 Demonstrating that non-blocked patients analgesic requirements differ from the hypothesized mean for blocked patients at α0.05 and 80 power will require a total sample size of 16 8group. This estimate is based on observational data for non-blocked patients from our own practice, and our estimate of the minimum clinically-significant difference in analgesic requirements to be expected in blocked patients. We currently estimate that enrollment of 20 participants should be sufficient to accumulate 16 who complete the protocol , and will apply to HRRC for an amendment to enroll more should that be necessary. 