Tramadol 2.5 mg x kg(-1) appears to be the optimal intraoperative loading dose before patient-controlled analgesia.

Purpose: We previously established that a 5 mg x kg(-1) intraoperative dose can reduce the nausea/vomiting associated with tramadol patient-controlled analgesia (PCA). This study was conducted to identify the most appropriate initial dose to improve the quality of tramadol PCA.
Methods: During general anesthesia, 60 patients undergoing knee arthroplasty were randomly allocated to receive 1.25 mg x kg(-1) (Group I), 2.5 mg x kg(-1) (Group II), 3.75 mg x kg(-1) (Group III), or 5 mg x kg(-1) (Group IV) tramadol. The emergence condition was recorded. The titration of additional tramadol 20 mg + metoclopramide 1 mg doses by PCA every five minutes was performed in the postanesthesia care unit (PACU) until the visual analogue scale (VAS) score was < or = 3. An investigator blinded to study group recorded the VAS and side effects every ten minutes.
Results: In the PACU, significantly more tramadol (8.4 +/- 3.1 vs 4.3 +/- 2.1, 2.5 +/- 1.8, and 0.4 +/- 0.3, P < 0.05), and a higher incidence (15/15 vs 5/15, 3/15, and 2/15, P < 0.05) of PCA use was observed in Group I compared to Groups II-IV. VAS was significantly higher in Group I than in Groups II-IV at zero and ten minutes (P < 0.05). Unexpected delayed emergence anesthesia (> 30 min) was observed in Group III (n = 1) and in Group IV (n = 2). Sedation was more important in Groups III and IV than in Groups I and II (P < 0.05).
Conclusion: When considering efficacy and side-effect profile, 2.5 mg x kg(-1) of tramadol is the optimal intraoperative dose of this drug to provide effective postoperative analgesia with minimal sedation.