Uerpairojkit K, Srituravanich W, Songthamwat B, Kampitak W, Nantapak T, Kharuram P. Prospective randomized study of preprocedural ultrasound scan for spinal anesthesia 1 comparison between using 2nd prototype of PASS and skin marking technique to locate needle entry point. Thai J Anesthesiol [internet]. 2022 Jan. 26 [cited 2026 Oct. 1];48(1):1-8. available from: https://he02.tci-thaijo.org/index.php/anesthai/article/view/255816