Ultrasound-guided measurement of cross-sectional area of dural sac to titrate the dosage of local anaesthetic in geriatric orthopaedic surgery under spinal anaesthesia: A prospective randomised study.

BACKGROUND AND AIMS: Dural sac cross-sectional area (DSCSA)-based intrathecal dosing aims to optimise block spread and improve haemodynamic stability during spinal anaesthesia (SA). Ultrasound-guided DSCSA measurement helps in local anaesthetic (LA) dose reduction compared with conventional fixed-dose practice. The primary objective was to determine LA dosage proportional to DSCSA reduction, while the secondary objectives included comparison of block characteristics and intra-operative haemodynamic parameters [heart rate and mean arterial pressure (HR and MAP)] between the two approaches.

METHODS

This prospective randomised study included 60 American Society of Anesthesiologists I-III patients aged >65 years undergoing orthopaedic surgery under SA. Patients were allocated to an ultrasound-guided DSCSA-based dosing group (US, n = 30) or a control group (C, n = 30). In Group US, DSCSA was calculated from ultrasound-measured dural sac diameter at L3-L4, and hyperbaric bupivacaine dosing was individualised, while Group C received a fixed 11 mg dose. Sensory and motor block characteristics, HR, MAP, and surgical duration were recorded.

RESULTS

Group US had a mean dural sac diameter of 11.99 (0.76) mm and a DSCSA of 112.98 (13.42) mm², resulting in a mean calculated dose of 1.79 (0.14) mL. Both groups achieved a maximum motor block score of 3. Group C showed significantly greater reductions in HR, with more frequent bradycardia, and a significant decrease in MAP between 10 and 30 minutes. Surgical duration was comparable between the groups.

CONCLUSION

Ultrasound-guided DSCSA-based dosing improves haemodynamic stability and reduces bradycardia and hypotension while maintaining comparable block quality to conventional fixed-dose SA.