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

Purpose: Fentanyl is commonly added to intrathecal local anesthetic solutio ns. In vitro data has shown fentanyl to render isobaric local anesthetics h ypobaric, and alter the spread in artificial cerebrospinal fluid. This stud y examined whether the addition of fentanyl to isobaric bupivacaine with mo rphine leads to a clinically important alteration in the extent of spread o f anesthesia. Methods: Forty-four ASA I-III patients undergoing lower limb orthopedic pro cedures completed this double-blind, placebo-controlled trial. Patients wer e randomized into one of two groups, receiving intrathecal bulpivacaine 15 mg and preservative-free morphine 200 mug 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 sens ory level to cold and pinprick, motor blockade (Bromage scale), and circula tory data. Results: No differences existed between the Fentanyl and Control groups wit h respect to highest level of block for cold: T4 (T2-T5) vs T3.5 (T3-T8) re spectively (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 ma ximum block height to cold (20 +/- 9 vs 23 +/- 13 min, mean +/- SD) or pinp rick (20 +/- 9 vs 24 +/- 13 min). Conclusion: The addition of fentanyl 0.02 mg to 0.5% bupivacaine with morph ine does not affect the maximal block height or time to maximal block in cl inical practice.