually minor.
  • Headaches affect up to 1 in 100 younger patients after spinal and epidural anaesthetics, and these can be severe. In middle-aged and older patients, this is less common.
  • Temporary areas of numbness or mild weakness after a nerve block occurs in about 1 in 50-100 cases (depending on the area blocked).
  • Permanent problems rarely occur. Permanent major problems (such as permanent areas of weakness, numbness, pain or paralysis) occur about:
  • 1 in 50,000 times after a spinal anaesthetic
  • 1 in 6,000-12,000 times after an epidural anaesthetic
  • <1 in 5,000 after an arm or leg nerve block


If you would like to discuss any of these risks further, please ask your Consultant Anaesthetist.