AGREEMENT BETWEEN BIOELECTRICAL IMPEDANCE ANALYSIS, DAILY BODY WEIGHT, AND INTAKE-OUTPUT CHARTING FOR ASSESSING FLUID BALANCE IN SEPSIS AND SEPTIC SHOCK: A PROSPECTIVE OBSERVATIONAL COHORT STUDY FROM AN INDIAN INTENSIVE CARE UNIT

Abstract

Background and Aims: Assessment of cumulative fluid balance in sepsis and septic shock is clinically important but difficult in routine intensive care practice. Intake-output charting is widely used but may be affected by documentation errors and unmeasured losses. Daily body weight reflects net mass change but is logistically difficult in critically ill patients. Bioelectrical impedance analysis (BIA) may provide additional information on body-water compartments. This study evaluated the relationship and agreement between intake-output balance, daily body weight, and BIA derived body-water measurements in adult patients with sepsis and septic shock. Materials and Methods: This prospective observational cohort study was conducted in adult ICU patients with sepsis or septic shock between 20 April 2025 and 29 May 2026. Daily fluid input, output, body weight, and BIA-derived total body water (TBW), intracellular water (ICW), and extracellular water (ECW) were recorded. Daily net fluid balance was calculated as total input minus total output. Incremental cumulative fluid balance was derived as the running sum of daily net balance from each patient's first recorded measurement. Correlations between fluid balance and BIA/weight variables were assessed using absolute daily values and change-from-baseline values. Agreement was assessed using Bland-Altman analysis. Results: Seventy patients contributed 230 paired daily observations. Mean age was 59.5 +/- 16.6 years, APACHE II score was 20.1 +/- 6.8, and SOFA score was 11.5 +/- 3.7. Mean daily fluid input was 2866 +/- 730 mL, output was 1420 +/- 494 mL, and daily net balance was +1447 +/- 955 mL. Mean daily body weight was 69.7 +/- 13.8 kg. BIA derived TBW, ICW, and ECW were 36.4 +/- 6.1 L, 20.2 +/- 3.8 L, and 14.6 +/- 2.3 L, respectively. Absolute daily body weight correlated weakly with daily net balance (r = 0.13, p = 0.045), while TBW and ECW did not show meaningful absolute-value correlations with daily net balance. In repeated-measures change analysis, incremental cumulative balance showed no meaningful association with change in body weight (r = 0.01, p = 0.909), but showed weak associations with change in TBW (r = 0.27, p < 0.001) and ECW (r = 0.24, p = 0.003). Bland-Altman analysis demonstrated wide limits of agreement between methods. Conclusion: In adult Indian ICU patients with sepsis and septic shock, intake-output balance, daily body weight, and BIA-derived body-water measurements were not interchangeable. BIA-derived TBW and ECW trends may provide useful adjunctive information on fluid accumulation and compartmental shifts but should complement rather than replace meticulous intake-output stewardship.(CTRI:2025/04/085655). charting, serial clinical assessment, and individualized fluid