Ventilation-perfusion response after fenoterol in hypoxemic patients with stable COPD

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From: Chest(Vol. 110, Issue 1)
Publisher: Elsevier B.V.
Document Type: Article
Length: 3,930 words

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Background: The effects of vasoactive drugs, including bronchodilators, on vascular and pulmonary dynamics are interrelated, complex and difficult to measure, but important because of potential deleterious effects on gas exchange. Methods: To assess the effects of fenoterol at both high and low dose on pulmonary gas exchange in 24 hypoxemic patients with stable COPD: fenoterol, 5 ma; fenoterol, 1 mg and ipratropium bromide, 0.5 ma; ipratropium bromide, 0.5 ma; or matched placebo were nebulized in a double-blind, placebo-controlled fashion. Spirometry, ventilation, systemic hemodynamics, and respiratory and inert gases were measured before and 15, 60, and 120 min after each treatment. Results: Compared with placebo, heart rate (p<0.002) and cardiac output (p=0.05) increased after high-dose fenoterol therapy to return to baseline values by 120 min. Following fenoterol at high dose, mean maximum Pa [O.sub.2] change from baseline decreased by 6.3 [+ or -]1.1 mm Hg (SD) and both alveolararterial oxygen pressure difference (P [A-a] [O.sub.2]), by 8.3 [+ or -]4.0 mm Hg, and ventilation-perfusion (VA/Q) mismatching increased, as evidenced by increments of the dispersion of pulmonary blood flow, without reaching significance; likewise, low-dose fenoterol therapy increased VA/Q inequalities while both Pa [O.sub.2] and P(A-a) [O.sub.2] remained unchanged. Conclusions: In this population of COPD patients, high-dose fenoterol therapy did not significantly increase heart rate and cardiac output resulting in minor adverse consequences on arterial oxygenation and VA/Q relationships. (CHEST 1996; 110:71-77)

Key words: anticholinergics; [beta]-agonists; chronic airflow obstruction; gas exchange abnormalities; multiple inert gas elimination technique

Abbreviations: [Do.sub.2]=oxygen delivery; f=respiratory frequency; HR=heart rate; MlGET=multiple inert gas elimination technique; P(A-a) [O.sub.2]=alveolar-arterial oxygen gradient; PS=systemic arterial pressure; QT=cardiac output;VA/Q=ventilation-perfusion; VE=minute ventilation; V [O.sub.2]=oxygen consumption

In recent years, there has been an increased interest in the unwanted effects of fenoterol, because with the doses used in clinical practice this [beta]-agonist can cause more cardiac and systemic side effects than salbutamol and terbutaline.[1,2] The undesirable side effects of fenoterol may aggravate pulmonary gas exchange abnormalities due to increased cardiac output (QT) release of hypoxic pulmonary vasoconstriction and/or increased oxygen consumption ([Vo.sub.2]).[34]

To date and to our knowledge, no direct evidence is available concerning ventilation-perfusion (VA/Q) inequalities and the influence of extrapulmonary factors regulating pulmonary gas exchange, more specifically QT, after administration of fenoterol in patients with COPD. The present study was aimed to assess the short-term effects of nebulized fenoterol on pulmonary gas exchange in hypoxemic patients with stable COPD using the multiple inert gas elimination technique (MIGET).[44] The inert gas approach provides a quantum leap forward in our comprehension of gas exchange by giving a more robust information regarding the role of VAIQ mismatch and its interaction with the extrapulmonary determinants of gas exchange than previously available tools.[3,4] Likewise, we wondered whether dose-response differences could be found following nebulization of this selective [beta]-agonist. To do so, we also compared fenoterol given singly, at a high dose, with a low dose of the drug administered in combination with ipratropium to confer a similar bronchodilator effect.

MATERIALS AND METHODS

Patients

Twenty-four patients with moderate to severe COPD'...

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Gale Document Number: GALE|A18554240