Anaesthetic Specialities

Regional Anaesthesia

Regional anaesthesia, as the name implies, refers to a group of techniques that anaesthetise only a specific region of the body.

Simple enough, but to understand how it works one needs to have a basic idea of the way the human body is wired. Nerves start as millions of bits of flayed wire (receptors) that are stuck under the skin and other tissues. These fire an electric current when they are excited (by cold, heat, pinprick etc.). The nerves (or ‘wires’) take electric currents up through the spinal cord (the ‘mains cable’) to the brain (the ‘computer or processing unit’).

Interestingly, the brain, despite being the ‘seat’ of pain, is a wobbly mass of jelly that does not feel pain itself. Indeed, operations on specific parts of the brain are sometimes carried out with the patient fully awake.

With a general anaesthetic we effectively turn off most of the brain. This stops the patient feeling pain, but also abolishes other functions. For example, many types of general anaesthetic will stop a patient’s breathing. This important function can be easily entrusted to a machine. However, if the patient has a bad chest (for example from cigarette smoking or a recent infection) a general anaesthetic may be unsafe or risky.

With regional anaesthesia we can block the electrical impulses going to the brain before they actually reach it. So if the brain does not receive these messages, there is effectively no pain. You can have a finger sliced off, and if the brain does not get told about it then it may as well not have happened.

For a small skin operation, or a tooth extraction, we can block the flayed wires (receptors) thus stopping the pain impulses from forming.

We can also block the wires (nerves) or, in certain areas, bundles of them (plexuses). This is what anaesthetists do when we perform what is known as a ‘nerve block’. The procedure involves locating a specific nerve or plexus, using one of various methods, and using a needle to deposit local anaesthetic around it. The simplest of these are ‘landmark’ techniques, whereby the anaesthetist applies his or her knowledge of anatomy to locate the nerves. Nowadays we use ultrasound technology to actually visualize specific nerves on a screen. This recent advance has opened up a new world of regional block techniques.

Anaesthetists can also block pain impulses at the level of the ‘mains cable’, or spinal cord. This is what we do when we perform a spinal or an epidural. If we block the spinal cord at the middle of the back, we block all electric currents from the lower body. This means that an operation such a Caesarean section can be carried out painlessly whilst the patient remains fully awake.

There are side effects, as well as risks and complications associated with regional anaesthesia.

When we carry out a nerve block, we usually block muscle movement as well as sensation. This is an example of a side effect that is difficult to work around. The nerves that carry sensation to the brain also contain fibres that transmit data from the brain to the muscles, instructing them them to move. When that communication is cut off, muscles are paralysed. Up till a few decades ago patients used to lie in bed for several weeks following a major operation. For example, after a hip replacement patients needed six weeks in traction, unable even to turn in bed. Nowadays they are encouraged to walk less than a day after the operation. Of course, this has been made possible with newer types of surgery and the use of modern hi-tech materials, leading to greatly improved results. The emphasis on early mobilisation has led to the development of methods whereby we block smaller and smaller individual nerves that contain more pain fibres and less or no motor fibres. Also, some local anaesthetics are being developed that block pain fibres in preference to motor ones.

Some side effects are specific to the type of regional anaesthetic that is being carried out. For example, a spinal anaesthetic is often associated with a drop in blood pressure (causing light-headedness if not treated promptly).

Very rarely, structures close to the site of injection can be damaged. For example, an injection at the top of the chest to numb nerves going down into the arm can be associated with injury to the lung (which is close by). These are becoming very uncommon with advances in ultrasound technology and anaesthetists that are more experienced at using it.

Despite our many precautions, sometimes the nerve itself can be damaged by the needle or by the local anaesthetic itself. This can take a few weeks to resolve, in which case it is considered ‘temporary’, or the function of the nerve may recover after several months or never recover fully at all. This is considered ‘permanent’ and is extremely rare

Other extremely rare side effects include an allergic reaction to the local anaesthetic, or a reaction where too much local anaesthetic enters the bloodstream causing toxicity.

Although it is important to be properly informed of the possible risks, the alternative is often either remaining in pain or receiving strong intravenous pain-killers. These two alternatives are also, in themselves, related to their own side-effects and risks.

It is important to note that regional anaesthesia does not necessarily replace a general anaesthetic. The two often work hand in hand, with the general anaesthetic providing pain relief for the surgery itself, and the regional anaesthetic serving to provide post-operative comfort for several hours (even days).

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