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INTRODUCTION

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Obstructive airway disease is the most common chronic pulmonary pathology encountered in emergency medicine. Its most common etiology, asthma, is characterized by bronchoconstriction and airway hyper-responsiveness to certain stimuli. These stimuli trigger inflammatory mediators that lead to airway inflammation, mucosal edema, and, ultimately, reversible bronchospasm.1

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Conversely, chronic obstructive pulmonary disease (COPD) is a disorder characterized by abnormal tests of expiratory flow demonstrating air flow obstruction that becomes fixed and does not change markedly over a period of months. It is a multifocal pathology encompassing the triad of emphysema, chronic bronchitis, and asthma.2 The increasing prevalence and the large burden these disease entities impose on emergency medical care make the diagnosis and management of acute exacerbations vital to any health care provider.

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EPIDEMIOLOGY

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Approximately 25.9 million Americans had asthma in 2011, conferring an estimated financial burden of $56 billion in annual health care costs.3 In the United States, there are approximately 2 million emergency department (ED) visits per year for acute asthma, with 14 million people reporting having had asthma “attacks” in the past year.4 Approximately 2% to 20% of all ICU admissions are attributed to severe asthma, with intubation and mechanical ventilation necessary in up to one third of ICU admissions,5 with mortality rates in patients receiving intubation ranging from 10% to 20%.6

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COPD is the fourth most common cause of death in the United States, the third most common cause of hospitalization, and the only cause of death that is increasing in prevalence. The mortality of all patients while hospitalized for a COPD exacerbation is approximately 5% to 14%,7 while mortality of COPD patients admitted to an ICU for an exacerbation is 24%. For patients 65 years or older and discharged from the ICU after treatment of a COPD exacerbation, the 1-year mortality is 59%.7

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PATHOPHYSIOLOGY

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Asthma

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The Global Initiative for Asthma defines asthma as a heterogenous disease characterized by chronic airway inflammation. It is defined “by the history of respiratory symptoms such as wheeze, shortness of breath, chest tightness and cough that vary over time and in intensity, together with variable expiratory airflow limitation.” The variable airflow obstruction within the lung is often reversible, either spontaneously or with treatment. Exacerbations refer to the recurrent symptomatic flare-ups associated with this chronic disorder.8

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Asthma is characterized by airway inflammation with an abnormal accumulation of inflammatory mediators in response to various stimuli. Acutely, this accumulation leads to a reversible reduction of airway diameter caused by smooth muscle contraction, vascular congestion, bronchial wall edema, and thickened secretions.

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Chronic asthma can lead to airway remodeling, with subepithelial collagen deposition and increased airway resistance that manifests as a progressive decline in forced expiratory volume in 1 second (FEV1) measurements. After airway remodeling has occurred, the pathologic changes ...

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