Basic plastic surgery techniques and principles: Using local anaesthetics

Toxicity

The potency of local anaesthetics in blocking neurones applies to other excitable cells. Neurones in the brain and conduction pathways in the heart are affected in the same way as peripheral nerves if enough of the drug enters the bloodstream.4 Absorption from the tissues into the circulation is dependent on several factors:5

• Total dose of drug

• Choice of drug--for example, lignocaine is more readily absorbed than prilocaine6

• Site of injection--sites with more blood vessels will absorb blood from the tissues quicker7

• Use of vasoconstrictors--some formulations contain additives like adrenaline which shut down the blood vessels in the area of injection and slow absorption.

Once an anaesthetic enters the bloodstream, the body breaks it down. Some drugs contain an ester link which is broken down by plasma pseudocholinesterases.8 Most anaesthetics that are used today contain an amide link instead of an ester link, and are broken down in the liver.9