Electrical Impedance Tomography in the Assessment of Extravascular Lung Water in Noncardiogenic Acute Respiratory Failure: Statistical Analysis

In: Respiratory Failure

29 Sep 2014

Electrical Impedance Tomography in the Assessment of Extravascular Lung Water in Noncardiogenic Acute Respiratory Failure: Statistical AnalysisTDD: In this study, TDD assessment of the amount of EVLW was performed using the COLD System (Pulsion Medical Systems; Munich, Germany). The principle is based on the injection of two indicators (indocyanine green [ICG] and cold glucose 5% [4°C]), with detection of their dilution curves after passage through the pulmonary circulation. The ICG and glucose (10 to 12 mL; 1 mg ICG was dissolved in 1 mL glucose 5%) are administered in the right atrium and detected in the femoral artery. ICG is protein-bound and therefore confined to the intravascular space. The thermal indicator distributes in the extravascular compartment. Source
A specially designed thermistor-tipped fiberoptic catheter (Pulsion type) was used to detect both indicators in the femoral artery. In this way, the dye concentration is measured in vivo. The difference in area under the indicator dilution curves yields the volume outside the pulmonary capillaries, which is the volume of the EVLW. The EVlW is expressed in mL/kg body weight. Normal values range from 5 to 10 mL/kg. Patients are expected to have mild edema when the values range from 10 to 20 mL/kg, and they are expected to have severe pulmonary edema when values are > 20 mL/kg.
Statistical Analysis
Data are presented as mean ± SD. In order to depict the relationship between the IR and the values of EVLW obtained with TDD, linear regression analysis was used. The mean and SD of the differences between two consecutive EIT measurements were calculated and plotted against the mean values in order to visualize reproducibility. Furthermore, the coefficient of variation (CV) and the reliability coefficient (RC) between both measurements were calculated: CV is the SD of the difference within the repeated measurements divided by the mean of both measurements, whereas the RC is the variance of repeated measurements divided by the variance between repeated measurements and the variance of the difference within the repeated measurements.


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