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Association Between Fluid Intake and Mortality in Critically Ill Patients with Negative Fluid Balance: A Retrospective Cohort Study
Shen Y, Huang X, Zhang W. Critical Care. 2017; 21: 104-112.
Study Question: Does the degree of negative fluid balance (FB) impact the outcome of critically ill patients with a negative FB?
Study Description: This was a single-center, retrospective cohort study. Adult patients admitted to the ICU for > 48 hours who achieved a negative FB at 48 hours were included. Patients were stratified into four levels of fluid intake (level 1: < 30 mL/kg/48 hours, level 2: 30 – 59 mL/kg/48 hours, level 3: 60 – 89 mL/kg/48 hours and level 4: > 90 mL/kg/48 hours) and FB (level 1: - 19 to 0 mL/kg/48 hours, level 2: -20 to -39 mL/kg/48 hours, level 3: -40 to -59 mL/kg/48 hours and level 4: ≤ -60 mL/kg/48 hours). The primary outcome was hospital mortality.
Results: In total, 2068 patients were included; 604 patients did not survive (29.2%). Overall, FB did not impact outcomes (-21.5 vs. -20.9 mL/kg/48 hours, p = 0.231). Increased fluid intake was associated with decreased mortality in a stepwise fashion relative to level 1 (level 2 OR 0.73, 95% CI 0.56 – 0.96, p = 0.024; level 4 OR 0.47, 95% CI 0.3 – 0.74, p = 0.001). All levels had a trend towards lower mortality, but only a very negative FB significantly decreased hospital mortality (level 4 OR 0.56; 95% CI 0.33 – 0.95, p = 0.034).
Conclusion(s): Increased fluid intake and urinary output were associated with improved mortality, while achieving a more negative FB did not impact outcomes.
Perspective: Fluid management is a challenging area of critical care management. It is required for hemodynamic stabilization but can be a risk factor for increased mortality. Multiple studies in various populations have demonstrated that a positive FB can be predictive of mortality. In the present study, patients who had larger fluid intake and urinary output had a lower risk of mortality. Due to the retrospective nature of the study, it is unclear if the association of increased urinary output with mortality was a function of higher fluid administration. Additionally, due to potential selection bias and other confounding variables, it is unknown what the optimal fluid intake should be.