Assessment of acute pulmonary edema in dogs by electrical impedance imaging

Acute pulmonary edema was assessed quantitatively in 12 experiments on six anesthetized dogs. Thirty-two copper foil electrodes were placed around each animal's thorax at the level of the third intercostal space. A real-time electrical impedance tomograph was used to form images of the electrical admittivity of the thorax in and near the plane of these electrodes. The lungs were identified by studying the change in admittivity associated with inspiration. Mean admittivity in these lung regions was assessed at 40-min intervals for the next 3-6 hours. In six control experiments, each having a duration of 200 min, the initial admittivity of the lung regions was 102 +/- 16(SD) mS/m. Lung admittivity usually increased during the first 80 min, and then remained within 2 mS/m of its value at 80 min for the remaining 120 min. In six experiments with pulmonary edema, an initial period of change followed by stability was observed. When stability had been attained, 0.07 ml/kg of oleic acid was injected slowly into a central venous site. Five animals received oleic acid, the sixth received a sham injection of saline. In the five receiving oleic acid, lung admittivity rose steadily for the remainder of the experiment. The increase in lung admittivity in these five animals was between 4 and 16 mS/m. In the sham injected experiment, the lung admittivity changed by 1 mS/m. We conclude that impedance imaging can provide semiquantitative assessment of the development of acute pulmonary edema.