[Tramadol in postoperative pain therapy. Patient-controlled analgesia versus continuous infusion]

Patient-controlled analgesia (PCA) is a well-proven procedure for individual pain relief in the post-operative period. Despite its superior approach regarding pharmacokinetic and pharmacodynamic considerations, PCA equipment is not available to many in the clinical practice. The goal of this study was to compare the efficacy and safety of PCA with continuous infusion (CI), an easily feasible method, using tramadol (T) as a centrally acting opioid with minor side effects on circulation and ventilation.

The study was conducted on 20 ASA I or II patients aged 20-60 years undergoing gynecological operations under standardized general anesthesia. They were randomly allocated to two groups receiving i.v. T for postoperative pain relief via Lifecare PCA 4200 Infuser. Group 1 (G1, PCA, n = 10): loading dose 3 mg/kg T, demand dose 30 mg T, lock-out time 5 min, concurrent infusion 5 mg/h T; group 2 (G2, CI, n = 10): loading dose 3 mg/kg T, continuous infusion 0.35 mg/kg per h T. If the analgesia was inadequate, additional doses of 50 mg T were available in G2. During a mean trial period of 20 h, the heart rate, blood pressure, respiratory rate and blood gas analysis were documented. The plasma levels of T and beta-endorphins were determined. The quality of analgesia was assessed by using a verbal and a visual analogue scale.

The mean applied doses of T were 339 +/- 100 mg and 364 +/- 46 mg (G1 and G2, respectively) after 6 h and 565 +/- 243 mg and 707 +/- 139 mg (G1 and G2, respectively) in total (NS). Interindividual differences were substantial in G1. Five patients in G2 required an additional dose of 50 mg T. Pain scores decreased rapidly in both groups. The pain relief achieved was comparable and excellent after 6 h. The next morning, G2 reported significantly better analgesia in accordance with the higher availability of T as CI during the sleeping period. Mean plasma T levels were 994 +/- 440 ng/ml and 1170 +/- 357 ng/ml (G1 and G2, respectively). No correlation was found between T-levels and pain scores. The plasma levels of beta-endorphins were substantially elevated after the operation. They returned to normal during T-administration in both groups. No correlation was found between plasma levels of beta-endorphins and pain scores or T-consumption. Hemodynamic changes were minor and without clinical significance. PaO2 and paCO2 remained within small deviations from the physiological range. The respiratory rate, which was initially increased, dropped slightly in both groups. A high incidence of nausea and vomiting was observed, starting in the early phase of the loading dose.

T is well suitable for postoperative pain relief after major gynecological surgery using both PCA and CI. PCA ensures adjustment of the medication to the individual demand, whereas CI provides better analgesia after sleeping periods. We recommend antiemetic prophylaxis before treatment with T.