Current formulas for water requirements produce different estimates

Weight-based and energy-based formulas are used to estimate the water requirements of patients receiving nutrition support, yet these formulas have not been validated nor quantitatively compared with one another. The objective of this study was to determine if there was agreement among commonly used formulas for estimating water requirements.

This cross-sectional survey design was from the continuous National Health and Nutrition Examination Survey 1999-2004. To determine estimated water requirements for each participant, 2 weight-based formulas were used (30 mL/kg body weight and an adjusted body weight formula) and 3 energy-based formulas based on 1 mL/kcal (energy needs estimated by the Harris Benedict, Mifflin St Jeor, and National Research Council equations). Simple linear regression was performed between each pair of formulas to determine correlations. The regression line was then compared to the line of equality to determine agreement between pairs.

Although the 5 formulas were strongly correlated to each other (|r| > 0.7), they demonstrated poor agreement with one another with significant differences when the regression line was compared to the line of equality.

Current formulas that estimate the water requirements of patients receiving enteral nutrition and parenteral nutrition all compute a dissimilar quantity of water. The consequences of these estimates could result in major differences in water intake recommendations and prescriptions between patients or in the same patient, thus suggesting a need for improved standardization of practice for estimating water requirements in clinical practice.