A Real-Time Ultrasound Guided Approach For Spinal Anesthesia

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. 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.
The analysis will be conducted by a statistician who will be blinded.