Dosage of Local Anaesthetic Drug in Spinal Anaesthesia Based on Dural Sac Crosssectional Area Measured Using Ultrasound for Transurethral Resection and Inguinal Hernia Surgeries: A Double-blinded, Randomised Controlled Study

Introduction: Geriatric patients undergoing surgical procedures such as Transurethral Resection of the Prostate (TURP) and inguinal hernia repair often face an increased risk of complications due to age-related anatomical and physiological changes. The Dural Sac Cross-sectional Area (DSCSA) has been proposed as a parameter to optimise the dosage of local anesthetics in spinal anaesthesia, aiming to achieve effective sensory blockade while minimising haemodynamic instability. Aim: To determine the minimum required dose of intrathecal bupivacaine based on DSCSA for achieving a T10 sensory blockade in elderly patients undergoing TURP and inguinal hernia repair. Materials and Methods: This was a double-blinded, randomised controlled study conducted on 70 geriatric patients {American Society of Anaesthesiology (ASA) I and II} undergoing TURP or inguinal hernia repair at Dr. DY Patil Medical College and Research Centre, Pune, Maharashtra, India from July to November 2024. Patients were randomly allocated into two groups: the Control (C) group, which received a fixed dose of 10 mg hyperbaric bupivacaine, and the Ultrasound (U) group, where DSCSA was measured using ultrasound at the L3-L4 level, and the bupivacaine dosage was adjusted accordingly. Haemodynamic parameters, sensory blockade levels, motor block duration, and two-segment regression times were analysed. Data normality was assessed using the Shapiro-Wilk test, with quantitative variables compared using the independent t-test, qualitative variables analysed using the Chi-square test or Fisher’s exact test, and a p-value <0.05 considered statistically significant. Results: Baseline characteristics such as age, height, weight, ASA grade, and surgery duration were comparable between groups (p>0.05). The mean DSCSA in the U group was 120.03±12 mm2 , with a calculated mean dose of 7.99±0.77 mg bupivacaine, significantly lower than the fixed 10 mg in the C group (p<0.0001). The highest sensory level reached was T8 in the U group and T4 in the C group (p=0.004). The U group had a significantly shorter motor block duration (157.23±11.92 min vs. 199±21.86 min, p<0.0001) and two-segment regression time (52.5±13.44 min vs. 62.64±14.49 min, p=0.003). The C group experienced a greater decrease in Mean Arterial Pressure (MAP) (p<0.0001) with a higher need for vasopressor support. Conclusion: Tailoring the intrathecal bupivacaine dosage based on DSCSA significantly reduces the risk of excessive cephalad spread, minimising haemodynamic fluctuations while maintaining adequate anaesthesia. Ultrasound-guided DSCSA measurement can serve as a valuable tool for optimising spinal anaesthesia in geriatric patients.