To the Editor: In their randomized controlled trial, Dr Cruz and colleagues1 assessed the early use of polymyxin B hemoperfusion in abdominal sepsis. I am concerned that the investigators may have confused the analysis of time until death with mortality at 28 days.
Survival analysis, presented in the article as the hazard ratio, estimates the relative rate of events in the 2 groups testing a hypothesis that hemoperfusion prolongs time until death. From the article, it might appear that there was a statistically significant difference between the 53% mortality in the control group and the 32% mortality in the treated patients at 28 days, or that the number needed to treat was 4.8 septic patients with hemoperfusion to save 1 life. Neither conclusion would be justified from the data.
Amaral ACKB. Polymyxin B Hemoperfusion and Mortality in Abdominal Septic Shock. JAMA. 2009;302(18):1968-1970. doi:10.1001/jama.2009.1607