EFFECT OF INTRATHECAL FENTANYL ON ALERTNESS

Spinal anaesthesia using a local anaesthetic with fentanyl has been reported to induce sedation. The present study was designed to evaluate the effect of intrathecal fentanyl on alertness level in unsedated patients undergoing lower limbs orthopedic surgery by using the Modified Observer’s Assessment of Alertness/Sedation (MOAA/S) scores and Bispectral Index (BIS) monitoring. Patients and Methods: Sixty patients scheduled for elective orthopedic surgery under spinal anaesthesia were randomly allocated into two groups to receive either fentanyl 25 mcg (n = 30) or normal saline (n = 30) with hyperbaric bupivacaine 12.5 mg for subarachnoid block. Baseline mean arterial pressure (MAP), bispectral index (BIS) value, Modified Observer’s Assessment of Alertness/Sedation (MOAA/S) score and other routine monitoring were assessed before and every 5 min for 90 min after initiation of spinal anaesthesia. The level of sensory block was evaluated at 5, 10, 20, and 30 minutes after subarachnoid drug administration and the degree of patient’s satisfaction had been assessed at the end of study. Results: The mean BIS value and MOAA/S score taken across all assessment time points during study period in the fentanyl group (91.34±2.81 and 4.04±0.30) were significantly lower than those of the control group (95.91±1.37 4.90±0.31) (P = 0.000). Both BIS values and MOAA/S scores decreased progressively from the baseline in the fentanyl group, this decrease was significant from 30 to 65 min for BIS and from 20 to 80 min for MOAA/S after completion of spinal anaesthesia. The decrease in arterial blood pressure was 20% with no significant difference between both groups. The mean height of sensory block at 30 min was Th 8.9±2.3 in control group versus Th 8.1±2.1 in fentanyl group (P = 0.165). Conclusion: The combination of bupivacaine and fentanyl for spinal anaesthesia produces a more consistent sedative effect and higher reduction in alertness level than single bupivacaine as measured by BIS index and OAA/S.