BACKGROUND: Intrathecal opioid, a useful adjunct to prolong analgesic effects, potentiates spinal anesthesia. The present study was designed to evaluate the effect of intrathecal fentanyl on the hypnotic requirements of propofol during spinal anesthesia.

METHODS: Sixty patients scheduled for elective urologic surgery under spinal anesthesia were randomly assigned to one of four groups. In Group 1 (n =15), spinal anesthesia was performed with hyperbaric bupivacaine 10 mg, in Group 2 (n = 15) with hyperbaric bupivacaine 10 mg plus fentanyl 10µgram, in Group 3 (n = 15) with hyperbaric bupivacaine 10 mg plus fentanyl 20µgram, and in Group 4 (n = 15) with hyperbaric bupivacaine 10 mg plus fentanyl 30µgram. After performing spinal anesthesia, the target plasma concentration of propofol was set at 2.0µgram/ml. Effect site concentration (Ce) was measured when the BIS's reached 80 or 70. Ce was titrated to maintain a BIS of 70-80. Observer's sedation scoring (OAA/S), systolic and diastolic pressures, SpO₂ and total infusion dose were measured every 10 minutes for 1 hour.

RESULTS: Ce's at a BIS of 80 were 1.2±0.3µgram/ml (Group 1), 1.0±0.3µgram/ml (Group 2), 0.9±0.2µgram/ml (Group 3), and 0.8±0.2µgram/ml (Group 4), respectively. Ce's at a BIS of 70 were 1.6±0.2µgram/ml (Group 1), 1.5±0.4µgram/ml (Group 2), 1.2±0.3µgram/ml (Group 3), and 1.2±0.3µgram/ml (Group 4), respectively. Ce's of Group 3 and Group 4 at BISs of 70 and 80 were significantly lower than those of Group 1 (P<0.05), and the propofol requirements of Groups 3 and 4 to maintain a BIS of 70-80 were significantly less than those of Group 1 (P<0.05).

CONCLUSIONS: These results indicate that adding more than 20µgram of fentanyl to hyperbaric bupivacaine for spinal anesthesia reduces the hypnotic requirement of propofol.