Predictors of pulmonary edema formation during fluid loading in the critically ill with presumed hypovolemia

Objectives: It is largely unknown why extravascular lung water may increase during fluid loading in the critically ill with presumed hypovolemia. In this study we evaluated the hemodynamic predictors of such an increase. Design: A prospective observational study. Patients: Sixty-three presumed hypovolemic mechanically ventilated patients (22 septic and 41 nonseptic patients). Intervention: Fluid loading with saline or colloid fluids guided by (changes in) cardiac filling pressures. Measurements and Main Results: Before and after fluid-loading, hemodynamic and respiratory variables were recorded, including variables obtained by transpulmonary dilution such as cardiac index, pulmonary blood volume index, and extravascular lung water. Baseline parameters and change in parameters were compared between patients with a change in extravascular lung water <10% and patients with a change in extravascular lung water >= 10%. Predictive values for change in extravascular lung water >= 10% were evaluated. Baseline cardiac index and pulmonary blood volume index were higher, whereas change in cardiac index, change in pulmonary blood volume index, and change in Pao(2)/Fio(2) ratio were lower in patients with a change in extravascular lung water >= 10% than in patients with a change in extravascular lung water <10%. The change in extravascular lung water correlated to baseline cardiac index (r(2) = 0.17; p = .001), baseline pulmonary blood volume index (r(2) = 0.15; p = .001), change in pulmonary blood volume index (r(2) = 0.16; p < .001), and change in Pao(2)/Fio(2) ratio (r(2) = 0.13; p = .004). In multiple logistic regression analysis baseline cardiac index, baseline pulmonary blood volume index, the change in cardiac index, change in pulmonary blood volume index, and change in Pao(2)/Fio(2) ratio individually contributed to prediction of a change in extravascular lung water >= 10%, independent of the presence of sepsis, pulmonary vascular permeability, and cardiac filling pressures. A change in extravascular lung water >= 10% was predicted by baseline cardiac index (77% sensitivity, 98% specificity) and pulmonary blood volume index (92% sensitivity, 68% specificity), and by change in cardiac index (69% sensitivity, 59% specificity), change in pulmonary blood volume index (77% sensitivity, 82% specificity), and change in Pao(2)/Fio(2) ratio (77% sensitivity, 66% specificity). Conclusion: Extravascular lung water increase during fluid loading in the critically ill is predicted by a plateau of cardiac function and pulmonary vascular filling at baseline, rather than by pulmonary vascular permeability and filling pressures. Increasing extravascular lung water is further reflected by a decrease of Pao(2)/Fio(2) ratio. These observations may help preventing pulmonary fluid overloading. (Crit Care Med 2012; 40:793-799)