Sample size
congential heart disease
The weight-based loading protocol was designed to achieve a 25(OH)D concentration of > 75 nmol/L in 75% of study participants in the intervention arm, with a minimal acceptable proportion of 50% achieving this target. Assuming the true proportion achieving target was 75%, a random sampling of 36 patients would have ~ 90% power to return an estimate in excess of 66% of participants achieving target 25(OH)D. Given an estimate in excess of 66% and a sample size of 36, the lower 95% confidence interval would exclude 50%. To account for an anticipated 5% drop out rate or missing blood samples, we aimed to recruit a total sample size of 60 patients: 40 patients into the high dose arm, and 20 in the placebo arm. Although a control group was not relevant for the primary outcome (evaluating response to vitamin D loading dose), it was determined to be essential for evaluating abnormalities in blood or urine calcium levels. Of these two, urine calcium levels are infrequently measured in the ICU, and having a control group would be essential to interpreting the levels. For example, our pilot randomized controlled trial of pre-operative vitamin D supplementation in stable congential heart disease demonstrated that 17% of patients have elevated urine calcium peri-operatively [