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CRITICAL CARE AND TRAUMA

Ventilation Strategies in the Obstructed Airway in a Bench Model Simulating a Nonintubated Respiratory Arrest Patient

From the Department of Anesthesiology and Critical Care Medicine, Innsbruck Medical University, Innsbruck, Austria.

Address correspondence and reprint requests to Dr. Holger Herff, Department of Anesthesiology and Critical Care Medicine, Innsbruck Medical University, Anichstrasse 35, 6020 Innsbruck, Austria. Address e-mail to holger.herff{at}i-med.ac.at.

BACKGROUND: The Smart Bag MO® is an adult flow-limited bag-valve device designed to reduce the risk of stomach inflation in an unprotected airway. Its properties in severe airway obstruction are as yet unknown.

METHODS: In a bench model, we evaluated respiratory mechanics and delivered tidal volumes although ventilating at airway resistances of 4, 10, and 20 cm H₂O · L^–1 · s^–1 once with a flow-limited bag-valve device and once with a standard bag-valve device to simulate a respiratory arrest patient with an unprotected airway.

RESULTS: Inspiratory times were always longer with the flow-limited bag-valve device than with the standard bag-valve device. Lung tidal volume in the simulated unobstructed airway was 750 ± 70 mL using the flow-limited bag-valve device versus 780 ± 30 mL using the standard bag-valve device (n.s.); in the simulated medium obstructed airway it was 800 ± 70 versus 850 ± 20 mL (n.s.), and in the simulated severely obstructed airway it was 210 ± 20 versus 170 ± 10 mL (P < 0.01). Peak airway pressure in the simulated unobstructed airway was 15 ± 2 cm H₂O using the flow-limited bag-valve device versus 22 ± 4 cm H₂O using the standard bag-valve device (P < 0.01); in the simulated medium obstructed airway it was 22 ± 1 versus 39 ± 7 cm H₂O (P < 0.01), and in the simulated severely obstructed airway it was 26 ± 1 versus 61 ± 3 cm H₂O (P < 0.01). Stomach inflation in the simulated unobstructed airway was 0 mL/min using both bag-valve devices; in the simulated medium obstructed airway it was 0 mL/min for the flow-limited bag-valve device versus 200 ± 20 mL/min for the standard bag-valve device (P < 0.01), and in the simulated severely obstructed airway it was 0 versus 1240 ± 50 mL/min (P < 0.01).

CONCLUSION: In a simulated severely obstructed unprotected airway, the use of a flow-limited bag-valve device resulted in longer inspiratory times, higher tidal volumes, lower inspiratory pressures, and no stomach inflation compared with a standard bag-valve device.