Intrathecal Midazolam Versus Fentanyl as Adjuvants To Hyperbaric Levobupivacaine 0.5% For Subarachnoid Block in Elective Caesarean Section: A Randomized Double-Blind Comparative Study

Abstract

Background: Subarachnoid block is the preferred technique for elective caesarean section, but a single-shot intrathecal local anaesthetic has a finite duration of action. Intrathecal adjuvants such as fentanyl and midazolam are used to prolong analgesia; however, direct comparisons of the two when combined with hyperbaric 0.5% levobupivacaine remain limited.

Objectives: To compare the onset and duration of sensory and motor blockade, perioperative hemodynamic stability, duration of postoperative analgesia, and adverse effects of intrathecal midazolam versus fentanyl, each added to hyperbaric 0.5% levobupivacaine, in women undergoing elective caesarean section.

Methods: In this prospective, randomized, double-blind study, 64 ASA physical status II women aged 18–35 years scheduled for elective lower-segment caesarean section were randomly allocated to receive either hyperbaric levobupivacaine 0.5% 2 mL (10 mg) with fentanyl 25 µg (Group LF, n = 32) or hyperbaric levobupivacaine 0.5% 2 mL (10 mg) with midazolam 2 mg (Group LM, n = 32) intrathecally. Onset and duration of sensory and motor block, time to two-segment regression, time to first rescue analgesia, intraoperative hemodynamic parameters, and adverse effects were recorded by a blinded observer and analysed using an independent-samples t-test and chi-square/Fisher exact test, with p < 0.05 taken as significant.

Results: The two groups were comparable for age, anthropometric measures, baseline vitals and ASA status. Onset of sensory blockade (3.68 ± 0.79 vs 3.49 ± 0.98 min, p = 0.41) and onset of motor blockade (4.72 ± 1.24 vs 4.58 ± 1.35 min, p = 0.39) were similar between Group LF and Group LM, as was the maximum sensory level achieved (T4 in 71.9% vs 68.8%, p = 0.784). Duration of sensory blockade was significantly longer in Group LM (211.54 ± 24.84 min) than Group LF (196.95 ± 27.26 min, p = 0.028), as was time to two-segment regression (162.83 ± 31.90 vs 147.33 ± 29.60 min, p = 0.047). Time to first rescue analgesia was significantly prolonged in Group LM (211.54 ± 24.84 min) compared with Group LF (196.95 ± 27.26 min, p = 0.028). Heart rate, systolic and mean arterial pressures were comparable throughout surgery, and adverse effects (nausea, vomiting, pruritus) were infrequent and statistically similar between groups (p = 0.295).

Conclusion: When combined with hyperbaric 0.5% levobupivacaine for elective caesarean section, intrathecal midazolam produced sensory and motor block onset comparable to fentanyl, with preserved hemodynamic stability, but conferred a significantly longer duration of sensory blockade and postoperative analgesia without an increase in adverse effects. Intrathecal midazolam may therefore be considered a favourable opioid-sparing alternative to fentanyl in this setting.