Page last reviewed: 13/07/2011

Anaesthesia means "loss of sensation". Medications that cause anaesthesia are called anaesthetics. Anaesthetics are used for pain relief during tests or surgical operations so that you do not feel any of the following:

  • pain
  • touch
  • pressure
  • temperature

How do anaesthetics work?

Anaesthetics work by blocking the signals that pass along your nerves to your brain.

Your nerves are bundles of fibres that use chemical and electrical signals to pass information around your body. If you cut your finger, the pain signal travels from your finger to your brain through your nerves. When the signal reaches your brain, you realise that your finger hurts.

Anaesthetics stop the nerve signals reaching your brain, allowing procedures to be carried out without you feeling anything. When the anaesthetic wears off, the signals will work again and your sensation will come back.

Types of anaesthesia

There are several different types of anaesthesia. Most types do not make you unconscious, but they stop you feeling pain in a particular area of your body.

The different types of anaesthetic are described below.

  • Local anaesthetic - used for minor procedures and tests to numb the nerves in the area where the procedure is taking place. You will be conscious during the procedure but you do not feel any pain. 
  • Regional anaesthetic - used for larger or deeper operations where the nerves are harder to reach. Local anaesthetic is injected near the nerves in order to numb a larger area, but you remain conscious.
  • Epidural anaesthetic - a regional anaesthetic used to numb the lower half of your body, which is often used for childbirth.
  • Spinal anaesthesia - a regional anaesthetic that is used to numb your spinal nerves so that surgery can be carried out in this area.
  • General anaesthetic - used for bigger operations when you need to be unconscious. The anaesthetic stops your brain recognising any signals from your nerves, so you cannot feel anything. 
  • Sedation - for painful or unpleasant procedures that are otherwise minor. Sedation makes you feel sleepy and relaxes you both physically and mentally.   

Different types of anaesthetic can be used at the same time. For example:

  • A regional anaesthetic can be used with a general anaesthetic to relieve pain after an operation.
  • Sedation may be used with a regional anaesthetic to make you relaxed during the operation as well as free from pain. 

You may be given your anaesthetic in one of the following forms, depending on which kind you are having:

  • ointment, spray, or drops that are rubbed onto your skin
  • an injection into a vein
  • a gas that you breathe in


Anaesthetists are specialist doctors who are trained in anaesthesia. Before your procedure, they will discuss with you what anaesthetic methods are appropriate, along with any risks or side effects. If you have any queries about your anaesthetic is important that you raise them with your anaesthetist.

You anaesthetist will make sure that you are safe throughout the surgery, and that you wake up comfortably after the procedure. They may also help with any pain relief that you need after the procedure.

Side effects

Anaesthetics consist of a number of medications, which can cause side effects in some people. Your anaesthetist will let you know what side effects you may feel for your specific anaesthetic. 

Some of the more common side effects include:

  • feeling sick or vomiting - about one in three people may feel sick after an operation
  • dizziness and feeling faint
  • feeling cold and shivering for up to half an hour - this is possible after a general anaesthetic or during/after a regional anaesthetic
  • headache
  • itchiness
  • bruising and soreness

The side effects do not usually last for very long and if necessary they can be treated with further medication. Inform the healthcare professionals who are treating if you experience any of the above side effects, or if you are in any pain after your procedure.

Complications and risks

There are a number of more serious complications associated with anaesthesia but fortunately they are very rare (occurring in less than one case for every 10,000 anaesthetics given). Complications include:

  • permanent nerve damage (causing paralysis or numbness)
  • a serious allergic reaction to the anaesthetic (anaphylaxis)
  • death, which is extremely rare (there is approximately one death for every 100,000 general anaesthetics given)

Whether you are at any risk of these complications will depend on: 

  • your medical history - whether you have any other illness
  • personal factors - whether you smoke or are overweight, for example 
  • the type of surgery needed - whether it is planned or carried out in an emergency, or whether it is a major or minor procedure
  • the type of anaesthetic needed. General anaesthetics can have more side effects and complications than local anaesthetics.

Before your operation, your anaesthetist will explain your risk of developing possible complications or side effects. Usually, the benefit of being pain-free during the procedure will outweigh the risks, but it is important that you discuss any concerns you have with your anaesthetist.


Content provided by NHS Choices and adapted for Ireland by the Health A-Z.

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