Agreement Between Measured Weight and Fluid Balance in Mechanically Ventilated Children in Intensive Care

Abstract

OBJECTIVES: To investigate the agreement between change in body weight (BW) and fluid balance (FB), and the precision and safety of BW measurement in mechanically ventilated infants in intensive care. DESIGN: Prospective observational study. SETTING: Tertiary PICU. PATIENTS: Infants following cardiac surgery, at baseline, 24 hours, and 48 hours. INTERVENTIONS: BW and FB measurement at three time points. MEASUREMENTS AND MAIN RESULTS: Between May 2021 and September 2022, we studied 61 children. The median age was 8 days (interquartile range [IQR], 1.0–14.0 d). The median BW at baseline was 3,518 g (IQR, 3,134–3,928 g). Change in BW was –36 g (IQR, –145 to 105 g) and –97 g (IQR, –240 to –28 g) between baseline and 24 hours, and between 24 and 48 hours, respectively. Change in FB was –82 mL (IQR, –173 to 12 mL) and –107 mL (IQR, –226 to 103) between baseline and 24 hours, and between 24 and 48 hours, respectively. In Bland-Altman analyses, the mean bias between BW and FB at 24 and 48 hours was 54 g (95% CI, 12–97) and –43 g (95% CI, –108 to 23), respectively. This exceeded 1% of the median BW, and limits of agreement ranged from 7.6% to 15% of baseline BW. The precision of paired weight measurements, performed sequentially at each time interval, was high (median difference of ≤1% of BW at each time point). The median weight of connected devices ranged from 2.7% to 3% of BW. There were no episodes of tube or device dislodgments and no change in vasoactive therapies during weight measurements. CONCLUSIONS: There is moderate agreement between the changes in FB and BW, albeit greater than 1% of baseline BW, and the limits of this agreement are wide. Weighing mechanically ventilated infants in intensive care is a relatively safe and precise method for estimating change in fluid status. Device weight represents a relatively large proportion of BW.