Asthma is a chronic respiratory disease associated with reversible airflow obstruction, bronchial hyperresponsiveness (BHR), and airway inflammation triggered by various s

Amelia Mangune

Posted Date

Jun 23, 2022, 12:05 AM

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Asthma 

Asthma is a chronic respiratory disease associated with reversible airflow obstruction, bronchial hyperresponsiveness (BHR), and airway inflammation triggered by various stimuli, including viral upper respiratory infection, environmental allergens, and occupational exposures. It can lead to recurrent episodes of wheezing, cough, and dyspnea (Holguin, 2017). 

Presentation (Holguin, 2017) 

• H&P reveals recurrent respiratory symptoms characterized by wheezing, cough, and chest tightness. 
• Trigger exposures may exacerbate respiratory symptoms and include exposure to airway irritants (smoke, strong fumes, air pollution, etc.), aeroallergens, respiratory infections, and cold air. 
• Psychological stress and physical exercise may also trigger respiratory symptoms without any other concomitant exposures.
• Respiratory symptoms may have a nocturnal predominance and are frequently more severe in the morning after waking up when airflows are usually lower. 
• Other presentation includes tachypnea, tachycardia, non-productive cough, prolonged expiration, use of accessory muscles in severe attack, and decreased exercise tolerance (Bray, 2018).

Categories of Asthma Severity (Fanta & Barrett, 2022)

Intermittent:

• Daytime asthma symptoms happen 2 or fewer days per week.
• Two or fewer nocturnal awakenings per month.
• Use short-acting beta-agonists (SABAs) to relieve symptoms two or fewer days per week.
• No interference with normal activities between exacerbations.
• FEV1 measurements between exacerbations are consistently within the normal range (i.e., ≥80% of predicted).
• FEV1/FVC ratio between exacerbations is normal.
• One or no exacerbations require oral glucocorticoids per year.

Mild persistent:

• Symptoms > 2Xweekly (although < daily).
• About 3-4 nocturnal awakenings per month due to asthma (but fewer than every week).
• Use SABAs to relieve symptoms > 2 days/week (but not daily).
• Minor interference with normal activities
• FEV1 measurements within normal range (≥80% of predicted).

Moderate persistent:

• Everyday manifestations of asthma.
• Nocturnal awakenings as often as once per week.
• Daily requirement for SABAs for symptom relief.
• Some limitations in normal activity.
• FEV1 ≥60 and <80% of predicted and FEV1/FVC below normal.

Severe persistent:

• Presence of asthma symptoms throughout the day. 
• Nocturnal awakening due to asthma every night. 
• Reliever prescription needed for symptoms several times/day. 
• Severe activity limitation due to asthma. 

Pathophysiology

The early phase of asthma (1st hour) is triggered by IgE antibodies that are sensitized and released by plasma cells (Sinyor & Perez, 2022). Based on Sinyor & Perez (2022), these antibodies respond to environmental triggers. IgE antibodies then bind to high-affinity mast cells and basophils. When a pollutant or risk factor gets inhaled, the mast cells release cytokines and eventually de-granulate. Released from mast cells are histamine, prostaglandins, and leukotrienes. These cells, in turn, contract the smooth muscle and cause airway tightening. In the late phase (4-6 hrs), eosinophils, basophils, neutrophils, and helper and memory T-cells all localize to the lungs, which causes bronchoconstriction and inflammation. As a result of inflammation and bronchoconstriction, there is an intermittent airflow obstruction, resulting in increased work of breathing.

Labs/Diagnostics (Holguin, 2017) 

Pulmonary Function Test

• Reveals evidence of airway obstruction with a bronchodilator response > or = 12% (or 200 mL) improvement of FEV1 after short-acting bronchodilators.
• Bronchodilation should only be evaluated after withholding asthma medications for at least 4 hrs for short-acting β2-receptor agonists (SABA) and 24 hrs for long-acting β2-receptor agonists (LABA).

Methacholine (a cholinergic agent utilized to stimulate bronchial constriction excludes asthma). 

• A positive test occurs when a reduction in FEV1 > or = 20% from the baseline postmethacholine level. The methacholine test is very sensitive but lacks specificity so that a positive test can be seen in other airway diseases or allergies. 
• Diligent assessment for the existence or lack of asthma through testing and evaluation of treatment response will help eliminate the roughly 30% of patients who are mistakenly diagnosed with this condition clinically (false positive) and are unnecessarily treated with corticosteroids.

Other studies (Bray, 2018)

• Spirometry
• Allergy testing (consider)
• Peak flow monitoring

Differential Diagnosis (Holguin, 2017): 

Congestive heart failure 

• Wheezing and coughing can happen, which may be linked with airway vascular congestion and peribronchial cuffing due to pulmonary edema, bibasilar inspiratory crackles on auscultation, and an elevated serum BNP. 

Airway obstruction 

• Foreign body aspiration, tumor, laryngeal edema, anaphylaxis, and laryngospasm could lead to stridor, which can be mistaken for wheezing.

Other differential diagnoses (Bray, 2018)

• Respiratory infection
• GERD
• Habitual non-asthma-related cough
• Tuberculosis

Treatment (Holguin, 2017) 

• Supplemental O2
• Inhaled SABA 
• Anticholinergic agents
• Nebulizers
• Oral systemic corticosteroids

Patient Education and Prevention (Bray, 2018):

• Identify and minimize known asthma triggers by avoiding allergens and irritants.
• Take prescribed asthma medications daily.
• Learn how to identify early signs/symptoms of asthma exacerbation (frequency of dyspnea, cough, chest tightness, and the need for quick-relief medication).
• Have an "asthma action plan," a preplanned medication plan for an exacerbation.
• Influenza and Pneumococcal Pneumonia vaccinations.
• Monitor peak flow values.
• Learn the correct use of inhalers, spacers, and other medications (about half of patients misuse inhalers, causing medications ineffective).
• Routine follow-up visit ( 1 to 6 mons depending on the severity of asthma).

Referrals (Fanta & Barrett, 2022)

Pulmonologist 

• If there is uncertainty about asthma diagnosis, poorly-controlled asthma, an episode of near-fatal asthma, treatment of comorbid conditions, or the need for bronchoscopy.

Allergist/Immunologist

•  If considering the need for specialized diagnostic studies (e.g., allergy skin testing) or potential treatment with biologics.

References

Bray, S.L. (2018). Asthma. In Hollier, A. (Ed). Clinical Guidelines In Primary Care (2nd Ed, pp. 662-669). Advanced Practice Education Associates, Inc.

La Fayette, LA.

Fanta, C.H. & Barrett, N.A. (June 06, 2022). An overview of asthma management. UpToDate. https://www.uptodate.com/contents/an-overview-of-asthma-management?source=history_widget#H31

Holguin, F. (2017). Asthma. In McKean, S.C., Ross, J.J. Dressler, D.D. & Scheurer, D.B. (Eds.). Principles and Practice of Hospital Medicine (2nd ed., Chap. 231, pp. 4507-4509). McGraw-Hill Education. 

Sinyor, B. & Perez, L.C. (May 08, 2022) Pathophysiology of asthma. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK551579/