[Postoperative analgesia with tramadol. Continuous infusion versus repetitive bolus administration].

Postoperative pain relief can be achieved by several methods, including the use of systemic opioids and regional anaesthesia with intrathecal or epidural opioids or local anaesthetics. On-demand analgesia using a PCA (patient-controlled analgesia) system is regarded as the ideal option for systemic opioid analgesia. While PCA devices are not yet commonly used in all recovery units, the use of repetitive boluses on demand is still the most frequent form of administration in postoperative pain therapy. The objective of the present study was to show if continuous infusion of the opioid tramadol could produce better analgesia than repetitive administration of boluses. METHOD. In a study under double-blind conditions 135 ASA I and II patients were assigned at random to group I (infusion group) or group B (bolus group) when they first requested pain treatment after abdominal surgery. The patients in group I received an initial intravenous loading dose of 100 mg tramadol, followed by an infusion of 12 mg/h tramadol for 24 h; if necessary, repeated boluses of 50 mg tramadol were given. In group B the patients received a placebo infusion instead of the tramadol infusion; otherwise, the procedure was the same. Pain relief was monitored by means of a VAS (visual analogue scale) up to 6 h after surgery. We investigated the retrograde assessment of analgesia by the patients after 6 h, how often repetitive boluses were required, and the amount of analgesics administered in 6 and 24 h. RESULTS. The pain relief was assessed as excellent or good by 76.5% of group I and 65.6% of group B; 19.1% of group I and 26.9% of group B assessed the analgesic effect as satisfactory; 4.4% of group I and 7.5% of group B complained of insufficient analgesia. In group I 69.2% requested only one or no repetitive bolus, compared with 40.3% in group B, while two or more boluses were demanded by 30.8% in group I und 59.7% in group B. The average analgesic consumption after 6 h was 223.5 +/- 53.7 mg tramadol in group I and 176.6 +/- 63.1 mg tramadol in group B, respectively. After 24 h it was 449.5 +/- 66.0 mg tramadol in group I and 201.6 +/- 83.9 mg tramadol in group B. While the consumption during the first 6 h was comparable, from then on the consumption in group I increased significantly. Side effects were reported by 25% in both groups. They were clinically irrelevant and did not necessitate termination of the clinical trial in any case. During the study period pulse and blood pressure remained within the normal range and did not show any significant changes. CONCLUSION. The fact that the patients in group I requested far fewer repetitive boluses than those in group B and the assessment by the patients led to the conclusion that treatment in the infusion group is better than that in the bolus group. Concerns that a significantly higher consumption of analgesics would cause unwanted side-effects have proven unfounded. Six hours after surgery, when analgesia was evaluated by the patients, there was no significant difference between the two groups. Not until the maintenance infusion had been administered for a further 18 h, was the tramadol consumption within the infusion group significantly higher. Thus, we should consider continuing unreduced administration of the maintenance infusion 6 h after operation.