Comparison of Two Aerosolized Bronchodilators in the Treatment of Severe Equine Chronic Obstructive Pulmonary Disease
Friday, Philippa Anne
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Aerosolized bronchodilator drugs are commonly used for treatment of horses with chronic obstructive pulmonary disease. Relative efficacy of sympathomimetic and parasympatholytic bronchodilators for relief of acute airway obstruction and improvement of pulmonary gas exchange was compared in 6 horses with COPD. Physical examination, arterial and venous blood gas analysis and measurement of end-tidal CO₂ tension were performed at time zero, 30 minutes, 1, 2, 3 and 4 hours after administration of aerosol ipratropium (0.35 μg/kg), albuterol (1 μg/kg) or placebo via an equine Aeromask and metered dose inhaler. Physiologic shunt fraction (QS/QT), alveolar dead space fraction (VD/VT) and alveolar to arterial oxygen tension difference (p(A-a)O₂) were calculated using standard formulas. At time zero, horses demonstrated severe respiratory compromise and marked alterations in pulmonary gas exchange, indicative of alveolar hypoventilation, VA/Q mismatching and diffusion impairment. Ipratropium treatment significantly (p< 0.05) reduced arterial CO₂ tension and end-tidal CO₂ tension toward normal, but significantly increased p(A-a)O₂ from baseline. The change in paCO₂ after ipratropium treatment was significantly different from albuterol and placebo treatment groups. There were no significant changes in response variables after albuterol and there were no treatment by time interactions. These results indicate that, under the conditions of this study, ipratropium (0.35 μg/kg) improved alveolar ventilation and had superior bronchodilator efficacy than albuterol (1 μg/kg) in horses with severe COPD. Marked impairment of pulmonary gas exchange persisted after bronchodilators, emphasizing that anti-inflammatory therapy and environmental control are also necessary for effective treatment of severe equine COPD.
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