The effect of intrathecal fentanyl on Cerebral State Index-guided sedation during spinal anaesthesia

Comparison of subarachnoid block with bupivacaine and bupivacaine with fentanyl on entropy and sedation: A prospective randomized double-blind study

BACKGROUND AND AIMS

We studied the state entropy to monitor the sedative effect of subarachnoid block (SAB) using bupivacaine alone or combination of bupivacaine and fentanyl. The effect of use of fentanyl via the subarachnoid route on the sedation level was also studied using the entropy scores and the decrease in the requirement of propofol used as an adjuvant sedative drug.

MATERIALS AND METHODS

In this prospective randomized double-blind study, 30 patients of age 18-70 years requiring SAB were enrolled for the study. Patients with any known allergy to study drugs, contraindication for SAB, obesity, neurological or psychiatric disease on concurrent medication and refusal were excluded from the study. Patients were randomly allocated into two groups: Group C: SAB was administered with 2.5 mL (12.5 mg) of 0.5% hyperbaric bupivacaine; Group D: SAB was administered with 2.5 mL of 2 mL (10 mg) of 0.5% hyperbaric bupivacaine and 0.5 mL (25 μg) fentanyl. Propofol infusion was started if the state entropy (SE) value was ≥75, at the rate of 100 μg/kg/min till the SE value reaches in the range of 60-75 (recorded as onset time). Thereafter the infusion rate was titrated to maintain SE value between 60 and 75. The level of sedation was measured with SE and Ramsay sedation (RS) scale.

RESULTS

The demographic profile and baseline parameters, were comparable in two groups (P > 0.05). After SAB, decrease in SE and response entropy was noted in both the groups and fall was significant in Group D (P < 0.0001). The total propfol required in thew two groups were comparable being 3.97 ± 2.14 mg/kg in Group C and 3.41 ± 2.34 mg/kg in Group D (P = 0.342). The change in the mean RS values was from 1.17 ± 0.38 to 1.69 ± 0.47 in Group D (P = 0.06), whereas in Group C it was from 1.03 ± 0.18 to 1.43 ± 0.50 (P = 0.041) within 20 min of SAB.

CONCLUSION

Subarachnoid block causes sedation per se, but the level of sedation is not clinically significant and the sedation caused is not enough to avoid sedative agents for allaying anxiety in patients intraoperatively. The sedative effect of SAB was enhanced by adding intrathecal fentanyl probably because of better quality of SAB. SE showed good correlation with RS scaling system. Therefore, SE may be used as reliable tool to titrate sedation in patients undergoing surgery under SAB.

Intrathecal fentanyl decreases the optimal effect site concentration of propofol during spinal anaesthesia

BACKGROUND

The aim of this study was to assess the possible difference in the optimal effect site concentration of propofol for conscious sedation during spinal anaesthesia with or without intrathecal fentanyl in patients undergoing urologic surgery. The hypothesis was that intrathecal fentanyl would decrease the effect site concentration of propofol needed for conscious sedation.

METHODS

Among 43 patients, 23 patients received fentanyl 25 mcg and 20 patients received normal saline in addition to hyperbaric bupivacaine 10 mg during spinal anaesthesia. Propofol was infused at a dose determined by a modified Dixon's up-and-down method. The Cerebral State Index was recorded once target effect site concentration was reached to determine the effect of the successfulness of the conscious sedation.

RESULTS

The half maximal effective concentration (EC50) of the effect-site concentration of propofol for sedation was 1.67 ± 0.28 mcg/ml in the control group and 0.87 ± 0.15 mcg/ml in the fentanyl group (P = 0.02). The propofol dose for conscious sedation during spinal anaesthesia was decreased by 48% when intrathecal fentanyl 25 mcg was added to local anaesthetics.

CONCLUSION

The EC50 of the effect-site concentration of propofol for sedation decreased from 1.67 ± 0.28 mcg/ml to 0.87 ± 0.15 mcg/ml with the addition of 25 mcg fentanyl to a spinal anaesthetic in patients undergoing urologic surgery.