3.1 Asthma & Chronic Obstructive Pulmonary Disease Exacerbations

Pathophysiological Divergence: Asthma vs. COPD

Acute exacerbations of obstructive airway disease represent frequent, high-stakes medical emergencies encountered across Caribbean inpatient wards and casualty departments. Although both conditions present with dyspnea, wheezing, and cough, their underlying pathophysiology dictates fundamentally different resuscitation strategies.

• Asthma is characterized by chronic eosinophilic airway inflammation, mast cell activation, T-helper 2 (Th2) cytokine release (interleukins IL-4, IL-5, and IL-13), and hyperresponsiveness of bronchial smooth muscle. Airflow limitation is predominantly dynamic, episodic, and reversible following bronchodilator therapy or systemic corticosteroids.
• Chronic Obstructive Pulmonary Disease (COPD) is characterized by progressive, predominantly irreversible airflow limitation caused by small airway disease (obstructive bronchiolitis) and parenchymal destruction (emphysema). Inflammation is primarily neutrophilic and CD8+ T-lymphocyte-driven, initiated by chronic noxious particle exposure—most commonly tobacco smoke, occupational dusts, or indoor biomass smoke from traditional cooking methods in rural territories.

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Acute Asthma Exacerbation: Clinical Severity Stratification

Accurate classification of asthma severity determines the aggressiveness of pharmacological intervention and the disposition of the patient. Objective assessment using peak expiratory flow rate (PEFR), arterial blood gas (ABG) analysis, and vital signs is essential because subjective symptoms and chest auscultation notoriously underestimate clinical severity.

Severity Categories in Adults

1. Moderate Exacerbation:

   • Increasing symptoms, cough, mild wheeze
   • PEFR 50% to 75% of best or predicted
   • Respiratory rate < 25 breaths/min; heart rate < 110 bpm
   • Ability to speak in full sentences; no accessory muscle use
   • Oxygen saturation (SpO2) >= 92% on room air

2. Severe Asthma:

   • PEFR 33% to 50% of best or predicted
   • Respiratory rate >= 25 breaths/min
   • Heart rate >= 110 bpm
   • Inability to complete sentences in one breath; marked accessory sternocleidomastoid use
   • Pulsus paradoxus may be present (systolic fall > 10 mmHg during inspiration)

3. Life-Threatening Asthma (Any One Feature Qualifies):

   • PEFR < 33% of best or predicted
   • Silent chest on auscultation (minimal air entry due to extreme airway narrowing)
   • Cyanosis, feeble respiratory effort, or patient exhaustion
   • Bradycardia, hypotension, or cardiac dysrhythmias
   • Confusion, delirium, agitation, or coma
   • Normal PaCO2 (4.6–6.0 kPa; 35–45 mmHg) or a higher value: In a tachypneic patient, hyperventilation should cause hypocapnia. A 'normal' PaCO2 signals respiratory muscle fatigue and impending respiratory arrest.
   • Severe hypoxemia: PaO2 < 8.0 kPa (60 mmHg) or SpO2 < 92%, irrespective of oxygen treatment
   • Low pH (respiratory and/or lactic acidosis)

4. Near-Fatal Asthma:

   • Raised PaCO2 and/or a requirement for mechanical ventilation with raised inflation pressures.

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Stepwise Emergency Pharmacotherapy for Acute Asthma

Emergency management prioritizes reversing bronchospasm, correcting hypoxemia, and blunting airway inflammation.

Step 1: Titrated Oxygen for Hypoxaemia

• If hypoxaemic, titrate supplemental oxygen to SpO2 93% to 95% in adults; use the age- or pregnancy-specific local target for children and pregnant patients. Select the device and flow needed to reach the target.
• Clinical Pearl: Correct hypoxaemia promptly, but avoid uncontrolled high-concentration oxygen: excessive oxygen can raise PaCO2 in acute asthma. Titrate oxygen and reassess clinical status and blood gases when indicated.

Step 2: Inhaled Bronchodilators

• Short-Acting Beta-2 Agonist (SABA): Salbutamol (albuterol) 5 mg nebulized with oxygen (or 4 to 10 puffs via metered-dose inhaler with a large-volume spacer every 15-20 minutes during the first hour). In severe or life-threatening cases, administer back-to-back or continuous nebulization (10-15 mg/hr).
• Short-Acting Muscarinic Antagonist (SAMA): Ipratropium bromide 0.5 mg nebulized combined with salbutamol every 20 minutes for 3 doses, then every 4 to 6 hours. Co-administration provides synergistic bronchodilation and reduces hospital admission rates.

Step 3: Systemic Corticosteroids

• Corticosteroids accelerate the resolution of airway mucosal edema and restore beta-adrenergic receptor responsiveness.
• Administer oral prednisolone 40 mg to 50 mg daily (or intravenous hydrocortisone 100 mg every 6 hours if the patient is vomiting, exhausted, or unable to swallow).
• Continue systemic steroids for at least 5 days or until full resolution. Tapering is unnecessary for courses lasting fewer than 14 days.

Step 4: Intravenous Magnesium Sulfate (Second-Line Resuscitation)

• Indicated for severe acute asthma failing to respond promptly to nebulized bronchodilators, or any patient presenting with life-threatening features.
• Administer magnesium sulfate 1.2 g to 2.0 g IV infusion over 20 minutes (diluted in 100 mL 0.9% saline).
• Mechanism: Inhibits smooth muscle voltage-gated calcium channels, blocks acetylcholine release at the motor end-plate, and enhances beta-agonist bronchodilation.

Intensive Care and Mechanical Ventilation Indications

• Transfer to the ICU and prepare for rapid sequence intubation (RSI) if the patient exhibits:
  • Deteriorating level of consciousness, exhaustion, or respiratory arrest
  • Rising PaCO2 and progressive respiratory acidosis (pH < 7.25)
  • Refractory severe hypoxemia (PaO2 < 8.0 kPa) despite maximal non-invasive therapy
• Caution: Non-invasive positive pressure ventilation (BiPAP/CPAP) has no established role in acute asthma and can cause barotrauma (pneumothorax, pneumomediastinum). Invasive ventilation requires low tidal volumes (6 mL/kg), slow respiratory rates, and prolonged expiratory times to minimize dynamic hyperinflation and auto-PEEP ('breath stacking').

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Acute Exacerbation of COPD (AECOPD)

An acute exacerbation of COPD is defined as an acute worsening of respiratory symptoms that results in additional therapy. The primary triggers are respiratory tract infections (70-80% of cases) and environmental irritants.

Infective Etiology

• Bacterial Pathogens (50%): Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis, and, in patients with severe baseline obstruction (FEV1 < 30%) or frequent hospitalizations, Pseudomonas aeruginosa.
• Viral Pathogens (30-50%): Human rhinovirus, influenza, respiratory syncytial virus (RSV), and parainfluenza.

Controlled Oxygen Therapy & Hypercapnic Respiratory Failure

In severe COPD, excessive uncontrolled oxygen delivery can precipitate lethal acute-on-chronic hypercapnic respiratory failure and CO2 narcosis through several physiological mechanisms, including:

1. Worsening Ventilation-Perfusion (V/Q) Mismatch: High-concentration oxygen reverses hypoxic pulmonary vasoconstriction, increasing blood flow to poorly ventilated alveolar units and worsening V/Q matching and CO2 elimination.
2. The Haldane Effect: Deoxygenated hemoglobin binds CO2 with higher affinity than oxygenated hemoglobin. Flooding the circulation with oxygen displaces CO2 from hemoglobin into plasma, acutely elevating PaCO2.
3. Ventilatory Change: Oxygen may reduce ventilation in some patients, but loss of hypoxic drive is not the sole explanation for oxygen-induced hypercapnia. V/Q mismatch and altered CO2 carriage remain important; treat hypoxaemia with controlled oxygen.

• Oxygen Target: Administer controlled oxygen via a 24% or 28% Venturi mask to achieve an SpO2 of 88% to 92%. Use air-driven nebulizers in hypercapnic/risk patients, with separate oxygen titrated to 88–92%. If only oxygen-driven nebulization is available, limit treatment to about 6 minutes, monitor SpO2 continuously and promptly resume controlled oxygen. Recheck blood gases within 30–60 minutes.

Pharmacological Management

• Bronchodilators: Nebulized salbutamol 2.5-5 mg plus ipratropium bromide 0.5 mg every 4-6 hours.
• Systemic Corticosteroids: Oral prednisolone 30 mg to 40 mg once daily for 5 days. The REDUCE trial found 5 days of prednisone 40 mg daily non-inferior to 14 days for re-exacerbation, with lower cumulative steroid exposure; measured adverse reactions did not differ significantly.
• Antibiotic Indications (The Anthonisen Criteria):
  • Cardinal symptoms: (1) Increased dyspnea, (2) Increased sputum volume, (3) Increased sputum purulence.
  • Type 1 (Severe): All three cardinal symptoms present -> Antibiotics definitely indicated.
  • Type 2: Two cardinal symptoms present (must include increased sputum purulence) -> Antibiotics indicated.
  • Type 3: One cardinal symptom plus another feature (e.g. fever, wheeze, recent URTI). Hospitalization alone does not mandate antibiotics. Antibiotics are also indicated when invasive/NIV support is required or prior exacerbations had positive sputum bacterial cultures.
  • First-Line Antibiotics: Amoxicillin 500 mg TDS, doxycycline 100 mg BD, or azithromycin 500 mg on day 1, then 250 mg daily on days 2–5. For patients at high risk of Pseudomonas, prescribe oral ciprofloxacin 500-750 mg BD or intravenous antipseudomonal agents.

Non-Invasive Ventilation (NIV / BiPAP)

NIV is the standard of care for acute hypercapnic respiratory failure in AECOPD.

• Indications: Persistent acute or acute-on-chronic respiratory acidosis (pH <=7.35 and PaCO2 >=6.0 kPa / 45 mmHg) despite initial optimal treatment, usually reassessed within 1 hour. pH <7.25 warrants urgent critical-care review and close monitoring, not automatic exclusion from NIV; do not delay escalation in a deteriorating patient.
• Settings: Inspiratory Positive Airway Pressure (IPAP) started at 10-12 cmH2O (titrated up to 16-20 cmH2O); Expiratory Positive Airway Pressure (EPAP) 4-5 cmH2O; backup respiratory rate 12-15 breaths/min.
• Contraindications: Respiratory arrest, severe hemodynamic instability, severe facial trauma/burns, bowel obstruction/vomiting (aspiration risk), inability to protect the airway or cooperate safely, or undrained pneumothorax.

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Comparison: Acute Asthma vs. COPD Exacerbation Management