Noninvasive assessment of airflows by electrical impedance tomography in intubated hypoxemic patients: an exploratory study

Tommaso Mauri, Elena Spinelli, Francesca Dalla Corte, Eleonora Scotti, Cecilia Turrini, Marta Lazzeri, Laura Alban, Marco Albanese, Donatella Tortolani, Yu-Mei Wang, Savino Spadaro, Jian-Xin Zhou, Antonio Pesenti, Giacomo Grasselli, Tommaso Mauri, Elena Spinelli, Francesca Dalla Corte, Eleonora Scotti, Cecilia Turrini, Marta Lazzeri, Laura Alban, Marco Albanese, Donatella Tortolani, Yu-Mei Wang, Savino Spadaro, Jian-Xin Zhou, Antonio Pesenti, Giacomo Grasselli

Abstract

Background: Noninvasive monitoring of maximal inspiratory and expiratory flows (MIF and MEF, respectively) by electrical impedance tomography (EIT) might enable early recognition of changes in the mechanical properties of the respiratory system due to new conditions or in response to treatments. We aimed to validate EIT-based measures of MIF and MEF against spirometry in intubated hypoxemic patients during controlled ventilation and spontaneous breathing. Moreover, regional distribution of maximal airflows might interact with lung pathology and increase the risk of additional ventilation injury. Thus, we also aimed to describe the effects of mechanical ventilation settings on regional MIF and MEF.

Methods: We performed a new analysis of data from two prospective, randomized, crossover studies. We included intubated patients admitted to the intensive care unit with acute hypoxemic respiratory failure (AHRF) and acute respiratory distress syndrome (ARDS) undergoing pressure support ventilation (PSV, n = 10) and volume-controlled ventilation (VCV, n = 20). We measured MIF and MEF by spirometry and EIT during six different combinations of ventilation settings: higher vs. lower support during PSV and higher vs. lower positive end-expiratory pressure (PEEP) during both PSV and VCV. Regional airflows were assessed by EIT in dependent and non-dependent lung regions, too.

Results: MIF and MEF measured by EIT were tightly correlated with those measured by spirometry during all conditions (range of R2 0.629-0.776 and R2 0.606-0.772, respectively, p < 0.05 for all), with clinically acceptable limits of agreement. Higher PEEP significantly improved homogeneity in the regional distribution of MIF and MEF during volume-controlled ventilation, by increasing airflows in the dependent lung regions and lowering them in the non-dependent ones.

Conclusions: EIT provides accurate noninvasive monitoring of MIF and MEF. The present study also generates the hypothesis that EIT could guide PSV and PEEP settings aimed to increase homogeneity of distending and deflating regional airflows.

Keywords: Acute respiratory distress syndrome; Electrical impedance; Mechanical ventilation; Respiratory airflow; Respiratory failure; Spirometry.

Conflict of interest statement

Dr Mauri received personal fees as speaker from Drager, outside the submitted work. Dr. Grasselli received funding for lectures from Getinge, Draeger Medical, Fisher & Paykel, Pfizerand and travel/accommodation/congress registration support from Biotest and Getinge. The remaining authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Airflow waveforms measured by spirometer (red line) and electrical impedance tomography (EIT) (blue line) in two representative patients during pressure support ventilation (left) and volume-controlled ventilation (right). Note the correspondence between peak values by the two methods, with only modest underestimation by EIT
Fig. 2
Fig. 2
Correlations and Bland–Altman plots of airflows measured by spirometer and electrical impedance tomography (EIT). Top panels (a, b) show data for maximal inspiratory flow (MIF), while bottom panels (c, d) for maximal expiratory flow (MEF)
Fig. 3
Fig. 3
Lower levels of pressure support improved homogeneity of regional maximal flow distribution both during inspiration and expiration in comparison with higher support (PSVlow vs. PSVhigh) (a); higher positive end-expiratory pressure level led to an improvement in maximal inspiratory and expiratory flows (MIF and MEF) homogeneity both during pressure support ventilation (PSV-PEEPhigh vs. PSV-PEEPlow) (b) and volume-controlled ventilation (VCV-PEEPhigh vs. VCV-PEEPlow); (c) dashed line represents perfect homogeneity

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