The minimal effective dose of spinal hyperbaric bupivacaine for successful reliable saddle block for minor perianal surgeries

Objective The aim of this study was to determine the minimal effective dose of spinal hyperbaric bupivacaine required to induce a reliable and satisfactory saddle block for perianal surgeries (using a modified Dixon’s up-and-down method). Materials and methods A total of 24 adult patients scheduled for perianal surgeries were enrolled in this study. Dural puncture was performed using a standard midline approach in the sitting position at the L3–L4 intervertebral space, using a 25 G Whitacre needle with its orifice directed caudal. A small quantity (1.5 mg) of hyperbaric bupivacaine was injected. All patients remained in the sitting position for 10 min immediately before and after surgery; the block was tested using a long surgical toothless clamp and modified Bromage scale. A successful block was defined as one that was sufficient to proceed with the surgery without any supplementation. The dose of bupivacaine given to the next patient was guided by modified Dixon’s up-and-down method using 0.5 mg as a step size. Patients’ ability to position themselves, ambulation time, time of hospital discharge, patient and surgeon satisfaction, and any intraoperative or postoperative complication were recorded. The minimal effective dose of hyperbaric bupivacaine for successful saddle block for 50% ( ED50) of patients was determined by calculating the midpoint dose of all independent pairs of patients after at least seven crossover points. Results The ED50 of hyperbaric bupivacaine for successful saddle block for perianal surgeries was 1.9 mg (95% confidence interval = 1.7–2.1 mg). There were zero motor blockade, early ambulation, short time to void, and early hospital discharge, as well as no complications and excellent patient and surgeon satisfaction. Conclusion The ED50 of spinal hyperbaric bupivacaine for saddle block for perianal surgery is 1.9 mg (95% confidence interval = 1.7–2.1 mg). This block is reliable and has short duration, no complication, and excellent patient and surgeon satisfaction.