Sample size considerations
pain
48 h post-operative coughing on the NRS scores was defined as a clinically meaningful effect. Assuming a standard deviation of 2 for each of the three pain score outcomes on the basis of a preliminary study. The pretest result was an NRS score of 1.3 for group M, 1.2 for group B and 3.3 for group C at 48 h postoperative coughing. A sample size of 20 patients per group had 90% power to detect effectiveness of intrathecal morphine and intravenous analgesic pumps on all three primary outcomes at the 0.05 significance level. To allow for some individuals not completing the trial, 33 patients were recruited in each treatment group.