COMPARISON OF PLASMA BUPIVACAINE CONCENTRATIONS DURING CONTINUOUS EXTRADURAL INFUSION FOR LABOUR

In many centres, continuous extradural infusion of bupivacaine, for the maintenance of analgesia in labour, is now preferred to the use of in-termittent injections. The infusion provides a more stable level of analgesia, avoiding the inevitable painful episodes which can occur while waiting for the "top-up " dose to be given, and allows the use of lower concentrations of local anaesthetic [1]. Intermittent bolus doses can be associated with episodes of hypotension and produce peaks in the plasma concentrations of the local anaesthetic. Infusions are said to be safer if accidental subarachnoid or intravascular migra-tion of the catheter occurs [2]. The risk of total spinal block is reduced, the onset of symptoms and signs being more gradual than with bolus administration. While the clinical effects of continuous extra-dural infusion are well documented [3—5], there have been no reports relating plasma concen-tration to clinical response. We report a com-parison of plasma concentrations associated with the infusion of an 0.08 % and 0.25 % solution of bupivacaine given in the same dose per hour, and the clinical effects produced. PATIENTS AND METHODS Healthy women, at term, who requested extra-dural analgesia for labour were allocated randomly to receive either 0.08 % or 0.25 % solutions of bupivacaine by continuous infusion. They were receiving no medication, had no relevant past history and all had vertex presentations. Informe