Variation of poorly ventilated lung units (silent spaces) measured by electrical impedance tomography to dynamically assess recruitment

Savino Spadaro, Tommaso Mauri, Stephan H Böhm, Gaetano Scaramuzzo, Cecilia Turrini, Andreas D Waldmann, Riccardo Ragazzi, Antonio Pesenti, Carlo Alberto Volta, Savino Spadaro, Tommaso Mauri, Stephan H Böhm, Gaetano Scaramuzzo, Cecilia Turrini, Andreas D Waldmann, Riccardo Ragazzi, Antonio Pesenti, Carlo Alberto Volta

Abstract

Background: Assessing alveolar recruitment at different positive end-expiratory pressure (PEEP) levels is a major clinical and research interest because protective ventilation implies opening the lung without inducing overdistention. The pressure-volume (P-V) curve is a validated method of assessing recruitment but reflects global characteristics, and changes at the regional level may remain undetected. The aim of the present study was to compare, in intubated patients with acute hypoxemic respiratory failure (AHRF) and acute respiratory distress syndrome (ARDS), lung recruitment measured by P-V curve analysis, with dynamic changes in poorly ventilated units of the dorsal lung (dependent silent spaces [DSSs]) assessed by electrical impedance tomography (EIT). We hypothesized that DSSs might represent a dynamic bedside measure of recruitment.

Methods: We carried out a prospective interventional study of 14 patients with AHRF and ARDS admitted to the intensive care unit undergoing mechanical ventilation. Each patient underwent an incremental/decremental PEEP trial that included five consecutive phases: PEEP 5 and 10 cmH2O, recruitment maneuver + PEEP 15 cmH2O, then PEEP 10 and 5 cmH2O again. We measured, at the end of each phase, recruitment from previous PEEP using the P-V curve method, and changes in DSS were continuously monitored by EIT.

Results: PEEP changes induced alveolar recruitment as assessed by the P-V curve method and changes in the amount of DSS (p < 0.001). Recruited volume measured by the P-V curves significantly correlated with the change in DSS (rs = 0.734, p < 0.001). Regional compliance of the dependent lung increased significantly with rising PEEP (median PEEP 5 cmH2O = 11.9 [IQR 10.4-16.7] ml/cmH2O, PEEP 15 cmH2O = 19.1 [14.2-21.3] ml/cmH2O; p < 0.001), whereas regional compliance of the nondependent lung decreased from PEEP 5 cmH2O to PEEP 15 cmH2O (PEEP 5 cmH2O = 25.3 [21.3-30.4] ml/cmH2O, PEEP 15 cmH2O = 20.0 [16.6-22.8] ml/cmH2O; p <0.001). By increasing the PEEP level, the center of ventilation moved toward the dependent lung, returning to the nondependent lung during the decremental PEEP steps.

Conclusions: The variation of DSSs dynamically measured by EIT correlates well with lung recruitment measured using the P-V curve technique. EIT might provide useful information to titrate personalized PEEP.

Trial registration: ClinicalTrials.gov, NCT02907840 . Registered on 20 September 2016.

Keywords: Acute respiratory distress syndrome; Acute respiratory failure; Electrical impedance tomography; Personalized medicine; Positive end-expiratory pressure; Pressure-volume curve.

Conflict of interest statement

Ethics approval and consent to participate

The study was approved by the ethics committee of the Sant’Anna Hospital, Ferrara, Italy (protocol no. 141285), and registered with ClinicalTrials.gov (NCT02907840).

Consent for publication

Written informed consent was obtained from the patients or their relatives for publication of their individual details. The consent forms are held by the authors and are available for review by the Editor-in-Chief of this journal.

Competing interests

The authors declare that they have no competing interests.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures

Fig. 1
Fig. 1
Regional impedance map and “silent spaces” values during the different study phases in a representative patient. The impedance change maps (ΔZ) during the tidal breath are shown in the upper row for each step of the protocol; in the lower row, the corresponding level of silent spaces and center of ventilation are reported. Upon incrementally increasing positive end-expiratory pressure (PEEP), the percentage of dependent silent spaces decreased, whereas the opposite was true for decreasing PEEP levels
Fig. 2
Fig. 2
Correlation between dependent silent spaces and recruited lung volume assessed by pressure-volume (P-V) curve. The recruited volume determined by the shift in lung volumes between the P-V curves performed at different levels of positive end-expiratory pressure (PEEP) correlated inversely with the percentage change in dependent silent spaces. IBW Ideal body weight

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