3.4 Asthma, COPD, & Respiratory Failure (CTS Guidelines)
Key Takeaways
- Canadian Thoracic Society (CTS) asthma guidelines recommend anti-inflammatory reliever therapy (low-dose ICS-formoterol as needed) across all severity steps rather than SABA monotherapy to prevent severe exacerbations.
- Asthma diagnosis requires objective documentation of reversible airflow obstruction: post-bronchodilator FEV1 improvement of ≥12% AND ≥200 mL, or peak expiratory flow (PEF) variability >20%, or positive methacholine challenge (PC20 ≤8 mg/mL).
- COPD diagnosis requires spirometry showing post-bronchodilator FEV1/FVC <0.70; dual LAMA + LABA bronchodilation is preferred initial maintenance therapy for symptomatic patients.
- COPD exacerbation target oxygen saturation is strictly 88-92% to avoid hypercapnic respiratory drive suppression; systemic steroids (prednisone 40 mg for 5 days) and antibiotics (if purulence present) improve recovery.
- Non-Invasive Positive Pressure Ventilation (BiPAP) is first-line intervention for acute hypercapnic respiratory failure (Type II) in COPD with pH 7.25-7.35.
3.4 Asthma, COPD, & Respiratory Failure (CTS Guidelines)
Quick Summary: Asthma diagnosis requires spirometric reversibility (FEV1 increase ≥12% and ≥200 mL). CTS guidelines mandate Anti-Inflammatory Reliever (AIR / SMART) therapy with low-dose ICS-formoterol as needed over SABA monotherapy. COPD diagnosis requires post-bronchodilator FEV1/FVC <0.70; dual LAMA+LABA is first-line. In AECOPD, target SpO2 is 88–92% to avoid CO2 retention, and BiPAP is first-line for hypercapnic respiratory failure.
Asthma Diagnosis & Management (CTS Guidelines)
Asthma is a chronic inflammatory disorder of the airways characterized by hyperresponsiveness, mucosal edema, and variable airflow obstruction.
Objective Diagnostic Criteria
To establish a diagnosis of asthma, clinical symptoms (wheezing, shortness of breath, chest tightness, cough) must be accompanied by objective evidence of variable airflow obstruction:
| Diagnostic Test | Criterion Confirming Asthma Diagnosis |
|---|---|
| Spirometry with Reversibility | Post-bronchodilator (after 200–400 mcg salbutamol) increase in FEV1 of ≥ 12% AND ≥ 200 mL |
| Peak Expiratory Flow (PEF) | Diurnal PEF variability > 20% over a 2-week monitoring period |
| Methacholine Challenge Test | PC20 ≤ 8 mg/mL (provocative concentration causing a 20% drop in FEV1); high negative predictive value |
| Exercise Challenge Test | Post-exercise drop in FEV1 of ≥ 10% AND ≥ 200 mL |
| Fractional Exhaled Nitric Oxide (FeNO) | FeNO > 25–50 ppb supports eosinophilic airway inflammation |
CTS Stepwise Management (SMART / AIR Paradigm)
Critical Guideline Shift: Canadian Thoracic Society (CTS) guidelines state that SABA monotherapy (salbutamol alone) is NO LONGER RECOMMENDED for initial or maintenance asthma management. SABA monotherapy increases severe exacerbation and mortality risk. Instead, anti-inflammatory reliever (AIR) therapy incorporating an Inhaled Corticosteroid (ICS) is mandated across all steps.
- Track 1 (Preferred - Maintenance and Reliever Therapy / MART): Uses a single inhaler containing Low-dose ICS + Formoterol (e.g., Budesonide/Formoterol) as needed for symptom relief in Steps 1–2, and as both daily maintenance AND reliever in Steps 3–4.
- Track 2 (Alternative): SABA (Salbutamol) as needed for symptom relief PLUS regular daily maintenance ICS (low, medium, or high dose).
- Step 5 (Severe Asthma): Add LAMA (Tiotropium) or phenotype-guided Biologics (Anti-IgE: Omalizumab; Anti-IL5/5R: Mepolizumab, Benralizumab; Anti-IL4R: Dupilumab).
Management of Acute Severe Asthma Exacerbations
- Oxygen: Target SpO2 93–95%.
- Inhaled Bronchodilators: Continuous or frequent nebulized SABA (Salbutamol 5 mg) + SAMA (Ipratropium bromide 0.5 mg) q20min for the first hour.
- Systemic Corticosteroids: Oral Prednisone 40–50 mg daily for 5 days (or IV Methylprednisolone 1 mg/kg q6h if unable to tolerate oral).
- IV Magnesium Sulfate: 2 g IV over 20 minutes for severe exacerbations refractory to initial bronchodilators.
COPD Diagnosis & Management (CTS Guidelines)
Chronic Obstructive Pulmonary Disease (COPD) is characterized by persistent, progressive airflow limitation resulting from chronic bronchitis or emphysema, predominantly driven by cigarette smoking.
Diagnosis & Severity Grading
- Diagnostic Threshold: Post-bronchodilator FEV1/FVC < 0.70 (fixed ratio) on spirometry confirms non-reversible airflow obstruction.
- Severity Classification (Based on Post-Bronchodilator FEV1 % Predicted):
- GOLD 1 (Mild): FEV1 ≥ 80% predicted
- GOLD 2 (Moderate): 50% ≤ FEV1 < 80% predicted
- GOLD 3 (Severe): 30% ≤ FEV1 < 50% predicted
- GOLD 4 (Very Severe): FEV1 < 30% predicted
Pharmacotherapy (CTS Guidelines)
- Initial Maintenance Therapy: Dual long-acting bronchodilator therapy with LAMA + LABA (e.g., Tiotropium/Olodaterol or Umeclidinium/Vilanterol) is preferred over monotherapy for patients with moderate-to-severe symptoms (CAT score ≥10 or mMRC ≥2) or a history of exacerbations.
- Triple Therapy (LAMA + LABA + ICS): Recommended for patients who experience persistent exacerbations (≥2 moderate or ≥1 severe hospitalization per year) AND demonstrate blood eosinophil count ≥300 cells/µL.
- Non-Pharmacological Interventions:
- Smoking Cessation: The single most effective intervention to decrease the rate of FEV1 decline.
- Vaccinations: Annual Influenza, Pneumococcal (PNEU-P-20 / PNEU-C-15), RSV, and COVID-19 vaccines.
- Pulmonary Rehabilitation: Indicated for all symptomatic COPD patients.
- Long-Term Oxygen Therapy (LTOT): Indicated if resting PaO2 ≤55 mmHg (SaO2 ≤88%), or PaO2 56–59 mmHg with evidence of cor pulmonale, right heart failure, or secondary polycythemia (hematocrit >55%). Administer ≥15 hours/day.
Acute Exacerbation of COPD (AECOPD)
- Anthonisen Criteria for Antibiotics: (1) Increased dyspnea, (2) Increased sputum volume, (3) Increased sputum purulence. Antibiotics (Amoxicillin, Doxycycline, or Macrolide/Fluoroquinolone) are indicated if purulence + at least 1 other feature is present, or if requiring mechanical ventilation.
- Oxygen Target: Administer controlled low-flow oxygen targeting SpO2 88–92%.
Exam Trap - Oxygen-Induced Hypercapnia: Uncontrolled high-flow O2 in severe COPD can precipitate severe CO2 retention and narcosis through: (1) Attenuation of hypoxic pulmonary vasoconstriction causing worsening V/Q mismatch, (2) The Haldane effect (de-oxygenated hemoglobin binds CO2 with higher affinity; oxygenation displaces CO2 into plasma), and (3) Decreased minute ventilation.
Acute Respiratory Failure (Type I vs. Type II)
| Feature | Type I Respiratory Failure (Hypoxemic) | Type II Respiratory Failure (Hypercapnic) |
|---|---|---|
| Arterial Blood Gas Criteria | PaO2 < 60 mmHg with normal or low PaCO2 | PaCO2 > 45 mmHg with pH < 7.35 |
| Primary Pathophysiology | V/Q Mismatch or Intrapulmonary Shunt | Alveolar Hypoventilation |
| Common Etiologies | Pneumonia, Pulmonary Edema, ARDS, PE, Atelectasis | AECOPD, Severe Asthma, Opioid OD, ALS, Guillain-Barré |
| Initial Management | High-flow O2, High-Flow Nasal Cannula (HFNC), CPAP | Controlled O2 (target 88–92%), BiPAP (NIV) |
Non-Invasive Positive Pressure Ventilation (BiPAP)
- Indications: First-line therapy for acute hypercapnic respiratory failure in AECOPD presenting with respiratory acidosis (pH 7.25–7.35 and PaCO2 >45 mmHg), and acute cardiogenic pulmonary edema.
- Contraindications: Respiratory arrest, uncooperative/encephalopathic patient, severe facial trauma/burns, high aspiration risk (vomiting, impaired airway reflexes), or hemodynamic instability/shock.
A 24-year-old female presents with a 4-month history of episodic shortness of breath and wheezing occurring twice weekly, typically triggered by cold air. She wakes up at night coughing once per month. Spirometry demonstrates an FEV1 of 82% predicted, which increases by 15% and 240 mL following 400 mcg of inhaled salbutamol. According to Canadian Thoracic Society (CTS) guidelines, what is the most appropriate initial controller and reliever strategy?
A 66-year-old male with a 40 pack-year smoking history presents to the emergency department with a 3-day history of worsening dyspnea, increased sputum volume, and purulent green sputum. On examination: RR 28/min, BP 138/84 mmHg, HR 102 bpm, SpO2 84% on room air. Arterial blood gas (ABG) on room air shows: pH 7.28, PaCO2 58 mmHg, PaO2 48 mmHg, and HCO3 27 mEq/L. In addition to inhaled salbutamol/ipratropium, systemic corticosteroids, and antibiotics, what is the most appropriate immediate respiratory support intervention?
A 70-year-old male with severe COPD is brought to the emergency department in a somnolent state. Emergency medical services administered high-flow 100% oxygen via non-rebreather mask during a 30-minute transport. Repeat ABG reveals: pH 7.14, PaCO2 92 mmHg, PaO2 165 mmHg. Which pathophysiological mechanism primarily accounts for the severe acute rise in PaCO2 following high-flow oxygen administration in this patient?