Assessment of hydrosodic balance by impedancemetry in intensive care: a monocentric prospective study, the EBaHIR study

Background: Fluid overload (FO) is frequent in critically ill patients and is linked to adverse outcomes. Conventional assessment methods – clinical signs, body weight variation, and cumulative fluid balance (cumFB) – have limitations during prolonged intensive care unit (ICU) stays. Bioelectrical impedance analysis (BIA) is a non-invasive technique that may provide a more accurate evaluation of hydration status. This study assessed the ability of BIA to detect FO in ICU patients compared with standard clinical and ultrasound methods. Methods: We performed a prospective observational study in a medical ICU, including adults expected to stay ≥7 days. Hydration status was monitored daily by clinical exam, ultrasound, weight change, and cumFB. From Day 3, BIA measurements total body water (TBW), extracellular water (ECW), intracellular water (ICW), third-space volume, ECW/TBW ratio, ECW/ICW ratio, excess volume, and phase angle were obtained. FO was defined by BIA-derived criteria. Agreements and correlations were analyzed. Results: Twenty-one patients (median age 69.5 years; 66.7% male) underwent 88 BIA assessments. Clinical FO was present in 55.7% of cases, whereas BIA identified FO in 82.8% (excess volume >1 L). In patients without clinical signs, BIA still revealed hidden fluid excess. Weight change correlated with cumFB ( ρ = 0.8), but conventional indicators showed weak or no correlation with BIA parameters. Patients with significant weight loss (<–5%) often remained overhydrated according to BIA. Conclusion: BIA detects subclinical FO overlooked by standard methods, supporting its integration into ICU fluid management and de-resuscitation strategies. Larger studies are needed to confirm its prognostic value.