Asthma - Pulmonary - Medbullets Step 2/3

Snapshot

A 5-year-old is brought to his pediatrician’s office by his parents because he cannot keep up with his friends while playing outside because he is short of breath. His parents report that they notice him occasionally coughing at night but he is otherwise healthy. On physical exam, respiratory rate is within normal limits and slight end expiratory wheezing is appreciated diffusely.

Introduction

Clinical definition
- a reversible, intermittent obstructive disease of the small airways characterized by inflammation and hyperresponsiveness
Epidemiology
- can present at any age
- most common chronic pediatric disease
- risk factors
  - atopy
    - strongest identifiable factor
    - atopic dermatitis
    - food allergies
    - allergic rhinitis
  - family history
  - smoking
  - obesity
  - air pollution
Pathogenesis
- acute, subacute, or chronic inflammation
- an elevated level of IgE binds mast cells and triggered by an antigen to release histamine and initiate an inflammatory cascade
  - common triggers
    - allergies (house dust mites)
    - upper respiratory infection
    - cold air
    - exercise
- obstruction secondary to airway hyperresponsiveness, edema, mucus plugging, and smooth muscle hypertrophy
Classification based on daytime and nighttime symptoms

Asthma Classification
Severity	Symptom Frequency	Pulmonary Function Test
Intermittent	≤2 days/week ≤2 nights/month	FEV1 > 80% of predicted
Mild persistent	> 2/week but < 1/day > 2 nights/month	FEV1 ≥ 80% of predicted
Moderate persistent	Daily daytime > 1 night/week	FEV1 60-80% of predicted
Severe persistent	Continual daytime Frequent nighttime	FEV1 < 60% of predicted

Presentation

Symptoms
- often worse in the early morning and at night
- wheezing
- productive cough
- shortness of breath
- chest tightness
Physical exam
- chronic asthma
  - possibly normal
  - wheezing
- acute exacerbation
  - wheezing
  - accessory muscle usage
  - paradoxical breathing
  - decreased breath sounds
  - prolonged expiratory phase
  - tachypnea
  - pulsus paradoxus
  - hyperresonance
Special presentations
- Samter triad
  - aspirin and nonsteroidal anti-inflammatory drug sensitivity, asthma, and nasal polyps
- exercise induced bronchoconstriction
  - only associated with exercise
- cough variant
  - only cough symptoms

Studies
Diagnostic testing diagnostic approach in acute exacerbation of asthma provide supportive care and lifesaving treatments first use peak expiratory flow rate to monitor pulmonary function test as an outpatient later imaging chest radiograph may be normal hyperinflammation if severe studies pulmonary function tests gold standard peak expiratory flow rate can be used at home to monitor obstruction < 50% of personal best indicates a severe obstruction arterial blood gas mild hypoxia with early respiratory alkalosis due to tachypnea normalization of PCO₂ could indicate fatigue and impending respiratory failure interpret in the context of the overall clinical picture if severe, respiratory acidosis due to CO₂ retention Diagnostic criteria pulmonary function tests an obstructive pattern of FEV1/FVC < 70% is consistent with diagnosis if consistent with obstructive lung disease, reverse with a beta-agonist increase of ≥ 12% from baseline and ≥ 200 mL if normal in a well patient but high clinical suspicion, induce with a methacholine challenge decrease of ≥ 20% from baseline increased residual volume and TLC normal DLCO
Differential
Anaphylaxis distinguishing factors swollen mouth, hypotension, and gastrointestinal symptoms Foreign object lodged in the respiratory tract distinguishing factors foreign object visualized on chest radiograph Post nasal drip distinguishing factors frequent throat clearing, nonproductive cough, normal FEV1 and cardiopulmonary exam treatment: first-generation antihistamines (e.g. diphenhydramine) Congestive heart failure distinguishing factors volume overload visualized on chest radiograph and physical exam Gastroesophageal reflux disease distinguishing factors sour taste, regurgitation, and burning sensation

Treatment of Acute Exacerbations
Management approach administer lifesaving treatments and monitor serially with for signs of respiratory failure physical examinations peak expiratory flow rate ABG Medical first-line humidified O₂ β2-agonists via metered dose inhaler or nebulizer magnesium relaxes smooth muscle reduces hospital admissions second-line intravenous methylprednisone indication if poor response to first-line treatment aminophylline Interventional non-invasive positive pressure indication if poor response to medical management above only appropriate for alert patients with intact airway intubation indications if continued threat of airway obstruction despite first-line and second-line treatment if unable to protect airway due to reduced consciousness if PCO₂ normalizes or is elevated (patient should be hyperventilating leading to low PCO₂, if the patient becomes fatigued, PCO₂ will begin to increase)
Treatment of Chronic Asthma
Management approach based on a step-wise approach building upon existing therapy all patients should have a short-acting β2-agonists as needed Therapy based on the classification intermittent treat with short-acting β2-agonists as needed no daily long-term treatment needed mild persistent add low-dose inhaled corticosteroid predisposes to oral candidiasis ("thrush") moderate persistent add long-acting β2-agonist to inhaled low-dose corticosteroid alternative: add leukotriene modifier or theophylline alternative: inhaled medium-dose corticosteroid only severe persistent inhaled medium- or high-dose corticosteroid with long-acting inhaled β2-agonist if continued poor control, consider oral corticosteroids or omalizumab (anti-IgE) Other medical management strategies cromolyn indication exercise prophylaxis montelukast indication exercise prophylaxis or aspirin-induced asthma inhaled β2-agonists indication prior to exposure to triggers such as exercise Lifestyle modifications including allergy avoidance
Complications
Acute respiratory failure Status asthmaticus Atelectasis Pneumothorax Use of non-specific β-blockers (i.e., blocking β2) can close airways leading to death