Pilot study of fluid shift assessment using bioelectrical impedance spectroscopy

Maintaining fluid balance between intracellular and extracellular compartments is essential for physiological stability, yet disturbances in this equilibrium are common in conditions such as dehydration, sepsis, and perioperative stress. Traditional techniques for quantifying body water distribution, including isotope dilution, are accurate but invasive and unsuitable for repeated or bedside monitoring. Bioelectrical impedance spectroscopy (BIS) offers a non-invasive, rapid, and frequency-dependent approach to estimating total body water (TBW), extracellular water (ECW), and intracellular water (ICW), making it a promising candidate for real-time fluid assessment. This pilot study evaluated the sensitivity of BIS in detecting controlled fluid shifts under three conditions: intravenous infusion of graded volumes of lactated Ringer's solution, incremental gravity-drip infusion, and oral ingestion of water in divided portions. BIS measurements demonstrated reproducible, volume-dependent changes in TBW, ECW, and ICW, with distinct temporal patterns characterized by early rises, redistribution phases, and stabilization plateaus. Moderate fluid loads of 500-1000 mL yielded stable and sustained hydration profiles, whereas smaller volumes induced minimal shifts and larger volumes produced greater variability, reflecting regulatory corrections. These findings support the feasibility of BIS as a practical bedside tool for monitoring hydration dynamics. Larger clinical studies are guaranteed to confirm its role in fluid management for surgical and critically ill populations.