Fluid balance versus weighing: A comparison in ICU patients: A single center observational study

Abstract

Background: The fluid balance is a critical parameter in intensive care units (ICU) as it provides information about the patient's volume status. However, the accuracy of fluid balance measurements is often compromised due to the complexity and repetition of actions involved. Additionally, the fluid balance could be recalculated for insensible fluid loss. Weighing is an alternative method to estimate the patient's volume status. Built-in scales in beds make patient weighing easier and less time-consuming, allowing clinicians to intervene more quickly on existing treatments.

Aim: This study compares fluid balance, and body weight changes over time in ICU patients. Furthermore, it seeks to determine the degree of congruence between the fluid balance corrected for insensible fluid loss and daily body weight in ICU patients.

Methods: A single-center observational study was conducted in an ICU of a university hospital. All consecutive patients admitted to a bed with an integrated weighing scale were eligible. Exclusion criteria were (1) body weight ≥254,4 kilograms; (2) oral nutrition; (3) a flush catheter or balance; (4) only a single weight measurement; (5) delta body weight change of ≥5kg in 12 hours. Weights and fluid balances were obtained every 12 hours.

Results: We obtained 2282 measurements (n = 187 patients). The correlation between weight and fluid balance was weak (r = 0.274). After adjusting the fluid balance for insensible fluid loss, the correlation remained weak (r = 0,268). Bland Altman analysis revealed a wide confidence interval for both the fluid balance and corrected fluid balance versus weight.

Conclusion and implications of key findings: This study shows a weak correlation between weight and fluid balance. Therefore, when monitoring the volume status in the ICU, fluid balance and weight should both be taken into account. This two-pronged approach is crucial because it provides more control over erroneous fluid balance or weighing measurements.

Fig 1. Included measurements.

Fig 2. Bland Altman plot for changes in fluid balance and simultaneous body weight.

X-axis, mean value of delta fluid balance (DFB) and delta weight (DW). Y-axis, difference between delta fluid balance (DFB) and delta weight (DW).

Fig 3. Bland Altman plot for changes in the corrected fluid balance and simultaneous body weight.

X-axis, mean value of delta corrected fluid balance (DCFB) and delta weight (DW). Y-axis, difference between delta corrected fluid balance (DCFB) and delta weight (DW).