Routine 24-Hour Fluid Balance and Short-Term Fluid Change in Critically Ill Patients: A Pro-spective Agreement Study

BACKGROUND Twenty-four-hour fluid balance is routinely used as a surrogate marker of net fluid change in critically ill patients and frequently influences bedside clinical decision-making, including assessment of volume status and fluid management strategies. However, despite its widespread use in intensive care practice, the reliability and accuracy of this routinely recorded parameter as a measure of short-term fluid change remain uncertain. MATERIAL AND METHODS We conducted a prospective multicenter observational study comparing cumulative 24-hour fluid balance with 24-hour body weight change measured over identical time intervals in adult patients admitted to the intensive care unit (ICU). Paired measurements were collected and analyzed to evaluate the agreement between these 2 commonly used approaches for estimating short-term fluid changes. Agreement was assessed using Bland-Altman analysis, including regression-based evaluation of proportional bias. Clinically acceptable agreement was predefined as a difference within ± 1 kg between methods. RESULTS A total of 360 paired observations were analyzed. The mean bias between methods was small (0.082 kg), indicating minimal systematic difference at the population level. However, agreement at the individual level was poor, with wide 95% limits of agreement (-2.1 to +2.264 kg), exceeding the predefined threshold for clinical acceptability. Clinically significant disagreement (> 1 kg) occurred in 30.2% of observations. Proportional bias was present, with increasing discrepancy between methods across the range of measured values, suggesting that disagreement was not consistent across different levels of fluid change. CONCLUSIONS Routinely charted 24-hour fluid balance demonstrates clinically unacceptable agreement with body weight change and should not be considered an interchangeable measure of short-term fluid change in critically ill patients. An integrated approach combining fluid balance assessment, serial body weight measurements, and comprehensive clinical evaluation is recommended to improve assessment of fluid status and guide individualized patient management.