Sample size calculation
TBI, VFD
Our sample size was calculated based on our primary outcome of ventilator-free days (VFD) after adrenergic blockade in severe TBI patients. As this was a pilot study that is the first of its kind, we utilized a clinically relevant difference between the experimental and control mean VFD of 2 days, with a standard deviation of 3 days; we calculated that 48 experimental and 48 control subjects were required to achieve 90% power, plus accounting for 4 patient withdrawals. A planned interim analysis (described in detail in our “Interim Analysis Plan”) accounts for the uncertainty in the true difference in VFD [