Asthma Lecture Notes

Introduction

• Focus: Asthma (Part of Clinical Medicine section)
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Overview of Asthma

• Asthma: Obstructive lung disease
• Common Chief Complaints: Dyspnea (shortness of breath), wheezing, and sometimes cough
• Physical Exam Findings: Hyperresonance to percussion

Pathophysiology of Asthma

• Bronchial Wall Edema: Inflammation causing narrowed airways
  • Results in difficulty moving CO2 out and O2 in
• Mucus Production: Activated goblet cells secrete mucus, further narrowing airways
• Bronchoconstriction (Bronchospasm): Smooth muscle contraction within the bronchial walls
  • Causes problems with air movement, leading to dyspnea and wheezing
  • Irritation from mucus/inflammation can provoke cough
  • All factors contribute to airway obstruction

Air Trapping and Hyperinflation

• Air Trapping: Difficult to exhale, leading to hyperinflated lungs
• Visualization: Picture holding a deep breath and trying to breathe in more—hyperinflation makes breathing in and out difficult

Triggers and Mechanisms

• Common Triggers: Allergies, certain medications (e.g., aspirin), beta blockers, viral infections, cold air, exercise
• Atopic Triad: Allergies, atopic dermatitis, asthma
• Samter's Triad: Asthma, aspirin sensitivity, nasal polyps
• Cellular Mechanisms: Interaction between allergens, dendritic cells, T-helper cells, cytokines (IL-4, IL-5), eosinophils, plasma cells, mast cells
  • Leads to release of histamines, leukotrienes causing bronchial edema, mucus production, bronchospasm
• Overall Effect: Airway obstruction leading to symptoms

Severe Asthma and Complications

• Status Asthmaticus: Extreme form of asthma leading to respiratory failure
  • Mechanism: Severe bronchial wall edema, mucus, bronchospasm
  • Consequences: High CO2 (hypercapnia), low O2 (hypoxia), air trapping, respiratory failure
• Respiratory Failure Type: Hypercapnic (Type 2), indicated by high CO2 and low O2
• Signs to Watch: Increased respiratory rate, increased work of breathing, use of accessory muscles, wheezing, hyperresonance, prolonged expiration, potential silent chest, pulses paradoxus
• Secondary Pneumothorax: Pneumothorax due to hyperinflated lungs bursting small blebs

Diagnostic Approach

• Initial Workup: Chest X-ray, ECG, ABG (Arterial Blood Gas)
  • Chest X-ray: Often normal, could show hyperinflation during exacerbations
  • ECG: Usually normal
  • ABG: Respiratory alkalosis in mild/moderate cases; respiratory acidosis in severe cases
• PFTs (Pulmonary Function Tests): Relevant in non-exacerbating phases
  • FEV1/FVC Ratio: Indicates obstruction if ratio <70%
  • Methacholine Challenge: Induces bronchoconstriction, FEV1 drops >20%
  • Bronchodilator Test: Albuterol improves FEV1 by >12%, suggesting asthma
• Peak Expiratory Flow Rate: Measures severity during exacerbations
• DLCO (Diffusing capacity): Rarely performs, but can be helpful

Treatment Strategies

1. Intermittent Asthma: Short-acting bronchodilator (e.g., Albuterol) PRN
2. Persistent Asthma: Stepwise Approach: Increasing Severity of Treatment:
   • Low-dose Inhaled Corticosteroid (ICS)
   • Medium-dose ICS or combination with Long-Acting Bronchodilator (LABA)
   • High-dose ICS with LABA
   • Add oral corticosteroid for severe cases
   • Consider specific treatments for certain conditions (Leukotriene receptor antagonist, etc.)
3. Severe Exacerbations:
   • Use short-acting bronchodilator (SABA) and muscarinic antagonist (SAMA, e.g., Ipratropium)
   • IV Magnesium for smooth muscle relaxation
   • Systemic corticosteroids (PO or IV)
   • Non-invasive ventilation (e.g., BiPAP) before considering intubation
   • Ketamine for relaxation and bronchodilation, to avoid intubation

Conclusion

• Recap of important points about asthma pathophysiology, diagnostics, and treatment
• Encourage further study and exams preparation.