Effects of 2 modes of positive pressure ventilation on respiratory mechanics and gas exchange in foals

Abstract

Background: Continuous positive airway pressure (CPAP) and pressure support ventilation (PSV) can improve respiratory mechanics and gas exchange, but different airway pressures have not been compared in foals. Hypothesis/Objectives: Assess the effect of different airway pressures during CPAP and PSV have on respiratory function in healthy foals with pharmacologically induced respiratory insufficiency. We hypothesized that increased airway pressures would improve respiratory mechanics and increased positive end-expiratory pressure (PEEP) would be associated with hypercapnia. Animals: Six healthy foals from a university teaching herd. Methods: A prospective, 2-phase, 2-treatment, randomized cross-over study design was used to evaluate sequential interventions in sedated foals using 2 protocols (CPAP and PSV). Outcome measures included arterial blood gases, spirometry, volumetric capnography, lung volume and aeration assessed using computed tomography (CT). Results: Sedation and dorsal recumbency were associated with significant reductions in arterial oxygen pressure (PaO2), respiratory rate, and tidal volume. Continuous positive airway pressure was associated with improved PaO2, without concurrent hypercapnia. Volumetric capnography identified improved ventilation:perfusion (V/Q) matching and increased carbon dioxide elimination during ventilation, and spirometry identified decreased respiratory rate and increased tidal volume. Peak inspiratory pressure was moderately associated with PaO2 and lung volume. Improved pulmonary aeration was evident in CT images, and lung volume was increased, particularly during CPAP. Conclusions and Clinical Importance: Both CPAP and PSV improved lung mechanics and gas exchange in healthy foals with induced respiratory insufficiency.