Flow-controlled ventilation maintains gas exchange and lung aeration in a pediatric model of healthy and injured lungs: A randomized cross-over experimental study

Abstract

Flow-controlled ventilation (FCV) is characterized by a constant flow to generate active inspiration and expiration. While the benefit of FCV on gas exchange has been demonstrated in preclinical and clinical studies with adults, the value of this modality for a pediatric population remains unknown. Thus, we aimed at observing the effects of FCV as compared to pressure-regulated volume control (PRVC) ventilation on lung mechanics, gas exchange and lung aeration before and after surfactant depletion in a pediatric model. Ten anesthetized piglets (10.4 ± 0.2 kg) were randomly assigned to start 1-h ventilation with FCV or PRVC before switching the ventilation modes for another hour. This sequence was repeated after inducing lung injury by bronchoalveolar lavage and injurious ventilation. The primary outcome was respiratory tissue elastance. Secondary outcomes included oxygenation index (PaO₂/FiO₂), PaCO₂, intrapulmonary shunt (Qs/Qt), airway resistance, respiratory tissue damping, end-expiratory lung volume, lung clearance index and lung aeration by chest electrical impedance tomography. Measurements were performed at the end of each protocol stage. Ventilation modality had no effect on any respiratory mechanical parameter. Adequate gas exchange was provided by FCV, similar to PRVC, with sufficient CO₂ elimination both in healthy and surfactant-depleted lungs (39.46 ± 7.2 mmHg and 46.2 ± 11.4 mmHg for FCV; 36.0 ± 4.1 and 39.5 ± 4.9 mmHg, for PRVC, respectively). Somewhat lower PaO₂/FiO₂ and higher Qs/Qt were observed in healthy and surfactant depleted lungs during FCV compared to PRVC (p < 0.05, for all). Compared to PRVC, lung aeration was significantly elevated, particularly in the ventral dependent zones during FCV (p < 0.05), but this difference was not evidenced in injured lungs. Somewhat lower oxygenation and higher shunt ratio was observed during FCV, nevertheless lung aeration improved and adequate gas exchange was ensured. Therefore, in the absence of major differences in respiratory mechanics and lung volumes, FCV may be considered as an alternative in ventilation therapy of pediatric patients with healthy and injured lungs.

Keywords: flow-controlled ventilation; gas exchange; lung aeration; pediatric model; respiratory distress syndrome; respiratory mechanics.

FIGURE 1

Study protocol. Schematic representation of the study protocol. FCV, flow-controlled ventilation mode; PRVC, pressure-regulated volume control ventilation mode; BG, arterial and venous blood sample collection and blood gas measurements; EIT, determination of lung aeration by electrical impedance tomography; FOT, measurement of respiratory mechanical parameters by forced oscillation technique; PiCCO, hemodynamical data collection by pulse index continuous cardiac output; EELV/LCI, measurement of end-expiratory lung volume and lung clearance index.

FIGURE 2

Gas exchange parameters. Gas exchange values during different ventilation stages in healthy and surfactant-depleted lungs. Empty bars represent healthy lung; patterned bars represent injured lung. *: p < 0.05 vs. same stage in healthy lung; #: p < 0.05 vs. BL within phase; $: p < 0.05 vs. FCV within phase. BL, baseline period; FCV, flow-controlled ventilation phase; PRVC, pressure-regulated volume control ventilation phase; PaO₂/FiO₂, fraction of inspired oxygen; Qs/Qt, intrapulmonary shunt fraction; PaCO₂, partial pressure of carbon dioxide in arterial blood.

FIGURE 3

End-expiratory lung volume and lung clearance index. Normalized end-expiratory lung volume and lung clearance index values during the different ventilation modalities for healthy and injured lungs. Empty bars represent healthy lung; patterned bars represent injured lung. *: p < 0.05 vs. same stage in healthy lung. BL, baseline period; FCV, flow-controlled ventilation phase; PRVC, pressure-regulated volume control ventilation phase; nEELV, end-expiratory lung volume normalized to bodyweight; LCI, lung clearance index.

FIGURE 4

Chest electrical impedance and aeration. Global absolute impedance values and regional relative contributions during different ventilation stages in healthy and surfactant-depleted lungs. The different colors represent the lung regions in supine position. Empty and color filled bars represent healthy lung; patterned bars represent injured lung. *: p < 0.05. BL, baseline period; FCV, flow-controlled ventilation phase; PRVC; AU, arbitrary unit.