Peribronchial electrical admittance measures lung edema and congestion in the dog

A new method has been developed to detect interstitial pulmonary edema. This method utilizes the unique arrangement of air and interstitial fluid within the lung. A 1.3-mm-diam twin catheter electrode was wedged in a peripheral airway of the lung. The electrical impedance measured at 35 kHz between these catheter-tip electrodes was 1,540 +/- 240 omega (mean +/- SD; n = 10) in the anesthetized closed-chest dog. Intravenous infusion of 1-3 liters 0.154 M NaCl increased extravascular water per gram of dry lung from a control value of 3.54 +/- 0.27 to 4.1-5.14. Peribronchial electrical impedance decreased in proportion to the amount of saline infused reaching a minimum of 550 omega. No signs of alveolar flooding were present during the experiments. Linear regression performed on peribronchial electrical admittance (PEA) as a function of extravascular water per gram of dry lung (ELW) resulted in the following relationship: PEA = 0.72 ELW - 1.81; r = 0.95. It is concluded that this method is a sensitive quantitative measure of lung interstitial fluid and can detect pulmonary edema and congestion in the dog lung before alveolar flooding occurs.