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To the Editor: Given the low frequency of SSIs in the study of Dr Pryor and colleagues,¹ we are concerned that their sample size was too small to obtain reliable results. The authors stated that 300 patients provided an 80% power to rule out a 40% difference between the treatment groups (the specified null hypothesis) at an of .05. Using an 11% infection rate in patients given 35% oxygen, as reported by Greif et al² and observed by Pryor et al, we compute that an 80% power to detect a 40% reduction in the infection rate from 11% to 6.6% would require 651 patients; 930 patients would be required to detect a 40% increase from 11% to 15.4%. The study thus appears to have been underpowered from the start—and then was stopped after only 160 patients were randomized. For a study anticipated to have 300 patients, 160 patients (53.3%) is . . . [Full Text of this Article]

Robert Greif, MD
Department of Anesthesiology and Intensive Care Medicine
Danube Hospital/SMZ East
Vienna, Austria

Daniel I. Sessler, MD
sessler@louisville.edu
Department of Anesthesiology and Pharmacology
University of Louisville
Louisville, Ky

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