Dural sac cross-sectional area measured using ultrasound to modify the dosage of local anaesthetic in spinal anaesthesia for transurethral resection of prostate surgery: A prospective, double blind, randomised controlled study

Background and Aims: The area of lumbar spinal canal decreases with age, and hence the level of sensory blockade is higher in the elderly after spinal injection. The present study optimised the dose of local anaesthetic in elderly patients based on the lumbar dural sac cross sectional area (DSCSA) determined using ultrasound. Methods: Sixty patients of age above 60 years undergoing transurethral resection of prostrate (TURP) surgery in a tertiary care hospital were included in the study. Patients were categorised into two groups of 30 each based on a computer-generated random number table. In the control group (C), 2 ml of 0.5% hyperbaric bupivacaine was given and in the ultrasound group (U), the drug dose was modified according to DSCSA which was measured using the formula area = pi (diameter/2)(2). Results: The DSCSA and bupivacaine dosage were significantly lower in group U compared to control group (P = 0.0001). The maximal level of cephalad spread of sensory blockade was significantly lower in ultrasound group, than in control group (P = 0.002). The two-segment block regression time and motor recovery time was less in group U. Higher mean arterial pressure (105.8 +/- 9.66 mmHg; P = 0.007), and a lower decrease from baseline (14.15 +/- 7.55%; P = 0.041) was noted in group U after subarachnoid block. Conclusion: The estimation of DSCSA is an effective parameter and can be used to modify the dose of local anaesthetic for subarachnoid block in elderly patients undergoing TURP surgery.