Can pre-emptive interpleural block reduce perioperative anesthetic and analgesic requirements?

BACKGROUND AND OBJECTIVES: The hypothesis that preoperative interpleural block might reduce intraoperative anesthetic and analgesic requirements and modify the intensity of postoperative pain was examined in this double-blind, randomized, saline-controlled study.

METHODS: Thirty women undergoing cholecystectomy with subcostal incision were included. All patients received a background isoflurane anesthetic in 40% O2 and air. Interpleural catheters were inserted after induction of anesthesia and 20-25 minutes before surgical incision. Patients were randomly allocated to one of two groups. Group 1 received a bolus of 0.5% plain bupivacaine followed by a continuous infusion of 7 mL/h 0.25% bupivacaine. Group 2 received similar bolus volume and infusion of 0.9% saline. The attending anesthesiologist was blinded to patient groups. Intraoperative analgesia was assessed by the hemodynamic responses to surgery and by the anesthetic and analgesic requirements. Postoperative analgesia was accomplished by 20 mL bupivacaine 0.5% in group 2 patients followed by an infusion of bupivacaine 0.25% in the two groups. Postoperative analgesia was assessed by visual analog scale (0-10), hourly bupivacaine requirements, peak expiratory flow rate, and the request for additional intramuscular morphine.

RESULTS: Preoperative interpleural block produced a significant decrease in mean arterial pressure and heart rate. These hemodynamic changes were partly corrected by surgical incision and reduction of isoflurane concentration. The mean intraoperative isoflurane requirements in group 1 and 2 were, respectively, 0.59 +/- 0.02% and 1.2 +/- 0.12% (P < .001). Preoperative instillation of bupivacaine in the pleural space resulted in about 50% reduction in isoflurane requirements. Intraoperative alfentanil requirements were 13.6 +/- 6 and 29.2 +/- 11 micrograms/kg in the bupivacaine and saline groups, respectively (P < .001). After the operation, both study groups had comparable visual analog scale peak expiratory flow rate, bupivacaine infusion rate, and intramuscular morphine supplements.

CONCLUSIONS: Preoperative interpleural block, during a background isoflurane anesthetic, reduces the hemodynamic response to surgery and the intraoperative anesthetic and analgesic requirements. Preoperative interpleural block with plain bupivacaine results in significant reductions in mean arterial pressure and heart rate, probably related to unilateral sympathetic block and the concomitant use of isoflurane. The timing of interpleural block, that is, pre-emptive versus postoperative, does affect the intensity of postoperative pain or the request for supplementary analgesia.