Comparison of the effects of isobaric and hyperbaric bupivacaine on block characteristics, maternal hemodynamic profiles, postoperative pain score and time to first analgesic request following spinal anesthesia for elective cesarean section: A Multicenter Prospective Cohort Study

Background Cesarean section is one of the most common surgical procedures performed worldwide and is frequently conducted under spinal anesthesia. The baricity of bupivacaine being isobaric or hyperbaric plays a critical role in determining its spread within the cerebrospinal fluid, thereby influencing the onset and level of sensory and motor blockade, maternal hemodynamic stability, and duration of postoperative analgesia. This study aimed to provide further evidence on this clinically important topic. Objective To compare the effects of isobaric versus hyperbaric bupivacaine on block characteristics, maternal hemodynamic profiles, postoperative pain scores, and time to first analgesic request following spinal anesthesia for elective cesarean section at selected public hospitals in Addis Ababa, Ethiopia, 2026. Methods A total of 64 eligible parturients who were scheduled for elective cesarean section under spinal anesthesia were included in two groups (n = 32 each). Both the isobaric and hyperbaric groups received 10–12.5 mg of bupivacaine. Data were collected via a pretested structured data collection tool and entered with EpiData 3.1 and analyzed via STATA version 17. Normality was checked with the Shapiro-wilk test. Descriptive statistics, independent t tests, Mann–Whitney U test, ordinal logistic regression, linear mixed-effects models, and Kaplan-Meier analysis were employed as appropriate. A p-value of < 0.05 was considered statistical significance. Results Hyperbaric bupivacaine provided significantly faster onset of sensory block to T6 (median 5 vs. 8 minutes) and faster achievement of complete motor block. It was also associated with higher sensory block levels and superior hemodynamic stability, as evidenced by smaller reductions in systolic, diastolic, and mean arterial pressure, particularly between 5 to 20 minutes after injection. In contrast, at 3 and 4 hours, the hyperbaric group had statistically significant with higher VAS scores than did the isobaric group (3 hour: β = 2.53, 95% CI: 1.43 to 3.63, p < 0.001; 4 hour: β = 2.91, 95% CI: 1.81 to 4.01, p < 0.001). Isobaric bupivacaine had longer time to first analgesic request (median 4.5–5 hours versus 3–4 hours, log-rank p < 0.001). Conclusion Hyperbaric bupivacaine offers faster onset, higher block level, and better hemodynamic stability, whereas isobaric bupivacaine provides prolonged postoperative analgesia.