[Preemptive analgesia in cholecystectomy using pethidine]

Preemptive analgesia given before noxious stimulation prevents or reduces subsequent pain. Pain associated with central sensitization is called pathological pain. Preemptive analgesia could be defined as analgesia that prevents the development of pathological pain. The clinical significance of central sensitization lies in prediction that preemptive analgesia may prevent the establishment of central sensitization and reduce pain experienced following peripheral injury. Various pharmacological agents and methods have a potential in prevention of acute postoperative pain by blocking the somatosensory system and abolishing hypersensitivity. But the role of preemptive analgesia in postoperative pain is still controversial. The goal of the present study was to examine whether pethidine administration before skin incision is more effective in reducing postoperative pain than the same dose of pethidine given intraoperatively.

Thirty patients (ASA 1 to 2), aged from 40 to 65 years, admitted for elective laparotomic cholecystectomy entered the study. Group 1 (n = 15) received 1 mg/kg of pethidine i.v. 5 minutes before induction of anaesthesia (before skin incision) and 0.9% NaCl of equal volume intraoperatively (after peritoneal opening). Group 2 (n = 15) received pethidine and 0.9% NaCl in a reverse manner. Premedication was omitted. No other analgesics were administered at induction and intraoperatively. Anaesthesia was induced with midazolam, thiopentone and succinylcholine for tracheal intubation. Pancuronium was administered for muscle relaxation and halothane with O2/N2O for maintenance of anaesthesia. The duration of surgery (time from skin incision to skin closure) and time from skin closure to the first analgesic request were measured and recorded. In the ward, patients were given metamizol (2500 mg) i.m. at request during the first 12 h. If the regimen was not sufficient, piritramide (2 mg) i.m. was given at request. The intensity of pain was estimated before the first analgesic request and 4, 8, 12 and 24 h thereafter. Pain scores were recorded using VAS (0 = no pain; 10 = worst pain). Data are presented as mean values with their standard deviations and as the ranges of each parameter. The differences in data between two groups were evaluated with Student's t-test. P > 0.05 was considered statistically significant.

Demographic data, duration of surgery and time from skin closure to the first analgesic request are presented in Table 1. No significant difference was found between the two groups. The postoperative analgesic requirements in two groups were similar and piritramide requirement was omitted. VAS scores at each time (Table 2) did not differ between the two groups.

The findings of many clinical investigations remain controversial. Some clinical studies comparing the same analgesic intervention before and after the painful stimulus have shown a benefit of preemptive analgesia. The results of our study did not show a significant difference in pain scores neither in analgesic requirements of patients who received systemic pethidine before the painful stimulus compared with the patients treated with the opioid intraoperatively. However, epidural opioid administration may be more effective (17,18). It is important to say that inhalational anaesthetics, including N2O and some i.v. anaesthetic agents may have preemptive effects themselves, significantly reducing spinal sensitization (19,20). In clinical studies when the preemptive effect of analgesics is under investigation, inhalational and i.v. anaesthetics which are administered to induce and maintain anaesthesia are given before surgery. Therefore development of central sensitization may be attenuated or prevented by the anaesthetics overlapping the preemptive effect of analgesics.

The results of this study did not demonstrate a preemptive effect of pethidine. (ABSTRACT TRUNCATED)