Current fluid management practice in critically ill adults on continuous renal replacement therapy: A binational, observational study.

Introduction In critically ill patients undergoing continuous renal replacement therapy (CRRT), a positive fluid balance (FB) is associated with adverse outcomes. However, current FB management practices in CRRT patients are poorly understood. We aimed to study FB and its components in British and Australian CRRT patients to inform future trials. Methods We obtained detailed electronic health record data on all fluid-related variables during CRRT and hourly FB for the first seven days of treatment. Results We studied 1,616 patients from three tertiary ICUs in two countries. After the start of CRRT, the mean cumulative FB became negative at 31 hours and remained negative over seven days to a mean nadir of -4.1 L (95% confidence intervals (CI) of -4.6 to -3.5). The net ultrafiltration (NUF) rate was the dominant fluid variable (-67.7 mL/h; SD 75.7); however, residual urine output (-34.7 mL/h; SD 54.5), crystalloid administration (48.1 mL/h; SD 44.6), and nutritional input (36.4 mL/h; SD 29.7) significantly contributed to FB. Patients with a positive FB after 72 hours of CRRT, were more severely ill, required high-dose vasopressors and had high lactate concentrations (5.0 mmol/L; IQR 2.3 - 10.5). A positive FB was independently associated with increased hospital mortality (OR 1.70; 95% CI; p=0.004). Conclusion In the study ICUs, most CRRT patients achieved a predominantly NUF-dependent negative FB. Patients with a positive FB at 72 hours had greater illness severity and haemodynamic instability. Achieving equipoise for conducting trials that target a negative early FB in such patients may be difficult.