Chronic Obstructive Pulmonary Disease

Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a disease  state characterized by airflow limitation that is not fully reversible.This newest definition of COPD, provided by the Global Initiative for Chronic Obstructive Lung Disease, provides a broad description that better explains this disorder and its signs and symptoms (National Institutes of Health [NIH], 2001). While previous definitions have included emphysema and chronic bronchitis under the umbrella classification of COPD, this was often confusing because most patients with COPD present with overlapping  signs  and  symptoms  of  these  two  distinct  disease processes.

COPD may include diseases that cause airflow obstruction(eg, emphysema, chronic bronchitis) or a combination of these disorders. Other diseases such as cystic fibrosis, bronchiectasis, and asthma were previously classified as types of chronic obstructive lung disease. However, asthma is now considered a separate disorder and is classified as an abnormal airway condition characterized primarily by reversible inflammation. COPD can coexist with asthma. Both of these diseases have the same major symptoms; however, symptoms are generally more variable in asthma than in COPD.

COPD is the fifth leading cause of death in the United States for all ages and both genders; fifth for men and fourth for women(National Center for Health Statistics [NCHS], 2000). In 1998,more than 12,000 persons died of COPD. This represents a rise in the mortality rate for this disorder at a time when death ratesfrom other serious illnesses, such as heart disease and cerebral vascular disease, were declining. Approximately 16 million people in the United States have some form of COPD; it is responsible for over 13.4 million office visits per year and is the third most frequent justification for home care services (NCHS, 2000; National Heart, Lung and Blood Institute [NHLBI], 1998). People with COPD commonly become symptomatic during the middle adult years, and the incidence of COPD increases with age. Although certain aspects of lung function normally decrease with age (eg, vital capacity and forced expiratory volume in 1 second [FEV1]), COPD accentuates and accelerates these physiologic changes.

Pathophysiology

In COPD, the airflow limitation is both progressive and associated with an abnormal inflammatory response of the lungs to noxious particles or gases. The inflammatory response occurs throughout the airways, parenchyma, and pulmonary vasculature (NIH,2001). Because of the chronic inflammation and the body’s attempts to repair it, narrowing occurs in the small peripheral airways. Over time, this injury-and-repair process causes scar tissue formation and narrowing of the airway lumen. Airflow obstruction may also be due to parenchymal destruction as seen with emphysema, a disease of the alveoli or gas exchange units.In addition to inflammation, processes relating to imbalances of proteinases and antiproteinases in the lung may be responsible for airflow limitation. When activated by chronic inflammation, proteinases and other substances may be released, damaging the parenchyma of the lung. The parenchymal changes may also be consequences of inflammation, environmental, or genetic factors(eg, alpha1 antitrypsin deficiency).Early in the course of COPD, the inflammatory response causes pulmonary vasculature changes that are characterized by thickening of the vessel wall. These changes may occur as a result of exposure to cigarette smoke or use of tobacco products or as a result of the release of inflammatory mediators (NIH, 2001).

Chronic Bronchitis

Chronic bronchitis, a disease of the airways, is defined as the presence of cough and sputum production for at least 3 months in each of 2 consecutive years. In many cases, smoke or other environmental pollutants irritate the airways, resulting in hypersecretionof mucus and inflammation. This constant irritation causes the mucus-secreting glands and goblet cells to increase in number, ciliary function is reduced, and more mucus is produced. The bronchial walls become thickened, the bronchial lumen is nar-rowed, and mucus may plug the airway (Fig. 24-1). Alveoli adja-cent to the bronchioles may become damaged and fibrosed, resulting in altered function of the alveolar macrophages. This is significant because the macrophages play an important role in de-stroying foreign particles, including bacteria. As a result, the pa-tient becomes more susceptible to respiratory infection. A wide range of viral, bacterial, and mycoplasmal infections can produce acute episodes of bronchitis. Exacerbations of chronic bronchitis are most likely to occur during the winter.

Emphysema

In emphysema, impaired gas exchange (oxygen, carbon dioxide) results from destruction of the walls of overdistended alveoli. “Emphysema” is a pathological term that describes an abnormal distention of the air spaces beyond the terminal bronchioles, with destruction of the walls of the alveoli. It is the end stage of a process that has progressed slowly for many years. As the walls of the alveoli are destroyed (a process accelerated by recurrent in-fections), the alveolar surface area in direct contact with the pul-monary capillaries continually decreases, causing an increase in dead space (lung area where no gas exchange can occur) and im-paired oxygen diffusion, which leads to hypoxemia. In the later stages of the disease, carbon dioxide elimination is impaired, resulting in increased carbon dioxide tension in arterial blood (hypercapnia) and causing respiratory acidosis. As the alveolar walls continue to break down, the pulmonary capillary bed is re-duced. Consequently, pulmonary blood flow is increased, forcing the right ventricle to maintain a higher blood pressure in the pul-monary artery. Hypoxemia may futher increase pulmonary artery pressure. Thus, right-sided heart failure (cor pulmonale) is one of the complications of emphysema. Congestion, dependent edema, distended neck veins, or pain in the region of the liver suggests the development of cardiac failure.

There are two main types of emphysema, based on the changes taking place in the lung: panlobular (panacinar) and centrilobular (centroacinar) (Fig. 24-2). Both types may occur in the same patient.

In the panlobular (panacinar) type, there is destruction of the respiratory bronchiole, alveolar duct, and alveoli. All air spaces within the lobule are essentially enlarged, but there is little in-flammatory disease. The patient with this type of emphysema typically has a hyperinflated (hyperexpanded) chest (barrel chest on physical examination), marked dyspnea on exertion, and weight loss. To move air into and out of the lungs, negative pres-sure is required during inspiration, and an adequate level of pos-itive pressure must be attained and maintained during expiration. The resting position is one of inflation. Instead of being an in-voluntary passive act, expiration becomes active and requires muscular effort. The patient becomes increasingly short of breath, the chest becomes rigid, and the ribs are fixed at their joints.

In the centrilobular (centroacinar) form, pathologic changes take place mainly in the center of the secondary lobule, preserv-ing the peripheral portions of the acinus. Frequently, there is a derangement of ventilation–perfusion ratios, producing chronic hypoxemia, hypercapnia (increased CO₂ in the arterial blood), polycythemia, and episodes of right-sided heart failure. Thisleads to central cyanosis, peripheral edema, and respiratory fail-ure. The patient may receive diuretic therapy for edema.

Risk Factors

Risk factors for COPD include environmental exposures and host factors (Chart 24-1). The most important risk factor for COPD is cigarette smoking. Pipe, cigar, and other types of to-bacco smoking are also risk factors. In addition, passive smok-ing contributes to respiratory symptoms and COPD (NIH, 2001). Smoking depresses the activity of scavenger cells and af-fects the respiratory tract’s ciliary cleansing mechanism, which keeps breathing passages free of inhaled irritants, bacteria, and other foreign matter. When smoking damages this cleansing mechanism, airflow is obstructed and air becomes trapped be-hind the obstruction. The alveoli greatly distend, diminishing lung capacity. Smoking also irritates the goblet cells and mucus glands, causing an increased accumulation of mucus, which in turn produces more irritation, infection, and damage to the lung. In addition, carbon monoxide (a byproduct of smoking) com-bines with hemoglobin to form carboxyhemoglobin. Hemoglo-bin that is bound by carboxyhemoglobin cannot carry oxygen efficiently.

Smoking is not the only risk factor for COPD. Other factors include prolonged and intense exposure to occupational dusts and chemicals, indoor air pollution, and outdoor air pollution, which adds to the total burden of inhaled particles on the lung (NIH, 2001).

A host risk factor for COPD is a deficiency of alpha₁ anti-trypsin, an enzyme inhibitor that protects the lung parenchyma from injury. This deficiency predisposes young patients to rapid development of lobular emphysema even in the absence of smok-ing. Alpha₁antitrypsin deficiency is one of the most common genetically linked lethal diseases among Caucasians and affects approximately one in every 3,000 Americans or approximately 80,000 to 100,000 cases (George, San Pedro & Stoller, 2000). The genetically susceptible person is sensitive to environmental factors (smoking, air pollution, infectious agents, allergens) and in time develops chronic obstructive symptoms. Carriers of this genetic defect must be identified so that they can modify envi-ronmental risk factors to delay or prevent overt symptoms of disease. Genetic counseling should also be offered. Alpha-protease inhibitor replacement therapy, which slows the progression of the disease, is available for patients with this genetic defect and for those with severe disease. This intermittent infusion therapy is costly and is required on an ongoing basis.

Clinical Manifestations

COPD is characterized by three primary symptoms: cough, spu-tum production, and dyspnea on exertion (NIH, 2001). These symptoms often worsen over time. Chronic cough and sputum production often precede the development of airflow limitation by many years. However, not all individuals with cough and spu-tum production will develop COPD. Dyspnea may be severe and often interferes with the patient’s activities. Weight loss is com-mon because dyspnea interferes with eating, and the work of breathing is energy-depleting. Often the patient cannot partici-pate in even mild exercise because of dyspnea; as COPD pro-gresses, dyspnea occurs even at rest. As the work of breathing increases over time, the accessory muscles are recruited in an ef-fort to breathe. The patient with COPD is at risk for respiratory insufficiency and respiratory infections, which in turn increase the risk for acute and chronic respiratory failure.

In COPD patients with a primary emphysematous compo-nent, chronic hyperinflation leads to the “barrel chest” thorax con-figuration. This results from fixation of the ribs in the inspiratory position (due to hyperinflation) and from loss of lung elasticity (Fig. 24-3). Retraction of the supraclavicular fossae occurs on in-spiration, causing the shoulders to heave upward (Fig. 24-4). In advanced emphysema, the abdominal muscles also contract on inspiration.

Assessment and Diagnostic Findings

The nurse should obtain a thorough health history for a patient with known or potential COPD. Chart 24-2 lists the key factors to assess. Pulmonary function studies are used to help confirm the diagnosis of COPD, determine disease severity, and follow dis-ease progression. Spirometry is used to evaluate airflow obstruc-tion, which is determined by the ratio of FEV₁ (volume of air that the patient can forcibly exhale in 1 second) to forced vital capac-ity (FVC). Spirometric results are expressed as an absolute vol-ume and as percent-predicted using appropriate normal values for gender, age, and height. With obstruction, the patient either has difficulty exhaling or cannot forcibly exhale air from the lungs, reducing the FEV₁. Obstructive lung disease is defined as a FEV₁/FVC ratio of less than 70%.

In addition, bronchodilator reversibility testing may be per-formed to rule out the diagnosis of asthma and to guide initial treatment. With this type of testing, spirometry is first obtained, then the patient is given an inhaled bronchodilator per a proto-col, and finally spirometry is repeated. The patient demonstrates a degree of reversibility if the pulmonary function values improve after administration of the bronchodilator.

Arterial blood gas measurements may also be obtained to as-sess baseline oxygenation and gas exchange. In addition, a chest x-ray may be obtained to exclude alternative diagnoses. Lastly, alpha₁ antitrypsin deficiency screening may be performed for pa-tients under age 45 or for those with a strong family history of COPD.

The severity of COPD is classified into four stages (Table 24-1) (National Institutes of Health, 2001). Factors that determine the clinical course and survival of patients with COPD include history of cigarette smoking, passive smoking exposure, age, rate of decline of FEV₁, hypoxemia, pulmonary artery pressure, resting heart rate, weight loss, and reversibility of airflow obstruction (George, San Pedro & Stoller, 2000).

In diagnosing COPD, several differential diagnoses must be ruled out. The primary differential diagnosis is asthma. Key characteristics of asthma include onset often early in life, variation in daily symptoms and day-to-day occurrence or timing of symp-toms, family history of asthma, and a largely reversible airflow ob-struction. It may be difficult to differentiate between a patient with COPD and one with chronic asthma. A key part of differ-entiation is the patient history, as well as the patient’s respon siveness to bronchodilators. Other diseases that must be considered in the differential diagnosis include heart failure, bronchiectasis, and tuberculosis (NIH, 2001).

Complications

Respiratory insufficiency and failure are major life-threatening complications of COPD. The acuity of the onset and the sever-ity of respiratory failure depend on the patient’s baseline pul-monary function, pulse oximetry or arterial blood gas values, comorbid conditions, and the severity of other complications of COPD. Respiratory insufficiency and failure may be chronic (with severe COPD) or acute (with severe bronchospasm or pneumonia in the patient with severe COPD). Acute respiratory insufficiency and failure may necessitate ventilatory support until other acute complications, such as infection, can be treated.