38: Reactive Airway Disease

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CHAPTER 38 Reactive Airway Disease

Malcolm Packer, MD

1 Define reactive airway disease, in particular, asthma

The term reactive airway disease (RAD) is used to describe a family of diseases that shares an airway sensitivity to physical, chemical, or pharmacologic stimuli. This sensitivity results in a bronchoconstrictor response and is seen in patients with asthma, chronic obstructive pulmonary disease (COPD), emphysema, viral upper respiratory illness, and other disorders.

Asthma is defined by the American Thoracic Society as “a disease characterized by an increased responsiveness of the trachea and bronchi to various stimuli manifested by a widespread narrowing of the airways that changes in severity either spontaneously or as a result of therapy.” Asthma is manifested by episodes of dyspnea, cough, and wheezing. These symptoms are related to the increased resistance to airflow in the patient’s airways.

2 What are the different types of asthma?

Although the common denominator lies in airway hyperreactivity, patients may fit into two subgroups: allergic (extrinsic) and idiosyncratic (intrinsic). Many believe that the terms extrinsic and intrinsic should be discarded. Underlying all types of asthma are airway hyperreactivity, inflammation, and an interaction between allergic and nonallergic stimuli.

Allergic asthma is thought to result from an immunoglobulin E–mediated response to antigens such as dust and pollen. Among the mediators released are histamine, leukotrienes, prostaglandins, bradykinin, thromboxane, and eosinophilic chemotactic factor. Their release leads to inflammation, capillary leakage in the airways, increased mucus secretion, and bronchial smooth muscle contraction.

Idiosyncratic asthma is mediated by nonantigenic stimuli, including exercise, cold, pollution, and infection. Bronchospasm is caused by increased parasympathetic (vagal) tone. Although the primary stimulus differs, the same mediators as allergic asthma are released (and some patients with allergic asthma have enhanced vagal tone).

3 What diseases mimic asthma?

Upper and lower airway obstruction from tumor, aspirated foreign bodies, or stenosis

Left ventricular failure (cardiac asthma) and pulmonary embolism

Gastroesophageal reflux and aspiration

Viral respiratory illnesses (e.g., respiratory syncytial virus)

Allergic reactions and anaphylaxis

A careful history and physical examination will differentiate these diseases from primary reactive disease

4 What are the important historical features of an asthmatic patient?

Duration of disease

Frequency, initiating factors, and duration of attacks

Has the patient ever required inpatient therapy? Did the patient require intensive care admission or intubation?

What are the patient’s medications, including daily and as-needed usage, over-the-counter medications, and steroids?

5 What physical findings are associated with asthma?

The most common physical finding is expiratory wheezing. Wheezing is a sign of obstructed airflow and is often associated with a prolonged expiratory phase. As asthma progressively worsens, patients use accessory respiratory muscles. A significantly symptomatic patient with quiet auscultatory findings may signal impending respiratory failure because not enough air is moving to elicit a wheeze. Patients also may be tachypneic and probably are dehydrated; they prefer an upright posture and demonstrate pursed-lip breathing. Cyanosis is a late and ominous sign.

6 What preoperative tests should be ordered?

The patient’s history guides the judicious ordering of preoperative tests. A mild asthmatic maintained on as-needed medication who is currently healthy will not benefit from preoperative testing. Symptomatic patients with no recent evaluation deserve closer attention.

The most common test is a pulmonary function test, which allows simple and quick evaluation of the degree of obstruction and its reversibility (see Chapter 9). A comparison of values obtained from the patient with predicted values helps to assess the degree of obstruction. Severe exacerbation correlates with a peak expiratory flow rate (PEFR) or forced expiratory volume in 1 second (FEV₁) of less than 30% to 50% of predicted, which for most adults is a PEFR of less than 120 L/min and an FEV₁ of less than 1 L. Tests should be repeated after a trial of bronchodilator therapy to assess reversibility and response to treatment.

Arterial blood gases are usually not helpful. Electrocardiograms, chest radiographs, and blood counts are rarely indicated for evaluation of asthma unless particular features of the patient’s presentation suggest alternative diagnoses (e.g., fever and rales suggesting pneumonia).