Effect of the Dialysis Membrane in Acute Renal Failure

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Abstract
We found the study by Hakim et al. (Nov. 17 issue)1 comparing biocompatible and bioincompatible dialysis membranes for the treatment of acute renal failure interesting but flawed in several respects. The improvement in survival in the patients without oliguria can only be considered to be due to differences in the membrane used for dialysis if the original patients were evenly randomized according to their risk of death, a presumption that the authors attempted to support on the basis of the similarity of the raw Acute Physiology, Age, and Chronic Health Evaluation (APACHE II) scores. The APACHE II score, however, is only one factor in an exponential equation that must be used to determine the risk of death.2 Also included in this equation is a diagnostic-category weight. Thus, if the main diagnostic category was renal, patients with an APACHE II score of 29 would have an expected mortality rate of 46 percent, but if the diagnostic category was gastrointestinal, the expected mortality rate would be 77 percent.