Complications of Chronic Obstructive Pulmonary Disease
Lower extremity edema (swelling) in a patient with COPD is usually a sign of cor pulmonale (pulmonary hypertension and right-sided heart failure). COPD makes the heart work harder, especially the right side, which pumps blood into the lungs. Because of poor gas exchange in COPD, there are decreased amounts of oxygen in the blood causing blood vessels to constrict. Many of the capillaries surrounding the alveoli are destroyed in the disease process making the heart work harder to force blood through fewer constricted blood vessels. As a result of this effort, the right ventricle becomes enlarged, the walls of the heart thicken, and the chamber eventually loses its ability to contract efficiently.
Acute exacerbations of COPD are characterized by an abrupt increase of symptoms. Cough and sputum production increases. Wheezing is often increased or noted for the first time. Dyspnea (shortness of breath) is increased or apparent for the first time. Exacerbations are caused by bronchial infections in most instances. Fever is uncommon. A person with COPD may initially have one or two acute exacerbations per year, which resolve readily with therapy. The number of exacerbations per year increases as the diseases progresses.
During an acute exacerbation, there is increased airway narrowing due to bronchospasm (contraction of the bronchi and bronchioles), edema, and excessive mucus production. If narrowed airways cause an extreme increase in the work of breathing that cannot be maintained, the patient will die, unless there is intervention (see Mechanical Ventilation). Often the patient needs mechanical support until the acute decline has resolved. Unfortunately, some patients don't recover sufficiently from the acute episode to enable them to breathe on their own. There is no way of knowing who will improve and who will not after such an episode. Generally, those who have worse lung function and functional status are less likely to regain independent breathing.
End-stage Lung Disease
When respiratory failure occurs in a patient who has end-stage lung disease, there is a slow decline in lung function and rising levels of carbon dioxide in the blood. The increasing carbon dioxide creates a narcotic effect in the patient, who slowly loses consciousness and stops breathing.
Respiratory failure can occur during an acute exacerbation of COPD or in a patient who has end-stage lung disease.
Other COPD Complications
Other complications of COPD include pneumonia, polycythemia, and pneumothorax. Pneumonia caused by bacterial infection can lead to respiratory failure in these patients. Streptococcus pneumoniae is the most common cause of bacterial pneumonia in patients with COPD.
Pneumothorax occurs when a hole develops in the lung, allowing air to escape into the space between the lung and the chest wall and collapsing the lung. Patients with COPD are at increased risk for spontaneously developing these holes because of weakened lung structure. A pneumothorax can lead to severe respiratory distress and is treated by inserting a tube into the space between the lung and the chest wall (pleural space) to allow the air to escape out of the space and re-expanding the lung. The tube must remain in the space until the hole is repaired.
Polycythemia in COPD is the body's attempt to adjust to decreased amounts of blood oxygen by increasing the production of oxygen-carrying red blood cells. While this may be helpful in the short term, overproduction eventually clogs small blood vessels.
The overall prognosis for a patient with COPD depends on the severity of lung disease and whether the patient continues to smoke. An FEV1 (forced expiratory volume after 1 second) greater than 50% predicted carries a very good prognosis, with the survival of these patients being only slightly less than patients without COPD. Patients with an FEV1 less than 0.75 L (very severe obstruction, less than 30% predicted), have a 1-year mortality rate of 30% and a 10-year mortality rate of 95%. At any level of lung impairment, prognosis improves when the patient quits smoking.