Definition
A.A chronic airway inflammatory disease defined by a variation of expiratory airflow limitation and history of respiratory symptoms that vary in intensity over time. There are various asthma phenotypes, such as allergic asthma and late-onset asthma.
Incidence
A.Approximately 39.5 million people in the United States have been diagnosed with asthma in their lifetime.
B.It is estimated that 18.9 million adults still have asthma.
C.Asthma accounts for greater than 400,000 hospitalizations, 1.8 million ED visits, and 14.2 million office visits.
D.The prevalence in adults is highest in women and African Americans.
Pathogenesis
A.Interplay among host factors and environmental exposures, resulting in airway inflammation, airflow obstruction, and bronchial hyperresponsiveness.
1.Immune response to antigen, causing activation of T-lymphocytes.
2.Release of cytokines and interleukins, leading to a release of mast cells, eosinophils, and basophils.
3.Subsequent release of inflammatory mediators (e.g., histamine, prostaglandins) that cause airway inflammation and mucus secretion.
B.Resulting development of airway hyperplasia, airway obstruction, and bronchial hyperresponsiveness.
Predisposing Factors
A.Direct and indirect exposure to tobacco smoke.
B.Allergens (e.g., animals such as cats and dogs, dust mites, pollen).
C.Occupational exposures or irritants (e.g., paint, sprays).
D.Pollution.
E.Respiratory infections.
F.Exercise.
G.Stress.
H.Gastroesophageal reflux disease.
I.Obesity.
J.Sex (more likely in female adults).
K.Viral infections.
Subjective Data
A.Common complaints/symptoms.
1.Respiratory symptoms (e.g., wheezing, dyspnea, chest tightness, and cough).
2.Possible extrapulmonary manifestations (e.g., allergic skin conditions or conjunctival irritation).
B.History of the present illness.
1.Onset of asthma and/or symptoms.
2.Precipitating factors.
3.Asthma severity such as frequency of rescue inhaler use.
4.Comorbid conditions that may predispose the patient to developing asthma.
5.Number of exacerbations in the past year.
6.History of ED visits, hospitalizations, and intubations related to asthma.
C.Family and social history.
1.Family history of asthma.
2.Social history such as smoking and inhaled illicit drug use.
3.Employment/environmental factors (e.g., working outside, mining operations, military service).
Physical Examination
A.The physical examination may vary depending on the severity of the asthma and if the patient is having an exacerbation.
B.Expiratory wheezing on auscultation may be audible (see Figure 2.2).
C.Dyspnea may be evident (see Figure 2.1).
D.Changes in mentation (e.g., confusion, lethargy) may be apparent.
E.Patients with moderate to severe asthma exacerbations may be in a tripod position and have tachypnea, absent breath sounds (silent chest) on auscultation, accessory muscle use (e.g., intercostal), and tachycardia.
F.As previously stated, some patients may have extrapulmonary symptoms such as dermatitis, conjunctival irritation, and a swollen nasal mucosa.
Diagnostic Tests
A.Lung function. Initial diagnosis is based on a history of variable symptoms and confirmed variation in expiratory airflow limitation. Lung function is typically normal between symptoms.
1.Evidence of obstruction with reduction in the forced expiratory volume in 1 second/forced vital capacity (FEV1/FVC) and at least one low FEV1.
2.One or more tests documented with excessive variability in lung function.
a.Positive bronchodilator reversibility test with a greater than 12% and 200 mL increase from baseline in the FEV1.
b.Excessive variability of greater than 10% in twice-daily peak expiratory flow (PEF) over 2 weeks.
c.Positive exercise challenge test with decrease in FEV1 of greater than 10% and 200 mL from baseline.
d.Positive bronchial challenge test.
e.Increase in the FEV1 by greater than 12% and 200 mL OR a greater than 20% increase in the PEF from baseline after 4 weeks of treatment.
f.Variation of lung function between office visits.
B.PEF.
1.Can be routinely monitored in the outpatient setting.
2.Repeat values compared with personal best or predicted value by patients.
3.Typically, severe symptoms: At or less than 50% predicted.
FIGURE 2.2 Algorithm for the evaluation of wheezing. ABG, arterial blood gas; COPD, chronic obstructive pulmonary disease.
GERD, gastroesophageal reflux disease; JVD, jugular venous distention; RSV, respiratory syncytial virus
C.Allergy skin testing.
1.Positive allergen test: Allergen not necessarily causing asthma symptoms.
2.Essential to account for the timing of symptoms in relation to allergen exposure and the patient’s history.
D.Chest x-ray.
1.Usually normal in patients with asthma but may reveal hyperinflation.
2.If a patient has a fever in conjunction with respiratory symptoms: May be diagnostic for pneumonia.
E.Pulse oximetry and arterial blood gas (ABG).
1.Used to evaluate for hypoxemia.
2.ABG: Can also be used to evaluate for hypercapnia and respiratory acidosis, especially in those patients presenting with an acute exacerbation.