Extravascular lung water to blood volume ratios as measures of permeability in sepsis-induced ALI/ARDS

Objective: We studied the relationship, and the effect of fluid loading on this, between the ratio of extravascular lung water (EVLW) to intrathoracic/pulmonary blood volumes (ITBV, PBV) and the radionuclide pulmonary leak index (PLI) to protein during sepsis-induced acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Design and setting: A prospective observational study, in the intensive care unit of a university hospital. Patients: Twenty-two consecutive mechanically ventilated patients with sepsis-related ALI/ARDS from pneumonia (n = 12) or extrapulmonary sources (n = 10), without elevated cardiac filling pressures. Intervention: Crystalloid (1700-1800 ml) or colloid (1000-1800 ml) fluid loading until target filling pressures. Measurements and results: Protein permeability was assessed noninvasively over the lungs with help of ⁶⁷Ga-labeled transferrin and ^99mTc-labeled red blood cells (Pulmonary leak index, upper limit normal 14.1 × 10^-3 /min) and EVLW and blood volumes by the thermal-dye transpulmonary dilution technique before and after fluid loading. Prior to fluids the pulmonary leak index related to the ratio of EVLW/ITBV and EVLW/PBV (r _s = 0.46) particularly when the pulmonary leak index was below 100 × 10^-3 /min and in extrapulmonary sepsis (PLI vs. EVLW/PBV r _s = 0.71). Fluid loading did not alter EVLW, EVLW/ITBV, or EVLW/PBV or the relationship to PLI. Conclusion: The data demonstrate that EVLW/ITBV or EVLW/PBV are imperfect measures of increased protein permeability in mechanically ventilated patients with sepsis-induced ALI/ARDS particularly when the PLI is severely increased and during pneumonia, independent of fluid status.