PREEMPTIVE ANALGESIA - CLINICAL-EVIDENCE OF NEUROPLASTICITY CONTRIBUTING TO POSTOPERATIVE PAIN

Recent evidence suggests that surgical incision and other noxious perioperative events may induce prolonged changes in central neural function that later contribute to postoperative pain. The present study tested the hypothesis that patients receiving epidural fentanyl before incision would have less pain and need fewer analgesics postoperatively than patients receiving the same dose of epidural fentanyl after incision. Thirty patients (ASA physical status 2) scheduled for elective thoracic surgery through a posterolateral thoracotomy incision were randomized to one of two groups of equal size and prospectively studied in a double-blind manner. Epidural catheters were placed via the L2-L3 or L3-L4 interspaces preoperatively, and the position was confirmed with lidocaine. Group 1 received epidural fentanyl (4-mu-g/kg, in 20 ml normal saline) before surgical incision, followed by epidural normal saline (20 ml) infused 15 min after incision. Group 2 received epidural normal saline (20 ml) before surgical incision, followed by epidural fentanyl (4-mu-g/kg, in 20 ml normal saline) infused 15 min after incision. No additional analgesics were used before or during the operation. Anesthesia was induced with thiopental (3-5 mg/kg) and maintained with N2O/O2 and isoflurane. Paralysis was achieved with pancuronium (0.1 mg/kg). Postoperative analgesia consisted of patient-controlled intravenous morphine. Visual analogue scale pain scores were significantly less in group 1 (2.6 +/- 0.44) than in group 2 (4.7 +/- 0.58) 6 h after surgery (P < 0.05), by which time plasma fentanyl concentrations had decreased to subtherapeutic levels (< 0.15 ng/ml) in both groups. Patient-controlled morphine usage in group 2 (26.1 +/- 5.2 mg) was significantly (P < 0.008) greater than in group 1 (11.7 +/- 2.2 mg) between 12 and 24 h after surgery, even though visual analogue scale pain scores at these times were not significantly different (P > 0.05). The results suggest that preemptive analgesia may reduce the central consequences of surgical incision and rib retraction by preventing noxious neural impulses from gaining entry into the central nervous system.