Chest
Volume 106, Issue 5, November 1994, Pages 1517-1523
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Clinical Investigations in Critical Care
Effect of Bronchodilators on Lung Mechanics in the Acute Respiratory Distress Syndrome (ARDS)

https://doi.org/10.1378/chest.106.5.1517Get rights and content

The acute respiratory distress syndrome (ARDS) is a disorder of diffuse lung injury secondary to a wide variety of clinical insults (eg, sepsis) and is manifested by impaired oxygenation, pulmonary edema, and decreased static and dynamic compliance. More recently, airflow resistance has been shown to be increased in humans with ARDS. We designed a prospective, randomized, placebo-controlled, crossover trial to determine the presence and reversibility of increased airflow resistance in ARDS. We studied eight mechanically ventilated patients with ARDS (criteria: PaO2 ≤70 mm Hg with FIo2 ≤0.4; diffuse bilateral infiltrates; and pulmonary artery wedge pressure ≤18 mm Hg). Each was intubated with a No. 8.0 orotracheal tube. We measured dynamic compliance (Cdyn), static compliance (Cstat), airflow resistance across the lungs (RL), shunt fraction (Qs/Qt on FIO2=1.0), minute ventilation ( V˙E), PaO2/ PAO2, and dead space to tidal volume ratio (VD/VT). Patients were blindly assigned to receive either metaproterenol (1 mL 0.5% in 3 mL saline solution) or saline solution (4 mL) aerosolized over 15 min 6 h apart and in random order so that patients served as their own controls. Metaproterenol significantly reduced RL, peak and plateau airway pressure, and increased Cdyn. Metaproterenol tended to increase PaO2/PAO2, but had no effect on pulmonary shunt or dead space ventilation. We conclude that the increase in airflow resistance of ARDS is substantially reversed by aerosolized metaproterenol without affecting dead space. These data suggest that abnormalities of RL are at least partially due to bronchospasm.

Section snippets

Patient Selection

We studied eight patients who had ARDS and who were in the intensive care units of Vanderbilt University Medical Center. Patients who had an illness known to be associated with ARDS and who met all the following criteria were eligible for study: (1) arterial blood gases revealing a partial pressure of arterial oxygen of (PaO2) ≤70 mm Hg while they were breathing at least 40% oxygen or a ratio of partial pressure of arterial oxygen to partial pressure of alveolar oxygen (PaO2/PAO2) of ≤0.3

Results

Eight patients with ARDS from the intensive care units at Vanderbilt University Hospital were studied, including two men and six women with a mean age of 51 ± 7 years. Although two of the eight patients were smokers prior to hospitalization, neither had physical evidence, laboratory findings, or a history of previously existing lung disease. As Table 1 shows, physiologic variables were similar at the beginning of the metaproterenol and placebo portions of the trial, precluding a carryover

Discussion

Reduced lung or thoracic compliance, more specifically static compliance, is usually considered the primary disorder of lung mechanics in ARDS. The contribution of airflow resistance to lung mechanics and gas exchange abnormalities in ARDS had not been extensively studied until recently.12,13,30 In a previous study, we were able to show that resistance to airflow across the lung was significantly greater in 12 patients with ARDS than normal controls, 6.15 ± 0.08 vs 0.88 ± 0.08 H2O/L/s,

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    This work was supported by NHLBI grant HL-19153 (Special Center of Research in Pulmonary Diseases), HL-07123 (Training Grant), the Bernard Werthan Sr. Fund for Pulmonary Research, and a grant from Boerhinger-Ingleheim Inc.

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