Wednesday, 24 January 2018 06:08

Why do Local Anaesthetics Sting? Featured

Why Do Local Anaesthetics Sting?

It is one of the great ironies of life that Local Anaesthetics should cause a degree of pain before they start to work to block out further pain. Proving once again in life there is not such thing as a free lunch. But why do they sting when first injected?

There are multiple reasons. The local anaesthetic works to block the function of nerves carrying pain sensation but they take time to do this. During this period a number of things cause the pain.

Firstly there is the initial sting of the needle going in although with the very fine and sharp needles used today this is rarely much of a discomfort.

Next the injection of the local anaesthetic fluid expands the tissues it is injected into and this can cause pain. The doctor can reduce this pain by a slow injection and making sure the needle is positioned deep enough in the skin to allow this expansion.

Sometimes the low temperature of the local anaesthetic solution can cause pain so warming it up a bit before injection can help.

Finally, and probably the main cause of the pain, is that the local anaesthetic solution is more acidic than the body tissues. It has to be this way in order to preserve it in solution and allow it to be stored. The pain caused by this acidity can be reduced if the doctor mixes some sodium bicarbonate with it just before injection.

Although technique by the doctor is important, patient factors such as the site of the injection (the tip of the nose for example), the level of anxiety felt by the patient and a persons general tolerance for pain can all affect the level of discomfort felt. Reassurance and distraction by the doctor at the time of injection may assist to minimise some of this pain.