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

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 R 2 0.629–0.776 and R 2 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. Electronic supplementary material The online version of this article (10.1186/s13613-019-0560-5) contains supplementary material, which is available to authorized users.

Optimizing high-flow nasal cannula flow settings in adult hypoxemic patients based on peak inspiratory flow during tidal breathing

“…In two recently published studies in intubated patients, PTIF varied from 25–65 L/min [ 20 ] to 40–80 L/min [ 21 ], values that were higher than PTIF in our patients. This might be explained by the need to overcome the resistance of an endotracheal tube.…”

Regional peak flow as a novel approach to assess regional pulmonary mechanics by electrical impedance tomography: an observational validation study

“…Still, EIT comes with reoccurring limitations, such as regional mechanics using RPF-based regional relative impedance data instead of absolute flows as measured by the ventilator. Regional impedances and regional volumes are different physical concepts, but Mauri et al described high correlations between EIT-derived peak flow and spirometry-based peak flow, meaning that the RPF approach is physiologically valid in terms of using air flow for determining regional lung mechanic parameters ( 30 ). Also, impedance changes occurring distally from the electrode band to a lesser extent contribute to the generation of EIT images which may lead to the over- or underestimation of regional airflow at the plane of the electrode band ( 8 ).…”

Electrical Impedance Tomography in Acute Respiratory Distress Syndrome Management

“…When transitioning to spontaneous ventilation, EIT demonstrated that higher PEEP combined with lower pressure support smoothly redistributes V t from nondependent to dependent areas, improving the partial pressure of oxygen/fraction of inspired oxygen ratio and potentially diminishing focal stress (105, 106). Higher ΔP led to greater heterogeneity and basal collapse.…”