Anaesthetics work by blocking the signals sent along your nerves to your brain. Nerves are bundles of tiny fibres that use chemical and electrical signals to pass information around your body.

Anaesthetics work by stopping the nerve signals that keep you awake and aware from reac​hing 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.

As well as local and general anaesthetic, there are a number of other types of anaesthesia. Unlike general anaesthetic, these do not 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 defined region of your body, usually served by a large nerve bundle (such as your arm), giving numbness or pain relief for deeper operations where more extensive numbness is needed.
   
• Epidural anaesthetic - a type of regional anaesthetic usually used to numb the lower half of the body and good for pain relief - for example, 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 that surgery can be safely carried out in this area.
   
• Sedation - medication that makes you feel sleepy and relaxes you both physically and mentally, it is 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. 

An anaesthetic can be given in a number of ways. It can be given in the form of:

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

Anaesthetists are doctors who have received specialist training in anaesthesia. They will 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 are having
   
•  any risks or side effects associated with different types of anaesthetic
   
• they will also 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 are unsure about, and raise any queries you have. Your anaesthetist will carefully monitor you throughout your operation and will make sure you wake up comfortably afterwards. They may also help with any pain relief you might need following the procedure.

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 any side effects. 

Some of the 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 do not usually last very long and some of them can be treated if necessary. You should tell the healthcare professionals treating you if you experience any of the above side effects or if you are in pain after your procedure.

In recent years, having anaesthesia has become extremely safe. Advances in equipment, medication and training mean serious problems are rare. As with surgery and any medical procedure, however, there is a potential risk of complications. The benefits and risks to surgery and anaesthesia will be carefully weighed up and explained to you before you have any operation. Very rare possible complications include:

• ​​​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
   
• permanent nerve damage - which can cause numbness or paralysis (inability to move a part of the body), although this may be a result of the surgery itself
   
• death - there are approximately ten 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; likewise, losing weight will help reduce your risk)
   
• the type of procedure - for example, whether it is a planned procedure or an emergency procedure, or whether it is 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.

(Text supplied via NHS Choices)​