Electronic bed weighing vs daily fluid balance changes after cardiac surgery

The purpose of this study is to establish the validity and reliability of measuring weight in critically ill patients with electronic weighing beds.

All patients admitted to a private intensive care unit (ICU) after cardiac surgery over a 7-month period were weighed on admission and then twice daily (1200 and 2400 hours) using electronic weighing beds (Hill-Rom, Batesville, AR). For each measurement, nonremovable items were recorded, and an average value was deducted from measured weight. We compared differences in body weights (BWs) between 2 consecutive 12-hour periods with the corresponding fluid balance (FB). In addition, we compared weights obtained with electronic weighing beds with those obtained with a regular calibrated scale on ICU discharge.

We obtained data in 103 patients for 414 (75.5%) of 548 of all possible BW measurements. On average, we identified a total of 3.5 kg (SD, 1.4) of nonremovable items on patients' beds. The correlation between 12-hourly changes in BW and FB was weak (r = 0.28; 95% confidence interval [CI], 0.17-0.39), even after correction for insensible fluid losses (r = 0.27; 95% CI, 0.15-0.38) and when only values obtained in intubated patients were taken into account (r = 0.34; 95% CI, 0.16-0.49). Similarly, limits of agreements were wide (95% CI, -3.3 to 3.5 kg). There was also poor agreement between weights obtained on electronic beds and those obtained on the regular scale on ICU discharge (95% CI, -7.6 to 7.6 kg).

Body weight measured by electronic weighing beds does not seem sufficiently robust or accurate to replace daily FB in ICU. The clinical value of purchasing such beds remains uncertain.