Sonographic assessment of predictors of depth of the corner pocket for ultrasound-guided supraclavicular brachial plexus block.

Background and Aims: There is wide variation in depth of brachial plexus in patient population at supraclavicular region. We plan to find the depth of the corner pocket and correlate it with age, weight, height and body mass index (BMI). Material and Methods: After approval from Ethics Committee, right-sided supraclavicular region of volunteers was scanned. Once an optimal image, which included subclavian artery, pleura, first rib and nerve bundles, was obtained, the corner pocket was kept in the middle of the screen and the image was frozen. Depth of the corner pocket from the skin was measured. Thereafter longest distance (LD) approximating needle trajectory was calculated. The Pearson correlation was used to calculate the relation between these two distances and various predictors such as weight, height, and BMI. Results: Mean shortest distance that is, vertical distance from skin to corner pocket for all volunteers was found to be 1.7 ± 0.8 cm and the mean LD that is, distance traveled by needle entering 1 cm from the edge of foot process to the corner pocket in an in-plane approach was 3.7 ± 0.2 cm. We did not find any significant correlation between age, height versus measured distances. However, significant correlation (0.11) was found between weights, BMI versus two lengths. Conclusion: Prescanning of supraclavicular region for estimating depth of corner pocket should be done before choosing an appropriate size needle. Furthermore, the needle should not be advanced more than the predicted corner pocket depth.