Polymyxin B Hemoperfusion and Mortality in Abdominal Septic Shock

To the Editor: In their randomized controlled trial, Dr Cruz and colleagues¹ reported that polymyxin B hemoperfusion reduced 28-day mortality in patients with severe sepsis or septic shock. I believe that this conclusion is wrong. The statistically significant difference in mortality rates reported in this study was based on the analysis of a hazard ratio generated by a Cox proportional hazards regression survival model. However, the odds ratio (OR) of the crude 28-day mortality rates did not reach statistical significance (11/34 vs 16/30; OR, 0.42; 95% confidence interval [CI], 0.13-1.29; P = .13). Such a difference between the hazard ratio and the OR can only be explained by a later occurrence of deaths in the treated group, an effect that is suggested in Figure 3.¹ This observation is concerning in an unblinded trial, in which investigators could forgo life support later in patients in the treatment group, creating a false appearance of improved survival in that group early in the study. It would therefore be helpful to know the mortality rates at 60 or 90 days; the narrowing difference between mortality rates that seems to be occurring over 28 days in Figure 3 may have decreased further over longer periods.