The Impact of Fluid Balance on Clinical Outcomes in ICU Patients with Pulmonary Arterial Hypertension: A Retrospective Analysis using MIMIC-IV

Pulmonary Arterial Hypertension (PAH) is a significant comorbidity that can complicate the care of patients in the Intensive Care Unit (ICU). PAH's hemodynamic burden and systemic effects add complexity to managing fluid balance, ventilatory support, and other critical care interventions. This study aims to investigate the impact of fluid balance in ICU patients with PAH.

We conducted a retrospective cohort study using the MIMIC-IV v3.1 database. Patients with diagnosed PAH (ICD-9: 4160; ICD-10: I270) and complete ICU records were included. Exclusions were applied for missing data, duplicate ICU stays, and secondary causes of pulmonary hypertension. An initial cohort of 178 patients was identified. Further data validation led to a final cohort comprising 102 patients. Analyses were conducted in Google BigQuery and Python-based tools (Google Colab).

Among 102 patients, 77 (75.4%) had a positive fluid balance, and 25 (24.5%) had a negative balance. Positive fluid balance was associated with higher ICU mortality (14.49% vs. 5.88%), shorter ICU stays (2.29 vs. 3.06 days), and a 74% increase in ICU mortality odds (OR: 1.74, 95% CI: 1.10–2.85). The lowest ICU mortality was seen in patients with net fluid balance between -2000 mL and +2000 mL. Severely positive balance (>+5000 mL) was associated with the highest ICU mortality (19%) and longest ICU LOS (6.16 days).

This study highlights the critical importance of fluid balance in PAH patients, a population uniquely susceptible to right ventricular failure. The findings suggest that even modest positive fluid balance may worsen outcomes, supporting prior physiologic models linking volume overload to RV dysfunction. While limited by retrospective design and lack of hemodynamic data, the results underscore the potential benefit of individualized fluid strategies and the selective use of advanced monitoring. Further prospective research is needed to define safe fluid thresholds and guide therapy in this high-risk group.

Our findings suggest that both excessive positive and severe negative fluid balance may be detrimental in ICU patients with PAH. A moderate fluid balance range (-2000 mL to +2000 mL) showed the most favorable outcomes.