Assessment of EVLW
Twenty-nine measurements in 14 patients could be performed. In two patients, no second day follow-up measurement could be performed due to damage to the fiberoptic catheter (patients 1 and 6); in one patient, it was impossible to collect correct EIT data due to the existence of severe subcutaneous edema (patient 7). Nine patients were monitored during 2 days; seven of them were monitored because EVLW was < 10 mL/kg, and two of them were monitored because of damage to the fiberoptic catheter. Patients 8 and 12 were measured during 5 and 3 days, respectively: patient 8 died, and the EVLW content in patient 12 reached 10 mL/kg.
At admission, the EVLW assessed by TDD was 11.2 ± 7.0 mL/kg, and the IR was 0.68 ± 0.15. As shown in Figure 2, bottom right, D, a significant correlation was found between the IR and the EVLW measured with TDD (r = 0.85; p < 0.001). To test the hypothesis that EIT is useful for assessing the amount of EVLW, the relation between the ventilation-induced impedance changes of the anterior part and those of the posterior part with the TDD EVLW was examined separately. The correlation between the ventilation-induced impedance change measured at the anterior part and EVLW was poor (r = — 0.40; p = 0.04; Fig 2, top right, B), whereas no correlation between the ventilation-induced impedance changes measured over both lungs (Fig 2, top left, A; r = 0.11; p = 0.57) or at the posterior part and EVLW existed (Fig 2, bottom left, C; r = — 0.27; p = 0.27). A significant correlation also existed between the changes in EVLW measured by TDD and EIT (r = 0.85; p < 0.005).
Figure 3 shows follow-up measurements at 2 consecutive days in 11 patients for TDD and EIT. In 3 of the 11 patients in whom repeated measurements of EVLW were made, TDD showed changes that were not seen with EIT (all in the normal range). Figure 4 depicts the curves of EIT and TDD for the monitoring of the EVLW content in patient 8 during 5 consecutive days. A similar course of the IR and TDD is shown. Figure 5 depicts a Bland-Altman plot to show the differences between the two repeated measurements of EIT against their means.
Figure 2. Scatter plots showing the relation between EIT and thermal dye dilution in the assessment of the amount of EVLW in both lungs (top left, A), the anterior part of the lungs (top right, B), and the posterior part of the lungs (bottom left, C); and the assessment of an IR in which both components are incorporated (bottom right, D).
Figure 3. Follow-up measurements of the first 2 consecutive days of the amount of EVLW obtained with thermal dye dilution and EIT. Each symbol reflects a patient.
Figure 4. The follow-up measurements during 5 days of patient 8 for thermal dye dilution and EIT.
Figure 5. Differences of repeated measurements vs the mean of both measurements show the reproducibility of EIT. Almost all measurements are within 2XSDs (dashed lines). The calculated CV and RC is 4.1% and 92%, respectively.
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