Effects of an Anticholinergic Bronchodilator on Arterial Blood Gases of Hypoxemic Patients with Chronic Obstructive Pulmonary Disease

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Abstract
Adrenergic bronchodilators have the potential drawback that they may increase hypoxemia in spite of relieving air-flow obstruction in patients with asthma. Anticholinergic bronchodilators are of interest as alternatives to beta-adrenergic agents, particularly in patients with chronic bronchitis and emphysema, yet little is known of the effects of either class of agent on gas exchange in patients with this diagnosis. We compared their effects on gas exchange in 12 patients with chronic bronchitis and emphysema who also had arterial hypoxemia in a double-blind crossover study. We found that nebulized atropine methonitrate, a quaternary ammonium anticholinergic bronchodilator, resulted in only minor and statistically insignificant effects on gas exchange at all times for as long as 60 min after its inhalation. In contrast, the beta-adrenergic bronchodilator metaproterenol hydrochloride resulted in a statistically significant decrease in the PaO2, the greatest mean decrease being 5.0 .+-. 2.5 mm Hg (mean .+-. 1 SD). The effects of metaproterenol hydrochloride resulted in a statistically significnat decrease in the PaO2, the greatest mean decrease being 5.0 .+-. 2.5 mm Hg (mean .+-. 1 SD). The effects of metaproterenol on arterial blood gases in this population of patients were more prolonged than those previously reported in asthmatic subjects with lesser degrees of hypoxemia. An anticholinergic bronchodilator might be preferable in patients with hypoxemia caused by chronic bronchitis and emphysema in that it does not carry the risk of worsening system hypoxemia.