Lumbar epidural anaesthesia and sensory profiles in term pregnant patients.

Sensory profiles of lumbar epidural anaesthesia were studied in 57 patients, during active labour. The local anaesthetics used were chloroprocaine three per cent with and without epinephrine, chloroprocaine two per cent, bupivacaine 0.25 per cent and a mixture of chloroprocaine three per cent and bupivacaine 0.5 per cent. A common pattern of spread was found for all local anaesthetic solutions with the onset of the block affecting the dermatomes innervated by the thinnest nerve roots (T12L1). There was a percentage of failure to block the thickest nerve root (S1). Inguinal and suprapubic discomfort ("missing segment") occurred when S1 was not blocked. Under the conditions of this experiment, the addition of bupivacaine to chloroprocaine did not increase the duration of the blockade significantly.