Clinical Parameters Associated with Achieving Negative Fluid Balance in Critically Ill Patients: A Retrospective Cohort Study

Background/Objectives: Fluid overload in critically ill patients is linked to adverse outcomes. While resuscitation strategies are well established, guidance for the de-resuscitation phase remains limited. This study aimed to identify clinical factors associated with diuretic response and achieving negative fluid balance (FB) in critically ill patients. Methods: We conducted a single-center, retrospective cohort study of ICU patients who received intravenous furosemide between 2017 and 2023. A CHAID (Chi-square Automatic Interaction Detector) decision tree identified clinical variables associated with fluid removal after the first dose, and a mixed-effects model analyzed repeated measurements. Results: The cohort comprised 1764 patients over 6632 ICU days. Mean arterial pressure (MAP) was the strongest predictor of negative FB. MAP ≤ 75 mmHg yielded minimal negative FB (−33 ± 1054 mL/24 h); MAP 75–90 mmHg yielded intermediate negative FB (−467 ± 1140 mL/24 h); and MAP > 90 mmHg produced the greatest negative FB (−899 ± 1415 mL/24 h; p < 0.001). Secondary associations varied by MAP: creatinine at low MAP, blood urea nitrogen at mid-range MAP, and SOFA score at high MAP, all inversely related to negative FB. In mixed-effects analyses, each 1 mmHg MAP increase was associated with 23.3 mL greater fluid removal (p < 0.001). Independent factors linked to reduced negative FB included vasopressor use (noradrenaline), elevated creatinine, and higher SOFA scores. Conclusions: In this cohort, MAP was significantly associated with the likelihood of achieving a negative fluid balance during de-resuscitation. Conversely, vasopressor use, renal dysfunction, and higher illness severity were linked to reduced diuretic responsiveness. These findings support individualized de-resuscitation strategies.