When should Continuous Positive Airway Pressure (CPAP) be considered in acute asthma or Chronic Obstructive Pulmonary Disease (COPD) episodes, and how should it be used with pharmacological therapies like bronchodilators and systemic corticosteroids?

CPAP in Acute Asthma/COPD Exacerbations

CPAP should be considered in COPD exacerbations when there is respiratory acidosis (pH < 7.35) with hypercapnia (PaCO2 > 6-8 kPa) despite optimal medical therapy and oxygen administration, and should be delivered alongside appropriate pharmacological treatments. 1

Indications for CPAP/NPPV in Acute Exacerbations

COPD Exacerbations

• NPPV (typically CPAP plus pressure support ventilation) should be initiated when arterial blood gases show respiratory acidosis (pH < 7.35) with hypercapnia despite optimal medical therapy 1
• More severe acidosis (pH < 7.25) requires NPPV administration in an ICU setting with immediate intubation capability 1
• Respiratory rate > 24 breaths/min with acidosis and hypercapnia is an indication for ventilatory support 1
• A pH below 7.26 is predictive of poor outcome and should prompt consideration of ventilatory support 1

Asthma Exacerbations

• Evidence for CPAP in acute asthma is less established than for COPD 1
• CPAP may be considered in selected asthmatic patients not responding well to medical therapy, as it can decrease respiratory muscle work during acute bronchoconstriction 1
• Failure rate of NIV in asthma has been reported as relatively low (4.7%) in retrospective studies 1

Contraindications for NPPV/CPAP

• Respiratory arrest 1
• Cardiovascular instability (hypotension, arrhythmias, myocardial infarction) 1
• Impaired mental status, somnolence, inability to cooperate 1
• Copious and/or viscous secretions with high aspiration risk 1
• Recent facial or gastro-esophageal surgery 1
• Craniofacial trauma and/or fixed nasopharyngeal abnormality 1
• Burns and extreme obesity 1

CPAP/NPPV Settings and Administration

• CPAP is typically administered at 4-8 cmH2O, often combined with pressure support ventilation (PSV) at 10-15 cmH2O 1
• This combination provides the most effective mode of non-invasive ventilation 1
• NPPV should be delivered in a controlled environment such as intermediate ICUs or high-dependency units 1
• Patients with pH < 7.25 should receive NPPV in the ICU with intubation readily available 1

Concurrent Pharmacological Management

Bronchodilators

• Nebulized bronchodilators should be given on arrival and at 4-6 hourly intervals thereafter 1
• For COPD exacerbations:
  • Moderate exacerbations: β-agonist (salbutamol 2.5-5 mg or terbutaline 5-10 mg) or anticholinergic (ipratropium bromide 0.25-0.5 mg) 1
  • Severe exacerbations: Both β-agonist and anticholinergic should be administered 1
• In patients with COPD and respiratory acidosis, nebulizers should be driven by compressed air rather than oxygen 1
• Supplemental oxygen can be continued via nasal prongs during nebulization (1-2 L/min) 1

Corticosteroids

• Systemic corticosteroids should be administered concurrently (prednisolone 30 mg/day or 100 mg hydrocortisone if oral route not possible) 1
• Typical course is 7-14 days 1

Additional Pharmacological Considerations

• If response to initial bronchodilators is poor, consider intravenous methylxanthines by continuous infusion (aminophylline 0.5 mg/kg per hour) 1
• Appropriate antibiotics should be administered if bacterial infection is suspected 1

Monitoring During CPAP/NPPV

• Arterial blood gases should be measured at baseline and repeated within 60 minutes if the patient is initially acidotic or hypercapnic 1
• Successful NPPV is indicated by:
  • Improvement in ABGs and pH 1
  • Relief of dyspnea 1
  • Resolution of acute episode without need for endotracheal intubation 1
• Continuous monitoring with pulse oximetry is recommended 1

When to Consider Intubation (NPPV Failure)

• Worsening of ABGs and/or pH in 1-2 hours despite NPPV 1
• Lack of improvement in ABGs and/or pH after 4 hours 1
• Severe acidosis (pH < 7.25) and hypercapnia (PaCO2 > 8 kPa/60 mmHg) not improving 1
• Life-threatening hypoxemia (PaO2/FiO2 < 26.6 kPa/200 mmHg) 1
• Tachypnea > 35 breaths/min despite support 1

Clinical Pearls and Pitfalls

• One-year mortality has been reported to be lower in patients receiving NPPV for COPD exacerbations compared to both conventional mechanical ventilation and optimal medical therapy alone 1
• NPPV should be viewed as a form of life support until the underlying cause of acute respiratory failure is reversed with medical therapy 1
• Careful attention to mask fit and patient comfort improves tolerance and effectiveness 1
• Regular assessment of patient-ventilator synchrony is essential 1
• Avoid excessive oxygen administration in COPD patients as it may worsen respiratory acidosis 1, 2