Relation between fentanyl dose and patient state index during spinal anesthesia for elective cesarean section

Background: In spinal anesthesia for cesarean section, the addition of fentanyl to the local anesthetic has been reported to improve perioperative analgesia. However, there is only limited knowledge on sedative effects of the added fentanyl. We examined whether the patient state index (R) (PSI) can detect and present the light sedated level with patients undergoing cesarean section. Findings: We measured respiratory rate (RR), SpO2, and PSI values. Between child delivery and the completion of the operation, the proportions of time with the PSI values < 90 and 80 were calculated. RR <8 breaths/min or SpO2 <95 % was defined as respiratory depression. Respiratory depression was not observed in any patient. At fentanyl doses of 10, 15, and 20 mu g, the proportions of time with the PSI < 90 were 14.5 +/- 20.8, 49.4 +/- 35.3, and 71.1 +/- 22.9 %, respectively (P < 0.01). There were significant differences between 10 and 15 mu g (P < 0.05), and 10 and 20 mu g (P < 0.01). Similarly, the proportions of time with the PSI values < 80 were 0.5 +/- 1.8, 21.1 +/- 24.1, and 31.8 +/- 32.2 %, respectively (P < 0.05). There was a significant difference between 10 and 20 mu g (P < 0.05). Conclusions: The PSI values decreased in a dose-dependent manner with increasing dose of fentanyl, but no respiratory depression was observed. The PSI values decreased to less than 90, when fentanyl was administered more than 15 mu g. Furthermore, the PSI values decreased to less than 80, when fentanyl was administered 20 mu g.