Estimation of fluid status changes in critically ill patients: fluid balance chart or electronic bed weight?

Monitoring of fluid balance (FB) can be achieved by subtracting recorded fluid output from input or by measuring changes in body weight (BW). The latter approach is difficult in the critically ill. Recently, hospital beds have become available with the ability to directly weigh patients in the intensive care unit (ICU) patients directly. We sought to compare FB estimates obtained by these 2 methods in a cohort of critically ill patients.

Between November 2010 and May 2011, all patients admitted in our ICU for more than 2 consecutive days and nursed on a Hill-Rom (Batesville, Ind) Total Care bed were weighed daily at midnight hours. Fluids charting was done by electronic spreadsheet with automated 24 hours calculation. Differences in BW and FB between 2 consecutive days were compared using correlation and Bland-Altman analysis. Corrections for unmeasured fluids losses were performed using a predetermined formula based on peak temperature and intubation status.

We obtained complete data in 160 (31%) of 504 admissions exceeding 2 days (153 patients) resulting in 435 data points. The change in BW over 24 hours and FB for the same period was only weakly correlated before (r = 0.34; P < .001; Fig. 1) or after correction for insensible fluid losses (r = 0.34; P < .001). On Bland-Altman plot, the mean bias was small (0.07 kg), but the 95% limits of agreement, very large (-5.8 and 6.0 kg). The lack of agreement increased with the magnitude of the changes.

Obtaining daily weights in ICU patients proved difficult. Compliance was poor. The correlation between changes in BWs and FB was weak. Further studies are required to establish if accurate and reproducible daily weighing of ICU patients is feasible.