Electrical impedance tomography in the assessment of extravascular lung water in noncardiogenic acute respiratory failure

Study objectives: To establish the value of electrical impedance tomography (EIT) in assessing pulmonary edema in noncardiogenic acute respiratory fai lure (ARF), as compared to the thermal dye double indicator dilution techni que (TDD), Design: Prospective clinical study. Setting: ICU of a general hospital. Patients: Fourteen ARF patients. Interventions: In order to use the TDD to determine the amount of extravascular lung water (EVLW), a fiberoptic cathe ter was placed in the femoral artery. Measurements and main results: Fourteen consecutive ARF patients receiving mechanical ventilation were measured by EIT and TDD. EIT visualizes the imp edance changes caused by the ventilation in two-dimensional image planes. A n impedance ratio (IR) of the ventilation-induced impedance changes of a po sterior and an anterior part of the lungs was used to indicate the amount o f EVLW. For the 29 measurements in 14 patients, a significant correlation b etween EIT and TDD (r = 0.85; p < 0.001) was found. The EIT reproducibility was good. The diagnostic value of the method was tested by receiver operat or characteristic analysis, with 10 mL/kg of EVLW considered as the upper l imit of normal. At a cutoff level of the LR of 0.64, the IR had a sensitivi ty of 93%, a specificity of 87%, and a positive predictive value of 87% for a supranormal amount of EVLW, Follow-up measurements cr ere performed in 1 1 patients. A significant correlation was found between the changes in EVLW measured with EIT and TDD (r = 0.85; p < 0.005), Conclusion: We conclude that EIT is a noninvasive technique for reasonably estimating the amount of EVLW in noncardiogenic ARF.