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Canadian Journal of Anesthesia, Vol 33, 537-541, Copyright © 1986 by Canadian Anesthesiologists' Society

Effect of pH-Adjustment of Bupivacaine on Onset and Duration of Epidural Analgesia in Parturients

GRAHAM H. McMORLAND MB CHB FRCPC1, M. JOANNE DOUGLAS MD FRCPC1, WAYNE K. JEFFERY MSC1, PEGGY L E. ROSS MD BSC(Med) FRCPC1, JAMES E. AXELSON PHD1, JAMES H K. KIM MD FRCPC1, DAVID R. GAMBLING MB BS FRCPC1, and KERRI ROBERTSON MD1

1 Department of Anaesthesia, Faculty of Medicine and Faculty of Pharmaceutical Sciences, University of British Columbia and Grace Hospital, Vancouver, British Columbia

Address correspondence to: Dr. G.H. McMorland, Department of Anaesthesia, Grace Hospital, 4490 Oak Street, Vancouver, B.C. V6H 3V5.

Previous studies have reported that elevation of the pH of local anaesthetics is associated with enhanced quality and duration of block. This study investigated the effect, on time to onset and duration of analgesia, of pH adjustment of 0.25 per cent bupivacaine immediately prior to injection into the epidural space in parturients. Addition of 0.1 ml of 8.4 per cent sodium bicarbonate to 20 ml of 0.25 per cent bupivacaine consistently raised the pH of the local anaesthetic from 5.65 to 7.26 (mean values).

Thirty parturients received an epidural injection of 8 ml of pH-adjusted 0.25 per cent bupivacaine and a control group of 30 parturients received 8 ml of the standard commercial preparation of 0.25 per cent bupivacaine. Elevation of the pH of the local anaesthetic significantly increased the speed of onset of analgesia from 6.0 minutes to 3.2 minutes and the duration of analgesia was significantly lengthened from 79.4 minutes to 96.5 minutes. There was no significant influence on time to peak effect, nor on mean maternal plasma levels of bupivacaine.

Key Words: ANAESTHESIA: obstetric, epidural • LOCAL ANAESTHETICS: bupivacaine






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Copyright © 1986 by the Canadian Anesthesiologists' Society.