Safety and efficacy of a low volume extradural test dose of bupivacaine in labour.

A low volume of bupivacaine has been recommended as a "test dose" before extradural injection of local anaesthetic in labour. In order to test the safety and efficacy of this test procedure, the effects of bupivacaine 1.6 ml given by extradural injection were compared with those following the same dose given by the intrathecal route. Various indices of motor, sensory and autonomic block were recorded after injection in two groups of 20 healthy pregnant patients. Complete inability to raise the foot from the bed by hip flexion with the knee held straight was the only definite sign of intrathecal injection. In 10% of patients the final diagnosis could not be made until 10 min after injection. In 25% of patients hypotension occurred within 5 min of intrathecal injection despite preload with 1 litre of fluid i.v.