Evaluation of extravascular lung water by single thermal indicator

Much attention has been directed to developing early therapy that might prevent or ameliorate incipient adult respiratory distress syndrome (ARDS) before respiratory failure ensues. The relationship between increased extravascular lung water (EVLW) and pulmonary microvascular pressure has been used by numerous investigators to confirm alterations in the permeability of the alveolar capillary membrane. In the present study, EVLW was measured in 40 critically ill patients by an indicator dilution technique utilizing thermal indicator alone. Injection of cold saline distinguished intravascular and extravascular compartments with a sensitivity similar to that of the thermal-dye double-indicator dilution technique but without the withdrawal of blood, dye densitometry, or the preparation of special injectate. Both absolute volumes and volume changes over time measured by the single thermal indicator method compared favorably (p < .001) to EVLW values determined simultaneously by the conventional thermal-dye double-indicator dilution technique. These results suggest that the single thermal indicator technique may help identify the earliest phase of ARDS when fluid is starting to accumulate in the lung interstitium.