Assessment of pulmonary edema based on extravascular thermal volume in dogs

To establish criteria of pulmonary edema by extravascular thermal volume (ETV), ETV and a roentgenogram of the thorax were compared in normal and experimental hydrostatic pulmonary edema dogs. ETV was measured by the double indicator dilution technique using heat as a diffusible indicator and sodium ions as a non-diffusible indicator (thermal-Na method). Mean ETV in 14 dogs under physiologic conditions was 8.20 +/- 1.44 ml/kg. Comparison of ETV with the roentgenogram indicated the density of thoracic the roentgenogram to increase when ETV exceeded 11 ml/kg. Pulmonary edema was recognized clearly in the thoracic roentgenogram at more than 15 ml/kg of ETV. Further increase in ETV did not occur with additional radiographic change. ETV was significantly (P < 0.01) correlated with arterial oxygen tension (PaO2) but not statistically correlated with colloid oncotic pressure (COP), pulmonary arterial wedge pressure (PAWP) or PAWP-COP. Measurement of ETV would thus, appear to be a reliable method for evaluating the severity of pulmonary edema, which has been difficult to diagnose by roentgenography and should facilitate the early diagnosis and management of pulmonary edema.