Local anaesthetic

Local Anaesthetic

A local anaesthetic is a medication which switches off nerves.  It is commonly used to switch off nerves whcih transmit pain signals and so causes anaesthesia.  Becuase this effect only occurs locally where the medication has been injected or applied it is called Local Anaeasthetic. 

Local anaesthetic can be used to make procedures like endoscopy more comfortable.  Or it can be used as part of the pain management for larger operations.  Some smaller operations can be performed with just local anaesthetic although this is often combined with sedation.

Types of local anaesthetic

Local anaesthetic can be applied in a number of ways; as a cream, a spray or by injection.  

The most commonly used cream is called EMLA.  This applied to the skin before injections or minor surgery to remove the pain of the injection.  It is very effective but takes a long time to work and so tends to be used more for children. 

There are two type of spray; 

Ethyl Chloride is sprayed onto the skin where it causes a very rapid (3 to 5 second) chilling effect.  Whilst the skin is chilled it is quite numb and so the sting of an injection or removal of a splinter and be avoided.  It is possible to peform very minor surgery but the numbing effect is very short lived, only 30 seocnds or so and then sensation returns.

Lignocaine (Xylocaine) Spray, this is a true local anaesthetic and when sprayed or dripped onto moist skin; the mouth and throat, the eye, the urethra or anus, produces a complete loss of sensation which may last for 2 hours or more.  Lignocaine can be used to make endoscopy more comfortable when sprayed into the mouth before a procedure.  It may also be used to make minor eye surgery painless.  Lignocaine comes in a number of forms and is the most commonly used local anaesthetic.

Injection.

Lignocaine and its close relative Marcaine are very powerful local anaesthetics when given by injection.  They can provide complete loss of sensation within a few minutes that will last for up to 8 hours.  Most patients will have experienced a local anaesthetic during a visit to the dentist and will know the feeling of numbness and also recognise that along with the numbness can be some weakness.  Local anaesthetic injection is used as an adjunct to many operations to reduce or remove pain completely.  This is especially true for all abdominal surgery, including hernia surgery, and all anal surgrery.  There are very few serious side effects to local anaesthetic when it is used properly, however muscle weakness is common and care must be taken immediatly after surgery especially if the anaesthetic has been injected near a limb as in hernia surgery.

Local anaesthetic can be injected directly into or onto a nerve causing anaesthesia in the whole body part supplied by that nerve or nerves.  This creates a region of anaesthesia and so is called regional anaesthesia.  Some common forms of this are Spinal and Epidural anaesthesia which can be used for hernia surgery and Caudal and Pudendal blocks which are used in anal surgery.  There are specialised techniques which your anaesthetist may discus with you were local anaesthetic is injected under ultrasound guidance.  This can give very accurate placement of the anaesthetic near to the nerve and so better pain relief.   A common form of this is the TAP block which is used after major abdominal surgery.

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