Electrical impedance tomography (EIT) has undergone 30 years of development. Functional chest examinations with this technology are considered clinically relevant, especially for monitoring regional ...lung ventilation in mechanically ventilated patients and for regional pulmonary function testing in patients with chronic lung diseases. As EIT becomes an established medical technology, it requires consensus examination, nomenclature, data analysis and interpretation schemes. Such consensus is needed to compare, understand and reproduce study findings from and among different research groups, to enable large clinical trials and, ultimately, routine clinical use. Recommendations of how EIT findings can be applied to generate diagnoses and impact clinical decision-making and therapy planning are required. This consensus paper was prepared by an international working group, collaborating on the clinical promotion of EIT called TRanslational EIT developmeNt stuDy group. It addresses the stated needs by providing (1) a new classification of core processes involved in chest EIT examinations and data analysis, (2) focus on clinical applications with structured reviews and outlooks (separately for adult and neonatal/paediatric patients), (3) a structured framework to categorise and understand the relationships among analysis approaches and their clinical roles, (4) consensus, unified terminology with clinical user-friendly definitions and explanations, (5) a review of all major work in thoracic EIT and (6) recommendations for future development (193 pages of online supplements systematically linked with the chief sections of the main document). We expect this information to be useful for clinicians and researchers working with EIT, as well as for industry producers of this technology.
Cardiac surgery produces dorso-basal atelectasis and ventilation/perfusion mismatch, associated with infection and prolonged intensive care. A postoperative lung volume recruitment manoeuvre to ...decrease the degree of atelectasis is routine. In patients with severe respiratory failure, prone positioning and recruitment manoeuvres may increase survival, oxygenation, or both. We compared the effects of lung recruitment in prone vs supine positions on dorsal inspiratory and end-expiratory lung aeration.
In a prospective RCT, 30 post-cardiac surgery patients were randomly allocated to recruitment manoeuvres in the prone (n=15) or supine position (n=15). The primary endpoints were late dorsal inspiratory volume (arbitrary units a.u.) and left/right dorsal end-expiratory lung volume change (a.u.), prone vs supine after extubation, measured using electrical impedance tomography. Secondary outcomes included left/right dorsal inspiratory volumes (a.u.) and left/right dorsal end-expiratory lung volume change (a.u.) after prone recruitment and extubation.
The last part of dorsal end-inspiratory volume after extubation was higher after prone (49.1 a.u.; 95% confidence interval CI, 37.4–60.6) vs supine recruitment (24.2 a.u.; 95% CI, 18.4–29.6; P=0.024). Improvement in left dorsal end-expiratory lung volume after extubation was higher after prone (382 a.u.; 95% CI, 261–502) vs supine recruitment (–71 a.u., 95% CI, –140 to –2; n=15; P<0.001). After prone recruitment, left vs right predominant end-expiratory dorsal lung volume change disappeared after extubation. However, both left and right end-expiratory volumes were higher in the prone group, after extubation.
Recruitment in the prone position improves dorsal inspiratory and end-expiratory lung volumes after cardiac surgery.
NCT03009331.
Purpose
The optimal method for estimating transpulmonary pressure (i.e. the fraction of the airway pressure transmitted to the lung) has not yet been established.
Methods
In this study on 44 patients ...with acute respiratory distress syndrome (ARDS), we computed the end-inspiratory transpulmonary pressure as the change in airway and esophageal pressure from end-inspiration to atmospheric pressure (i.e. release derived) and as the product of the end-inspiratory airway pressure and the ratio of lung to respiratory system elastance (i.e. elastance derived). The end-expiratory transpulmonary pressure was estimated as the product of positive end-expiratory pressure (PEEP) minus the direct measurement of esophageal pressure and by the release method.
Results
The mean elastance- and release-derived transpulmonary pressure were 14.4 ± 3.7 and 14.4 ± 3.8 cmH
2
O at 5 cmH
2
O of PEEP and 21.8 ± 5.1 and 21.8 ± 4.9 cmH
2
O at 15 cmH
2
O of PEEP, respectively (
P
= 0.32,
P
= 0.98, respectively), indicating that these parameters were significantly related (
r
2
= 0.98,
P
< 0.001 at 5 cmH
2
O of PEEP;
r
2
= 0.93,
P
< 0.001 at 15 cmH
2
O of PEEP). The percentage error was 5.6 and 12.0 %, respectively. The mean directly measured and release-derived transpulmonary pressure were −8.0 ± 3.8 and 3.9 ± 0.9 cmH
2
O at 5 cmH
2
O of PEEP and −1.2 ± 3.2 and 10.6 ± 2.2 cmH
2
O at 15 cmH
2
O of PEEP, respectively, indicating that these parameters were not related (
r
2
= 0.07,
P
= 0.08 at 5 cmH
2
O of PEEP;
r
2
= 0.10,
P
= 0.53 at 15 cmH
2
O of PEEP).
Conclusions
Based on our observations, elastance-derived transpulmonary pressure can be considered to be an adequate surrogate of the release-derived transpulmonary pressure, while the release-derived and directly measured end-expiratory transpulmonary pressure are not related.
To assess lung volume and compliance changes during open- and closed-system suctioning using electric impedance tomography (EIT) during volume- or pressure-controlled ventilation.
Experimental study ...in a university research laboratory.
Nine bronchoalveolar saline-lavaged pigs.
Open and closed suctioning using a 14-F catheter in volume- or pressure-controlled ventilation at tidal volume 10 ml/kg, respiratory rate 20 breaths/min, and positive end-expiratory pressure 10 cmH2O.
Lung volume was monitored by EIT and a modified N2 washout/-in technique. Airway pressure was measured via a pressure line in the endotracheal tube. In four ventral-to-dorsal regions of interest regional ventilation and compliance were calculated at baseline and 30 s and 1, 2, and 10 min after suctioning. Blood gases were followed. At disconnection functional residual capacity (FRC) decreased by 58+/-24% of baseline and by a further 22+/-10% during open suctioning. Arterial oxygen tension decreased to 59+/-14% of baseline value 1 min after open suctioning. Regional compliance deteriorated most in the dorsal parts of the lung. Restitution of lung volume and compliance was significantly slower during pressure-controlled than volume-controlled ventilation.
EIT can be used to monitor rapid lung volume changes. The two dorsal regions of the lavaged lungs are most affected by disconnection and suctioning with marked decreases in compliance. Volume-controlled ventilation can be used to rapidly restitute lung aeration and oxygenation after lung collapse induced by open suctioning.
We developed a modified nitrogen washin/washout technique based on standard monitors using inspiratory and end-tidal gas concentration values for functional residual capacity (FRC) measurements in ...patients with acute respiratory failure (ARF). For validation we used an oxygen-consuming lung model ventilated with an inspiratory oxygen fraction (Fio2) between 0.3 and 1.0. The respiratory quotient of the lung model was varied between 0.7 and 1.0. Measurements were performed changing Fio2 with fractions of 0.1, 0.2, and 0.3. In 28 patients with ARF, duplicate measurements were performed. In the lung model, an Fio2 change of 0.1 resulted in a value of 103 ± 5% of the reference FRC value of the lung model, and the precision was equally good up to an Fio2 of 1.0 with a value of 103 ± 7%. In the patients, duplicate measurements showed a bias of −5 mL with a 95% confidence interval −38; 29 mL . A comparison of a change in Fio2 of 0.1 with 0.3 showed a bias of −9 mL and limits of agreement of −365; 347 mL. This study shows good precision of FRC measurements with standard monitors using a change in Fio2 of only 0.1. Measurements can be performed with equal precision up to an Fio2 of 1.0.
. Protective ventilation should be based on
mechanics and transpulmonary driving pressure (ΔPTP), as this 'hits' the lung directly.
. The change in end-expiratory lung volume (ΔEELV) is determined by ...the size of the PEEP step and the elastic properties of the lung (EL), ΔEELV/ΔPEEP. Consequently, EL can be determined as ΔPEEP/ΔEELV. By calibration of tidal inspiratory impedance change with ventilator inspiratory tidal volume, end-expiratory lung impedance changes were converted to volume changes and lung P/V curves were obtained during a PEEP trial in ten patients with acute respiratory failure. The PEEP level where ΔPTP was lowest (optimal PEEP) was determined as the steepest point of the lung P/V curve.
. Over-all EL ranged between 7.0-23.2 cmH
O/L. Optimal PEEP was 12.9 cmH
O (10-16) with ΔPTP of 4.1 cmH
O (2.8-7.6). Patients with highest EL were PEEP non-responders, where EL increased in non-dependent and dependent lung at high PEEP, indicating over-distension in all lung. Patients with lower EL were PEEP responders with decreasing EL in dependent lung when increasing PEEP.
. PEEP non-responders could be identified by regional lung P/V curves derived from ventilator calibrated EIT. Optimal PEEP could be determined from the equation for the lung P/V curve.
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