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

In: Respiratory Failure

2 Oct 2014

Two reproducible measurements could not be obtained in two patients because of the disturbing influences of subcutaneous emphysema and edema on EIT measurements, and these were excluded from the analysis. The calculated CV was 4.1%, whereas the RC was 92%. A significant correlation of 0.91 (p < 0.001) between the analyses by both observers was found.
To assess the diagnostic performance of EIT in the ROC curve, an EVLW of 10 mL/kg was regarded as the reference because this value is regarded as the upper limit of normal. The obtained ROC curve (Fig 6) shows an area under the curve of 0.86 (p < 0.005), which indicates a good discriminating power of EIT for the assessment of EVLW. The sensitivity, specificity, and positive and negative predictive values were calculated for several cutoff points. At an IR of 0.60, a sensitivity for a supranor-mal EVLW of 100% was reached. The accompanying specificity and positive and negative predicted values are 53%, 67%, and 100%, respectively. When an IR of 0.64 was chosen as the cutoff level, the sensitivity was 93%, the specificity was 87%, and the positive and negative predicted values were 87% and 93%, respectively.

Respiratory Correlates
No significant correlation was found between the LIS and EVLW obtained by TDD. Also, the amount of EVLW was not significantly greater in the ARDS group (n = 8) in comparison with the ALI group (n = 6; 12.9 ± 6.5 vs 8.7 ± 7.5, respectively; p = 0.18). The IR showed no significant correlation with LIS, and also, there was no significant difference in the IR between the ARDS group and the ALI group (0.70 ± 0.15 vs 0.64 ± 0.17, respectively; p = 0.41). No significant correlation existed between PEEP and the EVLW obtained with TDD or the IR (r = 0.27, p = 0.35 and r = 0.20, p = 0.49, respectively). In the three patients in whom the influence of PEEP on the IR was examined by performing EIT measurements on the initial PEEP level and at zero PEEP, the difference in IRs at the different PEEP levels did not exceed 10% (Table 2).
Table 2—Differences in IR at Different PEEP Levels

Patient EVLW,mL/kg PEEP, cm H2O IR % Change in IR
1 NA 6 0.58
0 0.56 3.4
2 4.8 5 0.48
0 0.50 4.2
3 6.5 5 0.59
0 0.63 6.7

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