The Effect of Body Mass Index on Vasopressor Use, Block Dynamics, and Hemodynamic Responses in Urological Surgery Undergoing Spinal Anesthesia

Background While the effects of body mass index (BMI) on intrathecal local anesthetic spread and hemodynamic responses during spinal anesthesia are well-defined in obstetric surgery, studies directly examining this relationship in urological surgeries where spinal anesthesia is commonly performed are limited. Therefore, this study aimed to evaluate the effect of BMI on vasopressor requirements and block characteristics after spinal anesthesia. Methods This prospective, observational study included 120 patients undergoing elective urological surgery under spinal anesthesia. Patients were divided into two groups according to BMI: BMI < 27.5 kg/m² (Group L) and BMI ≥ 27.5 kg/m² (Group H). The groups were compared in terms of demographic data, surgical duration, spinal block characteristics, hemodynamic changes, and ephedrine use. Results Three patients were excluded from the analysis due to spinal anesthesia failure, and a total of 117 patients were evaluated (Group L: n = 60; Group H: n = 57). Total intraoperative ephedrine requirement was significantly higher in Group H (p < 0.001). The maximum sensory block level was significantly more cephalic in Group H compared to Group L (T7.42 ± 2.63 vs T8.97 ± 1.99, p < 0.001). No significant differences were found between the groups in terms of time to reach maximum block, time to two-segment sensory block regression, time to reach motor block 3, and motor block recovery time (p > 0.05). Although basal systolic arterial pressure was higher in Group H (p = 0.019), hemodynamic parameters after spinal anesthesia were similar between the groups. Conclusions In the high BMI patient group, a significant effect was observed on vasopressor requirement, block level, and surgical duration during spinal anesthesia procedures. These findings highlight the need for comprehensive preoperative planning, determination of appropriate anesthesia strategies, and careful hemodynamic monitoring in obese patients.