Evaluation of auto-regulated inspiratory support during rebreathing and acute lung injury in pigs.

BACKGROUND Auto-regulated inspiratory support mode (ARIS) is an original closed-loop pressure-support system that regulates the slope ("A") and the initial level ("B") of the applied inspiratory pressure, in order to achieve an optimal minute ventilation under constrained respiratory frequency, tidal volume, and maximum inspiratory airway pressure. The servo-controlled design results in a more or less decreasing applied pressure. OBJECTIVE The aim of this study was to evaluate the ARIS behavior, compared with pressure-support ventilation at a constant applied pressure. METHODS ARIS and pressure-support ventilation were randomly applied to 2 pig models of increasing ventilatory demand induced by a rebreathing test (n = 6), and of altered lung compliance induced by bronchoalveolar lavage (n = 6). The breathing pattern, work of breathing, and blood gas values were compared. ARIS automatically increased the mean inspiratory airway pressure in both groups. This increase was obtained in the rebreathing group by increasing "B" (35 +/- 3.5 cm H2O vs 42.8 +/- 2.5 cm H2O) and in the lung-injury group by decreasing the absolute value of "A" (25 +/- 5.5 cm H2O/s vs 14.7 +/- 8.6 cm H2O/s). RESULTS There were significant differences (p < 0.05) between ARIS and pressure-support ventilation. In the rebreathing group, tidal volume was 692 +/- 63 mL versus 606 +/- 96 mL, work of breathing was 1.17 +/- 0.45 J/L versus 1.44 +/- 0.27 J/L, and P(aCO2) was 54 +/- 9 mm Hg versus 63 +/- 7 mm Hg. In the lung-injury group, respiratory frequency was 25 +/- 4 breaths/min versus 42 +/- 10 breaths/min, tidal volume was 477 +/- 67 mL versus 300 +/- 63 mL, work of breathing was 0.54 +/- 0.3 J/L versus 0.99 +/- 0.45 J/L, and P(aCO2) was 36 +/- 8 mm Hg versus 53 +/- 15 mm Hg. CONCLUSIONS The ARIS servo control operates correctly, maintaining efficient ventilation facing an increase in respiratory demand or a decrease in respiratory system compliance.