Pain Centre

05 December 2008

Local anaesthetics of post-operative pain relief, including Nerve Blocks

If the surgery is minor, like removal of a breastlump, infiltration of the surgical area with local anaesthetic will be sufficient analgesia.

Local infiltration:
If the surgery is minor, like removal of a breastlump, infiltration of the surgical area with local anaesthetic will be sufficient analgesia. For more major surgery, infiltration of the surgical wound will not be sufficient, but can contribute to pain relief, so that fewer other painkillers will be needed, with less risk for side-effects.

Nerve block or nerve plexus block:
The nerve supplying the surgical area can be blocked to render it insensitive, e.g. injecting local anaesthetic at the base of the toe to numb the whole toe for removal of an ingrown toenail.

A whole nerve bundle (called: plexus) can be blocked if a total limb or part of a limb needs to be anaesthetised. For the shoulder and upper arm, a single injection next to the brachial plexus in the neck can be given, for the forearm and hand, the same nerve bundle can be blocked where it runs through the armpit. The leg is different from the arm for anaesthesia because there are two different nerve bundles involved, one supplying the front and one for the back of the leg. This means that two separate injections have to be given.

The effect of the local anaesthetic wears off after 10 – 16 hours. If longer pain relief is required, the anaesthetist can place a catheter (a very thin plastic tube) next to the nerve bundle with his original injection. This catheter is very soft and flexible, so the patient is not aware it is there. Local anaesthetic can be run continuously through this catheter to maintain the nerve block for as long as necessary (days, or in the case of chronic pain, weeks or months).

The advantage of prolonged pain relief is that manipulation of the affected limb during physiotherapy can be done easily, which speeds up recovery.

The side-effects are very few. Some patients complain that the feeling of a numb, limp arm or leg is not pleasant, but the advantage is that the severe pain of the surgery is not felt.

For a nerve block to be successful, the local anaesthetic has to be injected right next to the nerve, but the needle should not touch the nerve because this can cause damage. Nerves and nerve bundles are very small, rarely more than one or a few millimetre in diameter. To accurately locate the nerve, the anaesthetist often uses a nerve stimulator.

This little device is connected to the needle with which the nerve block is done, and sends a tiny electrical current through it. This current stimulates the nerve and the visible effect is that the muscles innervated by this nerve or nerve bundle contract, without the patient having control over it. This is a strange feeling, but not painful at all. The use of a nerve stimulator greatly improves the success of the block and at the same time protects the nerve because it tells the anaesthetist when the needle is approaching the nerve too closely.

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