Dose-response study of intrathecal fentanyl added to bupivacaine in infants undergoing lower abdominal and urologic surgery

Background: Intrathecal (IT) adjuncts often are used to enhance the duration of spinal bupivacaine. Fentanyl is a spinal analgesic that could be a useful adjunct, and enhances the duration and quality of sensory block in adult surgical and obstetric population. However, no data exist to assess the dose-response characteristics of IT fentanyl when added to bupivacaine in infants. Methods: Fifty-eight infants undergoing lower abdominal and urologic procedures were randomized into four groups to receive plain 0.5% hyperbaric bupivacaine F0 (< 5 kg = 0.5 mg.kg(-1); 5-10 kg = 0.4 mg.kg(-1)). Groups F0.25, F0.5, and F1 groups received bupivacaine added with 0.25, 0.5, and 1 mu g.kg(-1) of fentanyl, respectively. Duration of spinal anesthesia (SA) as assessed by the recovery of hip flexion in the postoperative period was the primary variable analyzed. In addition, the duration of analgesia in the postoperative period, rescue postoperative analgesic requirements and hemodynamic changes were recorded. Results: Fifty-six infants were studied. The four groups were similar for age, weight, duration of surgery, onset of sensory, motor block, and the highest level of analgesia attained. The addition of 1 mu g.kg(-1) fentanyl (F1) significantly increased the duration of SA (74.27 +/- 6.1 min) compared to the control group (51.21 +/- 5.2 min) (P = 0.001). Postoperative pain-free interval was prolonged (P = 0.004) and significantly less rescue analgesics were required after 1 mu g.kg(-1) IT fentanyl (P = 0.032). These parameters did not show any significant difference among groups F0, F0.25, and F0.5. Conclusions: The addition of 1 mu g.kg(-1) IT fentanyl to spinal bupivacaine prolonged the duration of spinal block in infants undergoing lower abdominal and urologic procedures.