Influence of pre-emptive versus preventive analgesia with oral acetaminophen on postoperative pain in painful ophthalmic surgeries: which one is better?

Patients undergoing certain ophthalmic operation are more likely to experience serious postoperative pain. This study was carried out to evaluate the effects of pre-emptive vs. preventive analgesia with oral acetaminophen on postoperative pain in painful ophthalmic surgeries. In a double blind clinical trial, 60 patients undergoing strabismus, retinal detachment or deep vitrectomy were randomized into three equal groups. The first group (G1) received oral acetaminophen one hour before induction of general anesthesia and placebo postoperatively. The second group received placebo before induction and acetaminophen after the operation (G2). The third group received placebo at both times (G3). Blood pressure, heart rate and occurrence of oculocardiac reflex (OCR) were recorded during the operation. Pain score (VAS: visual analog scale), the time of the first analgesic use (in hours), and total analgesic requirement (acetaminophen: mg) were determined until 24 hours postoperatively. Data was analyzed using ANOVA, Chi-2 and Kruskal-Wallis tests. The mean pain score was lower in G1 compared with G2 at 2 and 24 hours after the operation (2.1 ± 0.6 vs. 2.7 ± 0.4, P = 0.001 and 1.1 ± 0.3 vs. 1.5 ± 0.5, P = 0, respectively). The pain score at 2, 6 and 24 hours after the operation was greater in G3 compared with G1 (2.8 ± 0.3 vs. 2.1 ± 0.6, P = 0, 2.3 ± 0.7 vs. 1.7 ± 0.5, P = 0 and 1.6 ± 0.4 vs. 1.1 ± 0.3, P = 0.001, respectively). There was no significant difference among the three groups with respect to the intraoperative hemodynamic changes, occurrence of OCR, the time of the first analgesic use and analgesic consumption. The use of oral acetaminophen as pre-emptive analgesia one hour before painful ophthalmic surgeries may reduce postoperative pain intensity.