Effect of air embolism on the measurement of extravascular lung thermal volume

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Abstract
To determine the accuracy of thermal-dye indicator-dilution measurements of lung water during perfusion abnormalities, air was embolized into the lungs of 10 dogs anesthetized with pentobarbital and mechanically ventilated. A control period was followed by a period of air injection (10 ml) and subsequent air infusion (E1), a 2nd period of air injection and infusion (E2) and a recovery period. Thermal and dye-dilution curves were obtained during each period and cardiac output (CO), total thermal volume, intravascular volume and extravascular thermal volume (ETV) were calculated. Pulmonary arterial pressure (Ppa) increased from 16 .+-. 2 cm H2O during control to 29 .+-. 3 cm H2O during E1 and to 40 .+-. 3 cm H2O during E2 and decreased to 21 .+-. 2 cm H2O during recovery. CO did not change, and pulmonary vascular resistance changed in a pattern similar to Ppa. ETV fell from from 113 .+-. 8 ml during control to 59 .+-. 11 ml during E1 and to 29 .+-. 9 ml during E2 and rose to 136 .+-. 23 ml during recovery. There was no increase in extravascular lung water or mass determined gravimetrically at the end of the experiments. The thermal-dye technique will underestimate lung water in nonedematous lungs if emboli prevent complete diffusion of the thermal indicator.

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