Early Net Ultrafiltration during Continuous Renal Replacement Therapy: Impact of Admission Diagnosis and Association with Mortality

Abstract

<b><i>Introduction:</i></b> Continuous renal replacement therapy (CRRT) is common in the intensive care unit (ICU) but a high net ultrafiltration rate (UF<sub>NET</sub>) calculated with daily data may increase mortality. We aimed to study early UF<sub>NET</sub> practice using minute-by-minute CRRT machine recordings and to assess its association with admission diagnosis and mortality. <b><i>Methods:</i></b> We studied CRRT treatments in three adult ICUs over 7 years. We calculated early UF<sub>NET</sub> rates minute-by-minute and categorized UF<sub>NET</sub> into tertiles of mean UF<sub>NET</sub> in the first 72 h and admission diagnosis. We applied Cox-proportional hazards modelling with censoring of patients who died within 72 h. <b><i>Results:</i></b> We studied 1,218 patients, 154,712 h, and 9,282,729 min of CRRT (5,702 circuits). Mean early UF<sub>NET</sub> was 1.52 (1.46–1.57) mL/kg/h. Early UF<sub>NET</sub> tertiles were similar to, but somewhat higher than, previously reported values at 0.00–1.20 mL/kg/h, 1.21–1.93 mL/kg/h, and >1.93 mL/kg/h. UF<sub>NET</sub> values were similar whether evaluated at 24 or 72 h or for the entire duration of CRRT. There was, however, significant variation in UF<sub>NET</sub> practice by admission diagnosis: higher in respiratory diseases (pneumonia <i>p</i> = 0.01, other <i>p</i> < 0.0001) and cardiovascular disease (<i>p</i> = 0.005) but lower in cardiothoracic surgery (<i>p</i> = 0.04), renal (<i>p</i> = 0.0003) and toxicology-associated diagnoses (<i>p</i> = 0.01). Higher UF<sub>NET</sub> was associated with an increased hazard of death, HR 1.24 (1.13–1.37), independent of admission diagnosis, weight, age, sex, presence of end-stage kidney disease, and severity of illness. <b><i>Conclusion:</i></b> Early UF<sub>NET</sub> practice varies significantly by admission diagnosis. Higher early UF<sub>NET</sub> is independently associated with mortality. Impacts of UF<sub>NET</sub> on mortality may vary by admission diagnosis. Further work is required to elucidate the nature and mechanisms responsible for this association.