P1460MEDIATORS OF THE IMPACT OF HOURLY NET ULTRAFILTRATION RATE ON MORTALITY IN CRITICALLY ILL PATIENTS RECEIVING CONTINUOUS RENAL REPLACEMENT THERAPY

Abstract

Abstract Background and Aims During continuous renal replacement therapy (CRRT), a high net ultrafiltration (NUF) rate is associated with increased mortality. However, it is unknown what might mediate its putative effect on mortality. This study aims to investigate whether the relationship between early (first 48h) NUF and mortality is mediated by fluid balance (FB), hemodynamic instability or low potassium or phosphate blood levels. Method We performed a retrospective, observational study in patients treated with CRRT within 14 days of ICU admission who survived >48 hours. The primary outcome was hospital mortality. We applied multiple mediation analysis to identify possible mediators of NUF’s putative impact on mortality. Results We studied 347 patients [median (interquartile range) age: 64 (53–71) years and Acute Physiology and Chronic Health Evaluation (APACHE) III score: 73 (54–90)]. After adjustment for confounders, compared with a NUF<1.01 ml/kg/h, a NUF rate > 1.75 mL/kg/h was associated with significantly greater mortality (adjusted odds ratio [aOR], 1.15 [95%CI, 1.03 to 1.29]; p = 0.011). Adjusted univariable mediation analysis found no suggestion of a causal mediation effect for blood pressure, vasopressor therapy, or potassium levels, but identified a possible effect for FB (average causal mediation effect (ACME), 0.95 [95%CI, 0.90 to 0.99]; p = 0.062) and percentage of phosphate measurements with hypophosphatemia (ACME, 0.96 [95%CI, 0.92 to 1.00]; p = 0.055). However, on multiple mediator analysis, such variables lost any suggestion of a significant effect. In contrast, NUF rate remained associated with mortality even in their presence (average direct effect, 1.24 [95%CI, 1.11 to 1.40]; p < 0.001). Conclusion An early NUF greater than 1.75 mL/kg/h was independently associated with increased hospital mortality. Its putative effect was not mediated by FB, low blood pressure, vasopressor use, hypokalemia or hypophosphatemia.