Chronic Obstructive Pulmonary Disease

David S. Howes and Leah W. Skjei

Chronic obstructive pulmonary disease (COPD) comprises a spectrum of chronic respiratory illnesses characterized by cough, sputum production, dyspnea, airflow limitation, impaired gas exchange, and inflammation (1–3). The mortality rate is greater than 50% within 10 years of diagnosis. COPD is the fourth leading cause of death in the United States and is expected to become the third leading cause of death worldwide by 2020 (4). The overall prevalence of symptomatic COPD in selected countries is 10.1% (5).

The term COPD includes conditions, other than asthma, that have the common feature of airflow obstruction and inflammation of the small airways and alveoli. The inflammatory response in COPD is different than that seen in asthma and involves the recruitment of neutrophils, macrophages, and cytotoxic T lymphocytes. Inflammation of the small airways leads to airway wall thickening and fibrosis, resulting in decreased airway diameter and increased resistance to flow. This is chronic obstructive bronchitis (1,6). Chronic bronchitis is characterized clinically by a productive cough caused by excessive production of bronchial mucus that must be present for 3 months in a year in at least 2 successive years. Pulmonary emphysema, in contrast, is defined from a pathologic standpoint by inflammatory infiltrates in the alveolar wall, leading to an irreversible enlargement of the alveolar air spaces with destruction of the alveolar wall and pulmonary capillary bed (1,6). The result is a reduction in the elastic pressure that generates expiratory flow (6). Most patients with COPD will have remodeling of both their small airways and their alveoli due to abnormal inflammation, and will therefore exhibit characteristics of both chronic bronchitis and emphysema.

The predominant risk factor for COPD is tobacco use; half of smokers develop airflow obstruction (4). However, 5% to 10% of patients with COPD have never smoked, implicating other causal factors (1). Other risk factors include inhalation of organic and inorganic dusts and fumes, that is environmental pollution, passive smoke inhalation, and occupational exposure (7). α₁-Antitrypsin deficiency is a genetic risk factor and is present in 1% to 2% of patients with COPD (4). Regardless of etiology, the ultimate outcome is irreversible airflow limitation.

The natural course of COPD is one of progressively worsening dyspnea, hypoxemia, and diminished exercise tolerance, with recurrent exacerbations. Most patients with COPD have modest reversible airway obstruction. Although the forced expiratory volume in 1 second (FEV₁) is classically considered the best single prognostic indicator of disability and death, disease severity is better assessed by considering FEV₁, body mass index (BMI), and exercise performance (3). The onset of chronic hypoxemia leads to progressive clinical deterioration caused by cor pulmonale, which worsens already diminished lung function. Recurrent episodes of infection and respiratory failure ultimately result in death. Long-term ambulatory oxygen therapy prolongs life in patients with advanced COPD.

CLINICAL PRESENTATION

All patients with COPD exhibit airflow obstruction, but the pure forms of emphysema and chronic bronchitis have distinctive clinical features. Patients with emphysema tend to hyperventilate to compensate for the decreased ability of the lungs to oxygenate the blood due to their decreased alveolar surface area. These classic “pink puffers” work hard to establish a near-normal partial pressure of arterial oxygen (PaO₂), and they appear barrel-chested, dyspneic, and tachypneic. They use pursed lips breathing to create positive end-expiratory pressure (PEEP) to prevent early airway closure. Breath sounds are markedly diminished, with a prolonged expiratory phase.

In contrast, patients with chronic bronchitis tolerate hypoxemia well and make no effort to hyperventilate. Chronic hypoxia induces a secondary polycythemia that, combined with the cyanosis of marked desaturation of hemoglobin, produces a plethoric appearance. These patients tolerate an elevated partial pressure of arterial carbon dioxide (PaCO₂) and have a less labored respiratory pattern. With the decreased work of breathing, the patient with chronic bronchitis does not experience muscle wasting like the emphysematous patient. These features produce the picture of the “blue bloater.” Lung examination reveals rhonchi, rales, and variable wheezing. The severity of COPD as classified by Global Initiative for Chronic Lung Disease (GOLD) is listed in Table 77.1 (8).

Most patients who present with an acute exacerbation of COPD do not fit either picture precisely. Patients with COPD exacerbation present with worsening of baseline dyspnea, cough, and/or sputum that is beyond normal day-to-day variations, is acute in onset, and may warrant a change in regular medication (8). Physical examination may reveal a variable degree of respiratory distress, tachypnea, accessory muscle use, retractions, and cyanosis. On auscultation, one may hear diminished breath sounds, a prolonged expiratory phase, wheezing, rales, or rhonchi. Signs of cor pulmonale should be sought: a centrally displaced point of maximal impulse, heart gallop, tricuspid murmur, peripheral edema, jugular venous distention, hepatojugular reflux, and hepatomegaly. This complication of long-standing hypoxemia is associated with substantial mortality.

The causes of exacerbation include respiratory infection, noncompliance with (or under dosing of) medications, changes in weather, exposure to certain drugs (e.g., sedatives or β-blockers), cardiac dysrhythmias, left ventricular dysfunction, and environmental exposure to allergens or other irritants. Most exacerbations are caused by infections, either viral or bacterial, with bacterial infections accounting for 50% of COPD exacerbations. Air pollution and other environmental conditions account for approximately 15% to 20% (9). Table 77.2 lists common respiratory agents associated with COPD exacerbations (10–12). Patients typically present with a gradual, but progressive, deterioration, taking hours to days.

Acute decompensation may be the result of a number of other conditions. Spontaneous pneumothorax in COPD carries a significantly higher complication and mortality rate than in patients with a normal cardiorespiratory status. The patient with chronic bronchitis is predisposed to embolic and thrombotic phenomena because of the hyperviscosity associated with polycythemia. Other disorders, such as congestive heart failure (CHF), pneumonia, acidosis, or renal or hepatic failure, may also overwhelm the COPD patient’s limited reserves, resulting in respiratory failure.

DIFFERENTIAL DIAGNOSIS

Other conditions must also be considered in the patient who presents to the emergency department (ED) with wheezing, cough, dyspnea, or respiratory failure. Pneumonia or acute bronchitis may present with varying degrees of shortness of breath, cough, and bronchospasm, and previously undiagnosed COPD may be discovered after an acute pneumonic process has resolved. The onset of respiratory symptoms in the presence or absence of chest pain, when associated with risk factors such as recent surgery, malignancy, immobility, or extended travel, or leg findings consistent with deep venous thrombosis, strongly suggest pulmonary embolism.

Acute left ventricular dysfunction may mimic many findings of COPD including cough, dyspnea, and hypoxemia, and patients may exhibit wheezing, referred to as “cardiac asthma.” Orthopnea, paroxysmal nocturnal dyspnea, and cardiomegaly favor CHF, but COPD patients with cor pulmonale may demonstrate jugular venous distention and peripheral edema. Classically, chest radiography helped distinguish between these entities, with a lack of cardiomegaly and pulmonary venous redistribution and the presence of bullae and hyperinflation of the lungs suggesting COPD. However, patients with both CHF and COPD who present with dyspnea can present a diagnostic challenge. The rapid laboratory quantification of B-type natriuretic peptide (BNP) may allow more accurate distinction between an acute exacerbation of COPD versus CHF. BNP is secreted from ventricles in response to pressure and volume expansion. Low levels of BNP are consistent with exacerbations of COPD, asthma, bronchitis, or pneumonia, whereas a BNP level of 100 pg/mL or greater is a strong predictor of CHF. Pulmonary embolism or COPD triggering cor pulmonale may also produce elevated BNP levels of 200 to 600 pg/mL (3). Therefore, it is best to use the patient’s physical examination, history, and ancillary studies, together with the BNP level to make the most informed clinical diagnosis and therapeutic decisions.

ED EVALUATION

If the patient’s respiratory status allows a brief history to be taken, attention should be directed to the rapidity of onset, duration of symptoms, precipitating factors, the dosage of medications, and when medications were last taken. Information should be sought regarding the character of the sputum, the course of previous exacerbations, and any history of concomitant disease processes.

The physical examination focuses on the patient’s mental status and the degree of respiratory distress. Hypercapnia and hypoxia can cause confusion, somnolence, and irritability. The cardiac and pulmonary examinations are vital, and repeated examinations are mandatory after therapeutic interventions to monitor the response to treatment.

Pulse oximetry is useful in monitoring oxygen saturation and the effectiveness of oxygen supplementation. Arterial blood gas (ABG) analysis provides information on the PaCO₂ and pH, reflecting adequacy of ventilation. The pH is the best single laboratory marker for gauging the severity of acute respiratory insufficiency, because it reflects the speed and degree of change in PaCO₂ (8). Baseline or prior ABG results may be useful for comparison; in general, hypercapnia with acidemia suggests acute respiratory failure.

The chest radiograph (CXR) is usually done at the bedside, unless the patient is stable and can tolerate being transported to the radiology suite for posteroanterior (PA) and lateral films. The CXR is useful when findings of COPD are present, but it is even more helpful in evaluating for other disease processes, such as pneumothorax, atelectasis, infiltrate, lung mass, or CHF.

Measurements of airflow do not always yield accurate assessments of the severity of illness but may be useful in judging the response to therapy. The peak expiratory flow rate (PEFR) is most commonly used in the ED setting, but, in contrast to the asthmatic patient’s response, it does not correlate well with COPD severity during exacerbations, and does not improve as rapidly as the asthmatic patient’s in response to therapy.

Laboratory studies are generally of limited value. β-Agonists may cause hypokalemia, although this is rarely clinically significant. A complete blood count may reveal anemia, which can compound the problem of hypoxemia, or a high white blood cell count, which may be a clue to pneumonia or other systemic infections. If there is suspicion for CHF or cardiac injury, BNP and troponin assays may be ordered. D-Dimer may be useful for evaluating low-risk patients when pulmonary embolism is being considered.

A 12-lead electrocardiogram (ECG) may suggest right atrial enlargement, low voltage, right ventricular hypertrophy, or strain (cor pulmonale). Acute ischemic patterns must be appreciated to identify an acute coronary event that may be triggering or complicating the acute COPD attack. Continuous ECG monitoring may be useful in revealing dysrhythmias that may aggravate an acute exacerbation.

Thoracic ultrasound is sensitive for ruling out pneumothorax when used by experienced operators. However, it should not be used to diagnose pneumothorax in patients with COPD because there is a high false-positive rate in this population (13).

Thoracic ultrasound is sensitive for ruling out pneumothorax when used by experienced operators. However, it should not be used to diagnose pneumothorax in patients with COPD because there is a high false-positive rate in this population (13).