Early net ultrafiltration rate and mortality in critically ill patients receiving continuous renal replacement therapy

Background. In patients treated with continuous renal replacement therapy (CRRT), early net ultrafiltration (NUF) rates may be associated with differential outcomes. We tested whether higher early NUF rates are associated with increased mortality in CRRT patients. Methods. We performed a retrospective, observational study of all patients treated with CRRT within 14 days of intensive care unit admission. We defined the early (first 48 h) NUF rate as the volume of fluid removed per hour adjusted for patient body weight and analysed as a categorical variable (>1.75, 1.01-1.75 and <1.01 mL/kg/h). The primary outcome was 28-day mortality. To deal with competing risk, we also compared different time epochs. Results. We studied 347 patients {median age 64 [interquartile range (IQR) 53-71] years and Acute Physiology and Chronic Health Evaluation III score 73 [IQR 54-90]}. Compared with NUF rates <1.01 mL/kg/h, NUF rates >1.75 mL/kg/h were associated with greater mortality rates in each epoch: Days 0-5, adjusted hazard ratio (aHR) 1.27 [95% confidence interval (CI) 1.21-1.33]; Days 6-10, aHR 1.62 (95% CI 1.55-1.68); Days 11-15, aHR 1.87 (95% CI 1.79-1.94); Days 16-26, aHR 1.92 (95% CI 1.84-2.01) and Days 27-28, aHR 4.18 (95% CI 3.98-4.40). For every 0.5 mL/kg/h NUF rate increase, mortality similarly increased during these epochs. Conclusion. Compared with early NUF rates <1.01 mL/kg/h, NUF rates >1.75mL/kg/h are associated with increased mortality. These observations provide the rationale for clinical trials to confirm or refute these findings.