Different fresh gas flows produce similar rebreathing and regional ventilation during helmet continuous positive airway pressure in sedated Beagles.

Lower oxygen driving flows provide adequate CO2 washout during helmet CPAP in healthy sedated dogs without compromising ventilation.

This prospective experimental crossover study investigated the effects of four oxygen driving flows (5, 10, 15, and 20 L/min) on carbon dioxide rebreathing and regional ventilation in seven healthy adult Beagles receiving helmet continuous positive airway pressure (CPAP) via a Venturi valve system at approximately 5 cm H2O. Following stabilization at 15 L/min, dogs were evaluated at each flow rate in randomized order. Primary outcomes included inspired CO2 (PiCO2), PaCO2, and end-tidal CO2; secondary outcomes encompassed oxygenation indices, hemodynamics, and electrical impedance tomography-derived regional ventilation distribution. Although flow significantly affected PiCO2, the clinical magnitude was negligible — median PiCO2 differed by approximately 1 mm Hg between 5 and 15 L/min, with a maximum observed PiCO2 of only 2 mm Hg. No statistically significant differences were identified in PaCO2, end-tidal CO2, respiratory rate, surrogate minute ventilation, or regional ventilation distribution across flow conditions. Arterial oxygen tension varied among flows, but the P:F ratio remained unchanged, suggesting comparable oxygenation efficiency regardless of flow setting. These findings indicate that CO2 rebreathing during helmet CPAP remains clinically minimal across the tested driving flows and does not produce measurable alterations in arterial CO2 or ventilation patterns. Clinically, lower oxygen driving flows may provide sufficient helmet washout in healthy sedated dogs using a Venturi-based system, potentially reducing oxygen consumption without compromising patient safety or ventilatory adequacy.

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