[The fluid balance in the critically ill patient]

In the critically ill patient the hemodynamic management is essential. Usually the hemodynamic status is estimated by the measurement of the intravascular pressure or volume and by computing the fluid balance, while the change in body weight estimates the total body water. The fluid balance is computed by subtracting the fluid output to the input. Although the input (fluids, drugs, infusion.) are well known, the output are difficult to correctly compute, because they depend on several factors such as the body-room temperature, amount of humidity and may change with time. Aim of this study was to prospectively evaluate the accuracy of the fluid balance compared to the body weight measured by a dedicated mattress (Hill-Rom).

Fifteen critically ill patients were enrolled (mean age of 63.2+/-19.7 years, body mass index of 24.9+/-3.5 kg/m2) and the measurements were computed every 8 hours. The data were analyzed by the Bland-Altman test.

Four-hundred and seventy-two measurements for a mean intensive care stay of 12.3.+/-7.3 days were computed. The Bland-Altamn showed a great inaccuracy, because the agreement (the difference between the 2 methods) was poor with a standard deviation of 1 840 L.

Although the fluid balance was not accurate, the only body weight without any intravascular measurement is not helpful for a correct clinical hemodynamic management of the patient.