The Body Fluid Estimation Techniques in Critically Ill Patients; Evolution from Static to Dynamic Modalities: A Scoping Review

Background: Accurate estimation of fluid status in critically ill patients is vital to improving outcomes and guiding resuscitation strategies. Both fluid overload and hypovolemia are independently associated with increased morbidity, prolonged ICU stays, and mortality. Objective: The study aims at evaluating past and current methodologies for assessing body fluid status in critically ill patients, emphasizing their accuracy, feasibility, and clinical applicability, especially in low-resource settings. Methodology: Following PRISMA 2020 guidelines, we conducted a systematic search of PubMed, EMBASE, and Cochrane Library databases from 1990 to 2024. Studies were included if they evaluated the diagnostic performance, clinical impact, or usability of fluid assessment techniques in adult ICU populations. We identified and analyzed 64 studies encompassing a wide range of modalities. Key data were extracted and synthesized into thematic categories, including static, dynamic, and advanced hemodynamic parameters. Results: Traditional methods like Central Venous Pressure (CVP) and Pulmonary Artery Catheter (PAC) were found to have poor predictive accuracy. Dynamic bedside assessments, such as Passive Leg Raise (PLR) and Stroke Volume Variation (SVV), showed superior reliability. Point-of-care ultrasound (POCUS) and newer tools like the VEXUS and VExLUS protocols emerged as promising, especially in resource-limited settings. Advanced hemodynamic monitoring using PiCCO, LiDCO, and bioimpedance devices provided high accuracy but faced barriers to implementation due to cost and infrastructure. Microcirculatory parameters such as ScvO₂, Pv-aCO₂ gap, and lactate levels were useful adjuncts in multimodal strategies. Conclusion: A multimodal, context-sensitive approach integrating bedside assessments, ultrasound, and microcirculatory markers is recommended for fluid management in critical care. In low-resource settings, simplified protocols utilizing POCUS and clinical scoring systems can guide safe and effective decision-making.