Evaluation of local anaesthetic agents for regional anaesthesia in obstetrics.

The selection of a local anaesthetic agent for use in obstetrics must be based upon a more critical examination of its characteristics than is necessary in non-obstetrical cases. A short latency and great effectiveness in establishing sensory anaesthesia are of utmost importance in view of the high incidence of obstetric emergencies. Motor blockade is unnecessary for vaginal deliveries, except in premature childbirth when perineal relaxation becomes desirable. Systemic toxicity of local anaesthetics has a direct bearing on the clinical condition of the neonate especially after paracervical or prolonged extradural anaesthesia. The foetus appears very sensitive to only moderately elevated plasma concentrations of local anaesthetic. Addition of adrenaline to solutions of local anaesthetic agents with a pronounced vasodilating effect prolongs the anaesthesia, may reduce drug concentrations in the plasma, and negatively affects the strength and frequency of uterine contractions.