The thermal-dye method of lung water measurement is reliable at a low cardiac output

The measurement of lung water by the thermal-dye double indicator dilution technique was evaluated in dogs with normal and edematous lungs during a state of reduced cardiac output. The technique used cold indocyanine green dye to measure extravascular thermal volume (EVTV) as an estimate of extra-vascular lung water (EVLW). Anesthesia was maintained with pentobarbital. In 15 of 21 animals, pulmonary edema was first induced with oleic acid (0.75 to 0.18 ml/kg). Cardiac output (CO) was then decreased by a combination of propranolol and slow exsanguination (mean CO reduction to 36% of baseline). Extravascular lung water produced in this model ranged from 1.4 to 30.2 ml/kg. Predetermination measurements of EVTV correlated closely with EVLW as determined by gravimetric analysis (EVTV = 1.1 EVLW + 4.7 ml/kg, n = 21, r = 0.93, P < 0.001). Thermodilution cardiac output measured in the abdominal aorta (used in the calculation of the EVTV) correlated well with simultaneous measurements of cardiac output by both indocyanine green dye dilution and pulmonary artery thermodilution (r = 0.86 and r = 0.88, respectively, pretermination). The thermal-dye technique appears to provide an accurate reflection of lung water in normal and edematous lungs, even in the presence of a low cardiac output.