Relation between fentanyl dose and level of consciousness measured with patient state index during spinal anesthesia for elective cesarean section　　

Background
The addition of opioid to a local anesthetic solution for spinal anesthesia is known to exhibit sedative effect. However, this effect has not been adequately studied during cesarean section. It has been reported that PSI value was approximately 80 that was similar to a score of 4 on the Observer’s Assessment of Alertness and Sedation system [1].The purpose of the present study was to examine the relationship between fentanyl dose and sedative effect using patient state index (PSI) value. 

Methods
After IRB approval, 15 patients scheduled to undergo cesarean section with combined spinal and epidural anesthesia were involved. Patients were divided into three groups, with each group receiving a different dose of fentanyl (10 µg, 15 µg, and 20 µg).An epidural catheter was inserted into Th12 / L1. 3 ml of 1% xylocaine was administered as a test drug, without any further drug administration during surgery. Spinal anesthesia with 2.2 ml of hyperbaric bupivacaine combined with the appropriate dose of fentanyl was administered at L3 / 4. Following injection, oxygen (5 L/min) was administered through a mask. Patients were monitored for Respiratory Rate (RR), SpO2, and PSI values with Root® with SedLine®(Masimo Corp., Irvine CA) .We calculated the average of cumulative time and ratio of the time that had been PSI < 90 and PSI < 80 from delivery to the end of surgery. RR < 8 breaths/min or SpO2 < 95% was defined as respiratory depression. Data were analyzed using one-way ANOVA with a significance level set at p < 0.05.

Results 
There were no significant differences among the three groups in terms of age, height, body weight, ASA classification, surgical time, and block level. Cumulative time and ratio of the time in the three groups for patients with PSI < 90 were 2.8 min, 14.4 min, and 36.8 min (p = 0.008) and 6.9%, 30.1%, and 71.0% (p = 0.003), while patients with PSI < 80 were 0 min, 4 min, and 14 min (p = 0.272) and 0%, 9.7%, and 24.6% (p = 0.287) respectively. Respiratory depression was not observed in any patient. 

Conclusion
As increase dose of fentanyl from 10µg to 20µg, the time of PSI<80 was increased. Respiratory depression was not observed in all groups. 

Reference
[1] Drover et al. Best Practice & Research Clinical Anaesthesiology vol.20, No.1, pp.121-128, 2006