Patients who consent to receive spinal anesthesia (as opposed to some other anesthetic technique) and who meet the inclusion/exclusion criteria for the study (given below) will be randomized on day of surgery after obtaining informed consent to either ultrasound-guided or standard spinal anesthesia technique.
A block randomization scheme with random block sizes ranging from 2-8 patients will be used. The outcomes will be recorded by a third party observer in the block room/operating room who might be a nurse or resident or clinical research fellow not directly involved with performing the block. The post procedure outcomes will also be recorded by a clinical research fellow or resident who was not directly involved with performing the block.
No sample size estimation methodology currently exists for the right-censored count data models. We expect less number of attempts in the ultrasound group a 20 % difference between the two groups which we feel is a minimum of a clinically-relevant effect. At the 0.05 level of significance with a power of 0.8, we will require a minimum of 20 patients per group,therefore we plan to recruit 40 patients in total.
The analysis will be conducted by a statistician who will be blinded.
