Estimation of normal lung weight index in healthy female domestic pigs

Abstract

Introduction Lung weight is an important study endpoint to assess lung edema in porcine experiments on acute respiratory distress syndrome and ventilatory induced lung injury. Evidence on the relationship between lung–body weight relationship is lacking in the literature. The aim of this work is to provide a reference equation between normal lung and body weight in female domestic piglets.

Materials and methods 177 healthy female domestic piglets from previous studies were included in the analysis. Lung weight was assessed either via a CT-scan before any experimental injury or with a scale after autopsy. The animals were randomly divided in a training (n = 141) and a validation population (n = 36). The relation between body weight and lung weight index (lung weight/body weight, g/kg) was described by an exponential function on the training population. The equation was tested on the validation population. A Bland–Altman analysis was performed to compare the lung weight index in the validation population and its theoretical value calculated with the reference equation.

Results A good fit was found between the validation population and the exponential equation extracted from the training population (RMSE = 0.060). The equation to determine lung weight index from body weight was: ${\text{Lung}} {\text{Weight}} {\text{Index}} \left(\frac{{\text{g}}}{{\text{kg}}}\right)=26.26*{10}^{-0.011*{\text{Body}} {\text{Weight}} \left({\text{kg}}\right)}.$

At the Bland and Altman analyses, the mean bias between the real and the expected lung weight index was − 0.26 g/kg (95% CI − 0.96–0.43), upper LOA 3.80 g/kg [95% CI 2.59–5.01], lower LOA − 4.33 g/kg [95% CI = − 5.54–(− 3.12)].

Conclusions This exponential function might be a valuable tool to assess lung edema in experiments involving 16–50 kg female domestic piglets. The error that can be made due to the 95% confidence intervals of the formula is smaller than the one made considering the lung to body weight as a linear relationship.