TOXICITY OF LOCAL ANAESTHETICS

Toxicity of local anaesthetics has a direct effect on nervous tissue. This toxicity is determined by various factors such as site of injection, concentration of the agent and whether it is ionic or non-ionic. Also, additives of vasoconstrictive agents, both catecholamine and non-catecholamine may be used.

"All local anesthetic molecules at sufficient concentration are directly cytotoxic to nerve cells"(i)

Powell and Myers () assessed local anaesthetic toxicity on rat sciatic nerves and found that "both nerve injury and edema increased with concentration."

Burm () noted that epidural doses must be much higher than spinal doses, due to the uptake into extraneural tissues and systemic absorption.

Professor Ginther of UC Irvine Medical Centre mentions "peripheral neurotoxicity such as prolonged sensory and motor deficits" in his Internet discussion on toxicity of local anaesthetics. This has been hypothesised as being due to a combination of low pH and the preservatives such as sodium bisulfite in the mixture. Indeed, a recent case of adhesive arachnoiditis following bupivicaine containing preservatives was cited by Uefuji() in Japan.

Malinovsky () discusses the various causes of neurological lesions, including direct trauma of the spinal cord and nerve roots, compromised spinal cord perfusion and direct neurotoxic effect. He suggests that "neurotoxicity can result from decrease in neuronal blood supply, elicited by high concentrations of the solutions, long duration exposure to local anaesthetics, and the use of adjuvants."

He advocates several measures to reduce the incidence of neurotoxicity: use of the lowest efficient dose, avoidance of repeated or large volume injections and use of preservative-free solutions. As early as 1954, Moore () advised that local anaesthetic administered epidurally should be free of preservatives.

Table of Contents

Introduction
TOXICITY OF LOCAL ANAESTHETICS
NEXT: PREVIOUS SPINAL PROBLEMS
DURAL PUNCTURE
NEUROLOGICAL COMPLICATIONS OF EPIDURAL ANAESTHESIA
SHORT-TERM COMPLICATIONS
BACK PAIN FOLLOWING EPIDURAL ANAESTHESIA
LONG-TERM NEUROLOGICAL COMPLICATIONS
ARACHNOIDITIS CASES
CONCLUSIONS
References