Tumor necrosis factor clearances during veno-venous hemodiafiltration in the critically ill.

Tumor necrosis factor alpha (TNF) is a mediator of injury in the critically ill. Its small molecular size (17 kd) should allow its clearance during continuous hemodiafiltration (CHD). The authors studied TNF extraction in 12 critically ill patients (APACHE II score 26.3 mean; range, 19-34) receiving CHD. Tumor necrosis factor levels were measured in prefiltered and filtered blood and ultradiafiltrate at 0.4 and 24 hours of therapy. Before CHD, mean plasma TNF levels were 261 pg/ml (95% confidence interval [CI]: 184-578) and 291 pg/ml (95% CI: 0-589) after 24 hours. There were no statistically significant differences between prefilter and postfilter TNF levels. Most ultradiafiltrate samples (74%) contained demonstrable TNF (mean, 314 pg/ml; 95% CI: 67-561). Daily TNF excretion was a mean of 15.9 micrograms (+5.6 standard error [SE]), with a mean daily clearance of 27.5 L (95% CI: 2.5-52.5). The authors conclude that significant amounts of TNF are excreted in the ultradiafiltrate during CHD. This observation may provide a rationale for use of similar therapies in critically ill patients in the absence of conventional indications for dialytic support.