Clinical experimental studies of postoperative infusion analgesia.

Thirty postoperative patients, after undergoing abdominal hysterectomy and standard general anesthesia, were randomly allocated to three groups and received, in the recovery ward, a continuous infusion of either pentazocine, piritramide, or ketamine. The patients rated their pain on a 15-cm visual analog scale. Patients in group 1 received pentazocine. Mean dosage was 0.12 mg/kg/hr on the day of operation, 0.1 mg/kg/hr on the first postoperative day, and only 0.07 mg/kg/hr on the second postoperative day. Pentazocine blood levels averaged 50 micrograms/L. Patients in group 2 received piritramide. Mean dosage was 0.038 mg/kg/hr on the day of operation, 0.024 mg/kg/hr on the first postoperative day, and 0.019 mg/kg/hr on the second postoperative day. Blood levels of piritramide were not determined because no satisfactory assay is available. Patients in group 3 received ketamine. Mean dosage was 0.32 mg/kg/hr on the day of operation, 0.28 mg/kg/hr on the first postoperative day, and 0.29 mg/kg/hr on the second postoperative day. Ketamine blood levels ranged between 120 and 180 micrograms/L. None of the three analgesics caused any important hemodynamic or respiratory side effects. Pentazocine and piritramide were more effective analgesics than ketamine was. Ketamine also had a higher incidence of side effects.