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

In: Respiratory Failure

4 Oct 2014

The lack of significant correlation between PEEP and the IR, and the fact that in three patients, despite the change in PEEP (although small) and an unchanged EVLW, the IR remained within a 10% change, prove the independency of the IR in relation to the PEEP. Second, pleural effusion interfered with transthoracic impedance measurements of EVLW. Because the presence of EVLW by EIT is determined by the gas inflation differences, pleural effusion will not interfere. Third, because EIT uses an electrical current, circumstances that influence conductivities of tissue might disturb the assessment of accurate EIT-data (ie, subcutaneous edema and subcutaneous emphysema). In this study, nine patients suffered from subcutaneous edema, but the latter prevented meaningful data collection in only one patient. Finally, because the IR is based on gas inflation differences, diseases that alter the distribution of ventilation (emphysema, lung cancer, or pneumonectomy) might disturb the interpretation of the IR as an indication of the presence of EVLW. No patient in our study was known to suffer from any of these coincidental diseases; as a result, their effect remains unknown. canadian family pharmacy

In our study, no correlation between the EVLW content, as determined by TDD or the IR, and the LIS was found. Based on this result, EIT and TDD may not be used to judge the severity of ARF, although the literature shows that the EVLW content can serve as a tool to judge the severity of ARF. Also, the clinical benefit of measuring EVLW in patients with ARF is controversial. Whereas some authors have showed that pulmonary edema may have prognostic importance and that reducing pulmonary edema may improve out-come, others have not been able to demonstrate an association between EVLW and outcome in ARF.” Despite these limitations, the use of EIT to assess the amount of EVLW might still be desirable for several reasons. First, EIT was compared to an invasive “gold standard.” Although we know that TDD has its limitations (ie, underestimation in patients with intravascular pulmonary shunts), it is a technique that has a very good correlation with gravimetric techniques and is clinically available. In this clinical study, EIT showed good results compared to TDD and, therefore, is promising. A study in which EIT is compared to gravimetric techniques is still necessary. Second, because TDD is invasive and expensive, no good follow-up studies for clinical outcome are possible. EIT is inexpensive and non-invasive, thereby allowing for the opportunity to do more research that will end the controversy over EVLW and outcome in literature.
In conclusion, the present study shows that EIT is a noninvasive technique that may be used to reasonably estimate the presence of EVLW in ARF if the IR based on ventilation-induced impedance changes between the posterior and anterior part of the lung is applied.

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