CAN PREEMPTIVE INTERPLEURAL BLOCK REDUCE PERIOPERATIVE ANESTHETIC ANDANALGESIC REQUIREMENTS

Background and Objectives. The hypothesis that preoperative interpleur al block might reduce intraoperative anesthetic and analgesic requirem ents and modify the intensity of postoperative pain was examined in th is 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% O-2 and air. Interpleural catheters were inserted after induction of anest hesia and 20-25 minutes before surgical incision. Patients were random ly allocated to one of two groups. Group 1 received a bolus of 0.5% pl ain bupivacaine followed by a continuous infusion of 7 mL/h 0.25% bupi vacaine. Group 2 received similar bolus volume and infusion of 0.9% sa line. The attending anesthesiologist was blinded to patient groups. In traoperative analgesia was assessed by the hemodynamic responses to su rgery and by the anesthetic and analgesic requirements. Postoperative analgesia was accomplished by 20 mL bupivacaine 0.5% in group 2 patien ts followed by an infusion of bupivacaine 0.25% in the two groups. Pos toperative analgesia was assessed by visual analog scale (0-10), hourl y bupivacaine requirements, peak expiratory now rate, and the request for additional intramuscular morphine. Results. Preoperative interpleu ral block produced a significant decrease in mean arterial pressure an d heart rate. These hemodynamic changes were partly corrected by surgi cal incision and reduction of isoflurane concentration. The mean intra operative 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 i n isoflurane requirements. Intraoperative alfentanil requirements were 13.6 +/- 6 and 29.2 +/- 11 mu g/kg in the bupivacaine and saline grou ps, respectively (P <.001). After the operation, both study groups had comparable visual analog scale peak expiratory now rate, bupivacaine infusion rate, and intramuscular morphine supplements. Conclusions. Pr eoperative interpleural block, during a background isoflurane anesthet ic, reduces the hemodynamic response to surgery and the intraoperative anesthetic and analgesic requirements. Preoperative interpleural bloc k with plain bupivacaine results in significant reductions in mean art erial pressure and heart rate, probably related to unilateral sympathe tic block and the concomitant use of isoflurane. The timing of interpl eural block, that is, pre-emptive versus postoperative, does affect th e intensity of postoperative pain or the request for supplementary ana lgesia.