Post-operative analgesia after remifentanil-based anaesthesia

Remifentanil is a very potent ultrashort acting opioid, that is mainly used as a part of balanced anaesthesia regimens for management of intraoperative pain. Effective plasma levels of this drug can only be maintained using continuous infusions, as tissue esterases inactivate remifentanil within minutes following its application. The advantages of this specific pharmacokinetic behaviour are that no accumulation occurs and that patients wake up very rapidly independent of a functioning metabolism and duration of infusion. Further plasma levels can be titrated to effect very rapidly. On the other hand will the rapid offset of analgesia during awakening from anaesthesia lead to dangerous cardiovascular changes due to mainly sympathoadrenal changes as a consequence of pain. The study discussed here was performed in order to compare two possible strategies to reduce immediate postoperative pain (and thus cardiovascular changes) following remifentanil-sevoflurane anaesthesia. Sixty patients undergoing major abdominal surgery were randomly allocated to receive 20 minutes before the end of surgery either sufentanil (S) 0.15 mcg/kg or tramadol (T) 100 mg/patient i.v. A blinded observer scored sedation following extubation and assessed pain using a verbal rating score (VRS) at awakening and 5, 10, 30, 60 minutes afterwards. Blood pressure (monitored indirectly), heart rate and rate pressure product were recorded before surgery, during surgery, at extubation, and 5, 10, 30, and 60 minutes thereafter. Significant differences between the groups were the following: heart rate was lower with sufentanil 5 minutes following extubation (mean 78 vs 86); rate pressure product was lower with sufentanil at extubation and five minutes later; verbal rating score values were significantly lower with sufentanil 5 and 10 minutes following extubation. No other significant differences regarding measured values or side effects were noted. In order to avoid overdosing and consecutively severe respiratory depression patients receiving sufentanil were dosed per kg. Tramadol on the other hand was dosed per patient. As bodyweight ranged from 58-90 kg, this resulted in a relatively wide dose range per kg. It is possible that individual patients were underdosed. This may have contributed to the fact that verbal rating score values and rate pressure product were higher for T following the first 10 minutes following extubation. The study demonstrated that both drugs represent a possibility for postoperative pain control following remifentanil. The use of sufentanil dosed per kg was better in controlling pain and occurring increases in cardiovascular variables than tramadol dosed per patient. But the differences were only moderate and very short lived. If an adequate dosing of tramadol per kg instead of per patient would have influenced the outcome remains to be tested. Further it would be interesting to compare analgesia in the two groups for a longer postoperative time period.