Infiltration anaesthesia

Local anaesthetic is injected subcutaneously. It acts on local nerve endings. Lignocaine 0.5% is the most commonly used agent, and it is often combined with adrenaline to retard dispersion and increase the local dose that may be given without systemic toxicity.

Infiltration anaesthesia is frequently used postoperatively around the site of a wound. Preoperatively, large volumes of weak local anaesthetic and adrenaline can be used to force apart tissue planes before the first incision.

Some practical considerations:

• know the maximal volume of the anaesthetic that may safely be injected for the patient's size
• repeatedly aspirate to ensure the needle is not intravascularly-sited
• after the initial injection, further injections should be made through the same area to the surroundings with a long needle
• always inject anaesthetic after insertion of the needle to the hilt and while it is being withdrawn
• when infiltrating dirty wounds, it may be preferable to inject through the skin rather than the wound edges
• adrenaline with local anaesthetic should be avoided in sites such as the digits and penis