Effect of extradural bupivacaine or i.v. diamorphine on calf blood flow in patients after surgery.

Strain gauge venous occlusion plethysmography was used to measure arterial flow, venous capacity and maximum venous outflow in the calves of seven patients undergoing gynaecological surgery. Plethysmography was performed before surgery, before, and for 30 min after, the extradural injection of 0.5% bupivacaine. On the morning after surgery, 0.5% bupivacaine was injected extradurally and plethysmography performed. With regression of the extradural blockade and the re-emergence of pain, analgesia was produced with diamorphine i.v. and plethysmography repeated. Control measurements were also made. Compared with a mean control value of 100% (3.4 ml dl-1 min-1) calf arterial flow increased from 160% to 285% after the preoperative extradural blockade, and from 123% to 191% following the postoperative analgesic extradural blockade, but there was no significant change when pain was relieved after i.v. diamorphine. Mean arterial pressure changed insignificantly after all the injections. No significant changes were measured in venous capacity or maximum venous outflow.