Background Recent research has revealed that opioids can act directly on the peripheral terminals of afferent nerves to mediate antinociception. The aim of this study was to assess the influence of peripheral morphine administration on the nociception process in the postoperative period.

Methods One hundred fifty patients for laparoscopic cholecystectomy were randomly divided into 5 groups. Group M patients (n = 30) received local infiltration at trocar insertion points with 2 mg morphine in 20 mL of 0.9% NaCl solution (5 mL of solution per point) 10 minutes before the operation. For group B patients (n = 30), the solution used for infiltration was 20 mL of 0.25% bupivacaine; for group M+B patients (n = 30), the solution was 2 mg morphine in 20 mL of 0.25% bupivacaine; and for group S patients (n = 30), the solution was 20 mL 0.9% NaCl. For group S+M patients (n = 30), trocar insertion points were infiltrated with 20 mL of 0.9% NaCl, and patients in this group were given 2 mg of subcutaneous morphine 10 minutes before the surgery. Postoperative analgesic therapy was provided by on-demand analgesia with tramadol. After surgery, the following were measured: pain intensity scored on the visual analog scale, total tramadol requirement, time from the end of the surgical procedure to the administration of the first dose of tramadol, and the frequency of undesirable side effects (sedation, nausea, and vomiting).

Results Pain intensity and total tramadol requirement after surgery were lower in groups M, B, and M+B compared with groups S and S+M, but these differences were not statistically significant. The time from the completion of the operation to the administration of the first dose of tramadol was significantly longer in groups M, B, and M+B compared with groups S and S+M.

Conclusion Results of the study confirm the possibility of modifying the nociception process in the postoperative period through peripheral opioid administration.