The addition of fentanyl does not alter the extent of spread of intrathecal isobaric bupivacaine in clinical practice

PurposeFentanyl is commonly added to intrathecal local anesthetic solutions. In vitro data has shown fentanyl to render isobaric local anesthetics hypobaric, and alter the spread in artificial cerebrospinal fluid. This study examined whether the addition of fentanyl to isobaric bupivacaine with morphine leads to a clinically important alteration in the extent of spread of anesthesia.MethodsForty-four ASA I-III patients undergoing lower limb orthopedic procedures completed this double-blind, placebo-controlled trial. Patients were randomized into one of two groups, receiving intrathecal bupivacaine 15 mg and preservative-free morphine 200 μg without (Control group), or with the addition of fentanyl 0.02 mg (Fentanyl group). Patients were maintained at a slight head-up tilt. Variables studied over three hours included sensory level to cold and pinprick, motor blockade (Bromage scale), and circulatory data.ResultsNo differences existed between the Fentanyl and Control groups with respect to highest level of block for cold: T4 (T2–T5) vs T3.5 (T3–T8) respectively (median, 95% confidence interval) or pinprick: T4 (T3–T6) vs T4.5 (T3–T8). Similarly, there was no difference in the time taken to reach maximum block height to cold (20 ± 9 vs 23 ± 13 min, mean ± SD) or pinprick (20 ± 9 vs 24 ± 13 min).ConclusionThe addition of fentanyl 0.02 mg to 0.5% bupivacaine with morphine does not affect the maximal block height or time to maximal block in clinical practice.