Sample size and power calculations Tracheal tube cuff pressures are typically inflated to a pressure ranging from 20 to 25 cm H2O, with tracheal mucosal injury occurring at cuff pressures exceeding 30 cm H2O. Based on estimate of anticipated true difference in the means of cuff pressures on land and in flight of 12 and estimate of standard deviations of cuff pressure distributions, we will need to study 60 experimental subjects and 60 control subjects to be able to reject the null hypothesis that the mean change in cuff pressure of the experimental and control groups are equal with probability (power) 0.9. The type I error probability associated with this test of this null hypothesis is 0.05.