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Anaesthesia means "loss of sensation". Medications that cause anaesthesia are called anaesthetics.

Anaesthetics are used during tests and surgical operations to numb sensation in certain areas of the body or induce sleep.

This prevents pain and discomfort, and enables a wide range of medical procedures to be carried out.

Local anaesthetics and general anaesthetics are two commonly used types of anaesthetics.

A local anaesthetic is often used during minor procedures where a small area of the body is numbed and you remain fully conscious. A general anaesthetic is often used for more serious operations where you're totally unconscious and unaware of the procedure.

How anaesthetics work

Anaesthetics work by stopping the nerve signals that keep you awake and aware from reaching your brain.

During this state of induced sleep, procedures can be carried out without you feeling anything.

After the anaesthetic has worn off, the nerve signals will be able to reach your brain, and consciousness and feeling will return.

Types of anaesthesia

As well as local and general anaesthetic, there are a number of other types of anaesthesia.

Unlike general anaesthetic, these don't make you unconscious; they stop you feeling pain in a particular area of your body.

The different types of anaesthetic are described below.

  • regional anaesthetic – this is a local anaesthetic given to a specific region of your body, giving numbness or pain relief for deeper operations where more extensive numbness is needed
  • epidural anaesthesia – a type of regional anaesthetic usually used to numb the lower half of the body; for example, as pain relief during labour and childbirth
  • spinal anaesthetic – a type of regional anaesthetic used to give total numbness lasting about three hours to the lower parts of the body so surgery can be safely carried out in this area
  • sedation – medication that makes you feel sleepy and relaxes you both physically and mentally; it's sometimes used to keep you calm during minor, painful or unpleasant procedures

Different types of anaesthesia can be used in combination. For example, a regional anaesthetic can be used with a general anaesthetic to relieve pain after an operation.

A sedative is also sometimes used with a regional anaesthetic to help you feel relaxed and calm during an operation, as well as pain-free.

How anaesthetics are given

An anaesthetic can be given in a number of ways:

  • as an ointment, spray or drops
  • as an injection into a vein
  • as a gas you breathe in


Anaesthetists are doctors who have received specialist training in anaesthesia. They'll give you your anaesthetic and be responsible for your safety and wellbeing during your procedure.

Before the procedure, your anaesthetist will discuss a number of things with you, including:

  • the types of anaesthetic appropriate for the procedure you're having
  • any risks or side effects associated with different types of anaesthetic

They'll plan your anaesthetic and pain control with you, taking into account any preferences you have for a particular type of anaesthetic. You should ask your anaesthetist to clarify anything you're unsure about.

Your anaesthetist will carefully monitor you throughout your operation and make sure you wake up comfortably afterwards. They may also help with any pain relief you might need after the procedure.

Side effects of anaesthesia

Anaesthetics consist of a number of medications that can cause side effects in some people. Your anaesthetist will tell you about any side effects you may experience after having a specific type of anaesthetic, and measures that will be taken to reduce these.

Some common side effects that can occur after having a general anaesthetic and some regional anaesthetics include:

  • feeling sick or vomiting
  • dizziness and feeling faint
  • feeling cold or shivering
  • headache
  • itchiness
  • bruising and soreness
  • difficulty passing urine
  • aches and pains

The side effects of anaesthetic don't usually last very long and, if necessary, some of them can be treated.

Tell the healthcare professionals treating you if you experience any of the above side effects or if you're in pain after your procedure.

Risks and complications of anaesthesia

In recent years, having anaesthesia has become very safe. Advances in equipment, medication and training mean serious problems are rare.

However, as with any type of surgery or medical procedure, there's a potential risk of complications.

The benefits and risks of surgery and anaesthesia will be carefully weighed up and explained to you before you have any operation.

Very rare possible complications include:

  • permanent nerve damage – this can cause numbness or paralysis (inability to move a part of the body), although this may be a result of the surgery itself; peripheral nerve damage occurs in less than 1 in 1,000 anaesthetics (the peripheral nerves run between the spinal cord and the rest of the body)
  • an allergic reaction to an anaesthetic medication (anaphylaxis) – although this can be severe, appropriate treatment is on hand to enable the best chance of dealing with this effectively and immediately; it's not clear exactly how often anaesthetics cause anaphylaxis, but the best estimate is that a life-threatening allergic reaction occurs during 1 in 10,000 to 1 in 20,000 anaesthetics
  • death – there are approximately 10 deaths for every million anaesthetics given in the UK

Your risk of developing complications will depend on a number of factors, including:

  • your medical history – for example, whether you have any other serious medical conditions or illnesses
  • personal factors – for example, whether you smoke or are overweight; if you smoke, stopping several weeks before your operation will reduce your risk of having breathing problems, and losing weight will also help reduce your risk
  • the type of procedure – for example, whether it's a planned or an emergency procedure, or whether it's a major or minor procedure
  • the type of anaesthetic – local anaesthesia can have advantages over general anaesthetics in the right circumstances

Before your procedure, your anaesthetist will explain if there are any particular risks of developing possible complications.

In most cases, the benefits outweigh the risks. Any concerns you have should be discussed with your anaesthetist before surgery.

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.