[Accumulated fluid balance in patients admitted to the ICU: is it really reliable?]

In most of the textbooks, it is considered that the balance calculated after admission and the losses measured and/or estimated is an inexact way of establishing the real balance. Thus daily monitoring of the weight variations is recommended as a single possible alternative. On the other hand, there are few studies that have strictly studied the reliability of the fluid balance calculated. We also have not found any study in middle-long stay critical patients. These circumstances have led us to design an observational prospective study that will allow us to know if the accumulated balance calculated after admission and loses adequately reflect the weight changes in middle-long stay patients. We include 20 patients who were weighed every 48 hours (at least 3 times each one) and we compare the weight changes with the balances calculated. We find that, above all after the 6th day, the accumulated balance calculated adequately reflected the weight changes (mean error/day < 250 ml), regardless of the presence or not of fever, sweat, oral diet, feces or mechanical ventilation. When weight on admission to the ICU was less than 75 kg, the changes in the balance calculated adjusted even more to the weight change, the contrary occurring when the weight was greater than 75 kg. These findings suggest that the accumulated balance calculated represents a valid alternative to daily weighing of the patients and that factors such as body mass and/or surface should be taken into account to reach more exact estimations.