What are the investigations for acute exacerbations of Chronic Obstructive Pulmonary Disease (COPD) in terms of confirming the diagnosis, excluding differential diagnoses, identifying risk factors, looking for complications, and monitoring and management?

Investigations for Acute Exacerbations of COPD

The essential investigations for acute exacerbations of COPD include chest radiography to exclude complications like pneumonia or pneumothorax, arterial blood gas analysis for severe exacerbations, sputum culture to identify bacterial pathogens, and basic blood tests to assess inflammatory markers and identify comorbidities. 1

Confirming the Diagnosis

• Increased dyspnea is the key symptom of an exacerbation, often accompanied by increased sputum purulence and volume, increased cough, and wheeze 1
• Clinical assessment should classify exacerbations as:
  • Mild (requiring only short-acting bronchodilators)
  • Moderate (requiring short-acting bronchodilators plus antibiotics and/or oral corticosteroids)
  • Severe (requiring hospitalization or emergency room visits) 1
• Spirometry is not typically recommended during an acute exacerbation as it may be difficult for the patient to perform and results can be misleading 1

Excluding Differential Diagnoses

• Chest radiography is essential to exclude:
  • Pneumonia
  • Pneumothorax
  • Pulmonary edema
  • Lung cancer 1
• Differential diagnoses that must be excluded include:
  • Acute coronary syndrome
  • Worsening congestive heart failure
  • Pulmonary embolism 1
• Additional investigations to consider for differential diagnosis:
  • ECG to rule out cardiac causes
  • D-dimer and CT pulmonary angiography if pulmonary embolism is suspected
  • Echocardiography if heart failure is suspected 2

Identifying Risk Factors

• Assessment of previous exacerbation history (frequency defined as two or more per year indicates high risk) 1
• Evaluation of lung function parameters (worse lung function increases risk) 1
• CT imaging may identify:
  • Increased ratio of pulmonary artery to aorta cross-sectional dimension (ratio > 1)
  • Greater percentage of emphysema or airway wall thickness 1
• Assessment of exercise capacity (lower capacity increases risk) 1
• Evaluation for chronic bronchitis (increases exacerbation risk) 1

Looking for Complications

• Arterial blood gas analysis is crucial in severe exacerbations to:
  • Identify respiratory failure
  • Assess need for oxygen therapy or ventilatory support 1, 2
• Blood tests to evaluate:
  • Complete blood count for infection or polycythemia
  • Electrolytes for metabolic disturbances
  • Renal function 2
• Assessment for cor pulmonale and pulmonary hypertension:
  • Chest radiography (if maximum diameter of right descending pulmonary artery exceeds 16 mm, pulmonary hypertension is likely) 1
  • Echocardiography in selected cases 1

Monitoring and Management

• Sputum culture and sensitivity to guide antibiotic therapy when:
  • Purulent sputum is present
  • Previous ineffective antibiotic treatment
  • Severe exacerbation requiring hospitalization 1, 2
• Blood inflammatory markers:
  • C-reactive protein (elevated ≥3 mg/L during exacerbations)
  • Blood neutrophils or eosinophils (≥9000 neutrophils/mm³ or ≥2% blood eosinophils) 3
• Oxygen saturation monitoring:
  • Continuous pulse oximetry for hospitalized patients
  • Target saturation of 88-92% for those at risk of hypercapnia 1
• Repeat arterial blood gas analysis to monitor:
  • Response to oxygen therapy
  • Development or worsening of respiratory acidosis 2
• Assessment of response to treatment:
  • Improvement in symptoms
  • Oxygen saturation
  • Arterial blood gases if initially abnormal 1

Special Considerations

• High-resolution CT scanning is not recommended for routine assessment during exacerbations but may be useful in:
  • Evaluation of bullae
  • Investigation of coexisting bronchiectasis 1
• Sleep studies (polysomnography) may be indicated if:
  • Coexisting obstructive sleep apnea is suspected
  • Unexplained features such as cor pulmonale or polycythemia despite relatively mild airway obstruction 1
• Quality of life questionnaires, while not routinely used in acute settings, may help assess the impact of exacerbations and response to treatment 1

Follow-up After Exacerbation

• Spirometry is essential during follow-up assessment 1
• If arterial blood gas tensions were abnormal during the exacerbation, they should be monitored during follow-up 1
• Assessment for early recurrence and readmission risk, which are common after exacerbations 4
• Evaluation of maintenance therapy adequacy to prevent future exacerbations 1