Effects of different positions on sensory and motor blockade in patients undergoing anorectal surgery under spinal anesthesia

Background and objectives Benign anorectal diseases are prevalent in the general population. Currently, spinal anesthesia is mainly performed in the lateral and sitting positions and is rarely performed in the prone or jackknife positions. This study compared the effects of the prone, lateral, and sitting positions on sensory and motor blocks in patients undergoing anorectal surgery under spinal anesthesia. Materials and methods In this prospective comparative study, 75 ASA I and II class patients aged >18 years who underwent anorectal surgery were included, with 25 patients in each group. Spinal anesthesia was administered at the L3–L4 or L4–L5 intervertebral space using a No. 25 Quincke needle and 10 mg of 0.5% hyperbaric bupivacaine in the prone, lateral, or sitting position. Outcomes related to sensory and motor blocks and the anesthesia success rate were compared among the three groups. Results Sensory block reached T10 in most patients in the prone (44%) and lateral (52%) groups, compared with L1 in the sitting group (56%; p = 0.004). Motor block depth (Bromage 3) was observed in 44% (prone), 48% (lateral), and 84% (sitting) of patients (p = 0.04). Sensory block onset was slower in the prone (2.92 ± 0.87 min) and lateral (2.72 ± 0.87 min) vs. sitting (1.94 ± 1.92 min; p = 0.001). Sensory block duration was longer in the prone (79.96 ± 14.42 min) and lateral (80.28 ± 16.55 min) vs. sitting (67.64 ± 15.99 min; p = 0.007). Motor block duration was shorter in the prone (75.64 ± 12.59 min) and lateral (74.12 ± 14.20 min) vs. sitting (87.30 ± 18.24 min; p = 0.005). Hemodynamic stability was better in the prone and lateral positions (p = 0.0001). First-attempt success was higher in the sitting group (76%) vs. prone (36%) and lateral (68%) positions (p = 0.009). Conclusion The prone and lateral positions provide higher sensory block levels and better hemodynamic stability, whereas the sitting position is associated with faster sensory block onset, deeper motor block, and higher first-attempt success. The choice of position should be individualized according to surgical requirements and patient characteristics.