CHAPTER 7
Pulmonary Diseases
Recent Developments
Sildenafil and tadalafil have been shown to be effective in patients with pulmonary arterial hypertension.
Omalizumab can be used in adults and children 12 years of age and older for the treatment of severe asthma.
Persons with chronic obstructive pulmonary disease who use inhaled corticosteroids are at increased risk for pneumonia.
Obstructive sleep apnea syndrome can be associated with various ocular conditions. Treatment with continuous positive airway pressure can cause dry eye symptoms.
Introduction
The lungs can be affected by numerous pathologic processes, including inflammation (allergic, infectious, autoimmune, toxic), vascular insults, fibrosis, carcinoma, and changes secondary to cardiac or musculoskeletal problems. The functional consequences of the pathology can be divided into obstructive and restrictive ventilatory functions.
Symptoms of lung disease include dyspnea, cough, and wheezing. Dyspnea develops when the demand for gas exchange exceeds the capacity of the respiratory system, as in hypoxemia or hypercapnia. Dyspnea may also reflect the increased work of breathing, as occurs with airway obstruction or reduced compliance of the lungs or chest. Cough develops when mucus, inflammatory debris, or irritants stimulate the bronchi, causing reflex clearing expectoration, or when the lung parenchyma is infiltrated with fluid, cells, or fibrosis. Wheezing occurs when bronchospasm narrows the large airways and exhaled air is forced through narrowed passages.
Obstructive Lung Diseases
In obstructive lung disease, changes in the bronchi, bronchioles, and lung parenchyma can cause airway obstruction. Obstructive diseases can be categorized as reversible or irreversible, although many obstructive lung diseases may have some degree of both reversible and irreversible obstruction.
Reversible obstructive diseases are grouped under the term asthma. In asthma, the airways are hyperresponsive and develop an inflammatory response with bronchospasm to various stimuli, although the specific cause and duration of the bronchospasm vary. In some persons, allergic IgEmediated reactions to defined antigens cause bronchospasm. In many patients, however, the cause of abnormal airway reactivity is unknown. Precipitating factors may include exercise, aspirin, sulfites, tartrazine dye, emotional stress, cold air, environmental pollutants, or viral infection. Bronchial smooth muscle constriction, mucosal edema, excess mucus accumulation, and epithelial cell shedding
all contribute to airway obstruction. This obstruction may be reversible spontaneously or with treatment.
Irreversible obstructive disease (sometimes known as chronic obstructive pulmonary disease [COPD]) comprises a group of conditions in which forced expiratory flow is reduced in either a constant or a slowly progressive manner over months or years. COPD is the fourth leading cause of death in the United States. The Global Initiative for Chronic Obstructive Lung Disease (GOLD), an international consortium working to improve prevention and treatment of COPD, publishes a guide on the diagnosis, classification, and management of this condition. The guide is updated regularly and can be downloaded from the Internet (www.goldcopd.com). GOLD offers a framework for the management of COPD. Some conditions, such as cystic fibrosis or bronchiectasis, either secondary to recurrent necrotizing bacterial infections or occurring as part of Kartagener syndrome, have an identifiable cause. However, most irreversible obstructive diseases, such as emphysema, chronic bronchitis, and peripheral airway disease, cannot be ascribed to specific conditions; rather, they represent an individual response to cigarette smoking and various airborne pollutants. For example, such responses occur in the setting of either α1-antitrypsin deficiency (in certain forms of emphysema) or airway hyperactivity and mucus hypersecretion (as in bronchitis). The pathologic consequences of the abnormal response result in specific damage to lung tissue. Emphysema is characterized by pathologic enlargement of the terminal bronchiole air spaces and by destruction of the alveolar connective tissue septa. Bronchitis is characterized by hypertrophied mucous glands in the bronchi; in peripheral airway disease, only the small airways demonstrate fibrosis, inflammation, and tortuosity.
Global Initiative for Chronic Obstructive Lung Disease. Global strategy for the diagnosis, management, and prevention of chronic obstructive pulmonary disease (updated 2014). www.goldcopd.org. Accessed August 20, 2014.
Restrictive Lung Diseases
The restrictive lung diseases encompass a diverse group of conditions that cause diffuse parenchymal damage. The physiologic consequences of this damage include a reduction in total lung volume, diffusing capacity, and vital capacity. Occasionally, patients without parenchymal involvement who have diseases of the chest wall, respiratory muscles, pleura, or spine may have similarly restricted lung volumes. A fibrotic parenchymal response can result from occupational exposure to various substances, including asbestos, silica dust, graphite, talc, coal, and tungsten. A granulomatous hypersensitivity reaction can develop in response to moldy hay, grains, birds, humidifiers, and cooling systems. Endogenous pulmonary disease can result from collagen vascular diseases, sarcoidosis, eosinophilic granuloma, granulomatosis with polyangiitis (formerly known as Wegener granulomatosis), Goodpasture syndrome, alveolar proteinosis, idiopathic pulmonary hemosiderosis, idiopathic pulmonary fibrosis, and other idiopathic parenchymal diseases. Therapeutic agents such as phenytoin, penicillin, gold, methotrexate, and radiation can also cause pulmonary disease.
Evaluation
Although all patients with respiratory problems should be under the care of a capable internist or pulmonologist, ophthalmologists and other physicians should be aware of the key components in the diagnosis and evaluation of patients with pulmonary diseases. The following should be considered:
Symptoms: Dyspnea, orthopnea, chronic cough, and chronic sputum production. History: Occupational exposure to various substances, family history, cigarette use.
Signs: Audible wheezing, cyanosis, finger clubbing, forced expiratory time greater than 4 seconds, increased anteroposterior diameter of the chest.
Laboratory studies: Elevated hematocrit level and hypoxia or hypercapnia on arterial blood gas measurement.
Chest radiography: Parenchymal disease, hyperinflation, diaphragmatic flattening, increased retrosternal lucency, and pleural abnormalities.
Computed tomography of the chest can detect many abnormalities not seen on chest radiographs: small areas of adenopathy, pulmonary embolus, small nodules, infiltrative lung disease, and bronchiectasis.
Bronchoscopy, transbronchial biopsy, and bronchial lavage: Used to obtain culture material, cytology material, and pathologic specimens for analysis.
Pulmonary function tests measure the mechanical and gas exchange functions of the lungs. The forced expiratory volume over 1 second (FEV1) represents the volume exhaled in the first second of exhalation; the forced vital capacity (FVC) represents the total volume that the patient can exhale. Both parameters and their serial rate of decline in a patient are objective measures of lung function as well as predictors of comorbidity and mortality from lung cancer and cardiovascular disease. An FEV1/FVC ratio less than 70% of predicted suggests obstructive disease; total lung capacity less than 70% of predicted suggests restrictive disease.
Treatment
There are 2 major goals in the treatment of pulmonary disease. The first goal is to favorably alter the natural history of the disease. The second is to improve the patient’s symptoms and functional status and minimize associated problems.
Nonpharmacologic Treatment
Smoking cessation is the single most efficacious and cost-effective intervention in reducing the risk of COPD and slowing its progression. Ophthalmologists should not underestimate the power of even a brief discussion about the impact of smoking and the beneficial effects of smoking cessation. Similarly, avoiding precipitants of airway obstruction is important in ameliorating asthmatic conditions. In patients with severe pulmonary hypertension and cor pulmonale, use of supplemental oxygen to maintain an arterial oxygen pressure above 60 mm Hg confers a modest reduction in pulmonary hypertension and improved survival. However, a patient receiving supplemental oxygen must be carefully monitored because such treatment may decrease the respiratory drive to eliminate carbon dioxide, aggravating the respiratory acidosis that may lead to carbon dioxide narcosis.
Breathing exercises and postoperative chest physiotherapy have demonstrable short-term effects in improving respiratory function.
Noninvasive pressure support ventilation can be used to deliver increased airway pressure. Continuous positive airway pressure (CPAP) throughout the ventilation cycle improves alveolar oxygen exchange. In CPAP therapy, a tight, well-fitting mask is placed over the patient’s mouth and nose or just over the nose. Noninvasive pressure support ventilation is best applied to patients with
respiratory failure who are expected to quickly respond to medical therapy. Intubation and standard ventilation are preferred for patients who require total ventilatory support because the mask may slip and effective ventilation may cease. Nasal CPAP can be used in the management of obstructive sleep apnea syndrome (OSAS). See Chapter 3 for further discussion of this syndrome.
Ophthalmic considerations Floppy eyelid syndrome, keratoconus, and nonarteritic anterior ischemic optic neuropathy (NAION) can be associated with OSAS. Ophthalmologists should be aware that nasal CPAP, which is used in the nonpharmacologic treatment of OSAS and lung diseases, has been reported to modestly increase intraocular pressure in patients with glaucoma and that patients using this therapy can experience symptoms of dry eye.
Archer EL, Pepin S. Obstructive sleep apnea and nonarteritic anterior ischemic optic neuropathy: evidence for an association. J Clin Sleep Med. 2013;9(6):613–618.
Hayirci E, Yagci A, Palamar M, Basoglu OK, Veral A. The effect of continuous positive airway pressure treatment for obstructive sleep apnea syndrome on the ocular surface. Cornea. 2012;31(6):604–608.
Pharmacologic Treatment
Pharmacologic approaches include medications that are specific for the particular pulmonary condition and medications that improve the patient’s symptoms and functional status. Specific medications directly alter the pathophysiologic mechanisms underlying pulmonary disease. Some examples include cyclophosphamide for granulomatosis with polyangiitis, corticosteroids for sarcoidosis, and plasmapheresis with immunosuppressive drugs in Goodpasture syndrome. There is some evidence suggesting that the use of statin medications is associated with a decreased risk of COPD exacerbation.
Symptomatic medications are designed to reduce the obstructive or restrictive components affecting the patient’s lung function. Medications used to treat symptomatic bronchospastic airway obstruction include bronchodilators and inhibitors of inflammation (Table 7-1), as well as antibiotics during infection-precipitated airway closure.
Table 7-1
Bronchodilators, which include theophylline, β-adrenergic agonists, and anticholinergics, act primarily by relaxing the tracheobronchial smooth muscle. β-Adrenergic agonists activate bronchial smooth muscle, resulting in bronchodilation. The selective β2-adrenergics, which have greater bronchodilatory effect and less cardiostimulatory effect, are commonly used, often in metered-dose inhalers (they can also be administered orally or parenterally). These drugs have replaced the nonselective β-adrenergic agents such as isoproterenol. The short-acting β2-agonists include fenoterol, salbutamol, and isoetharine. These drugs differ in onset and duration of action. For example, the onset of action of isoetharine is within 1–3 minutes, and its duration is 60–90 minutes. Common long-acting β2-agonists include formoterol and salmeterol. Salmeterol, a particularly longacting β2-adrenergic, is helpful in maintenance treatment of asthma; it should not be used for acute exacerbations. Although epinephrine causes predominantly β-adrenergic stimulation in the lungs, it also causes peripheral α-adrenergic stimulation, resulting in vasoconstrictive hypertension and tachycardia. Epinephrine is most often administered subcutaneously to help control an acute asthma attack.
Anticholinergic agents directly relax smooth muscle by competing for acetylcholine at muscarinic receptors. Atropine and similar agents have been replaced by poorly absorbing atropinic congeners such as ipratropium bromide, oxitropium bromide, and tiotropium. These inhalation agents have few systemic and minimal cardiac effects. They have an additive bronchodilator effect when combined with submaximal doses of β-adrenergic agonists.
Inhibitors of inflammation include corticosteroids, leukotriene inhibitors, mast-cell stabilizers (cromolyn sodium), and immunosuppressive agents. Corticosteroids not only suppress inflammation of the bronchioles but also potentiate the bronchodilator response to β-adrenergic receptors. Inhaled corticosteroids can be used for an extended period to reduce bronchial hyperreactivity; they are not used to manage acute attacks. Systemic corticosteroids are highly effective in managing acute episodes, but because of the potential adverse effects associated with their use, they should be used only when necessary for serious flare-ups. Leukotriene inhibitors suppress the effects of inflammatory mediators. They are especially useful for prophylaxis and long-term maintenance
therapy in asthma. Cromolyn sodium prevents the release of chemical mediators from mast cells in the presence of IgE antibody and the specific antigen. Immunotherapy has been shown to be helpful for asthma triggered by a defined antigen.
Asthma treatment should be tailored to disease severity. Medication doses should be adequate to control symptoms rapidly and should later be reduced to the minimal level required to maintain control. The goals of therapy should include prevention of symptoms, reduction in frequency and severity of exacerbations, maintenance of normal (or near-normal) pulmonary function, maintenance of normal activity levels, and minimization of medication side effects. Maintenance medications include inhaled corticosteroids, chromones, leukotriene inhibitors, long-acting β2-agonists, anticholinergic agents, and oral corticosteroids. Appropriately used supplemental oxygen increases survival among patients with chronic respiratory failure and has a beneficial effect on pulmonary arterial pressure, polycythemia, exercise capacity, lung mechanics, and mental state.
Baena-Cagnani CE, Gómez RM. Current status of therapy with omalizumab in children. Curr Opin Allergy Clin Immunol. 2014;14(2):149–154.
Wang MT, Lo YW, Tsai CL, et al. Statin use and risk of COPD exacerbation requiring hospitalization. Am J Med. 2013;126(7):598–606.
Perioperative Considerations
Before operating on a patient with lung disease, the surgeon should consult with an internist or pulmonologist to carefully define the patient’s functional respiratory status, especially with respect to the supine position. The patient’s respiratory function should be maximized with medications and nonpharmacologic means, as appropriate. He or she should be sedated only if necessary and, in that case, should be carefully monitored for arterial gas values. Also see the section Respiratory Diseases in Chapter 15.