What laboratory studies and management are recommended for a patient with a history of asthma and coronary artery disease (CAD) presenting with progressive shortness of breath?

Laboratory Studies for Progressive Shortness of Breath in Patients with Asthma and Coronary Artery Disease

For patients with a history of asthma and coronary artery disease presenting with progressive shortness of breath, comprehensive laboratory testing should include full blood count, cardiac biomarkers, renal function tests, and assessment of glucose metabolism to evaluate both cardiac and respiratory causes. 1

Initial Laboratory Studies

Essential Blood Tests

• Full blood count including hemoglobin and white cell count 1
• Cardiac biomarkers:
  • Troponin measurements (preferably high-sensitivity assays) to rule out myocardial necrosis 1
  • BNP/NT-proBNP for patients with suspected heart failure 1
• Renal function:
  • Creatinine measurement and estimation of creatinine clearance 1
• Metabolic assessment:
  • HbA1c and fasting plasma glucose (add oral glucose tolerance test if inconclusive) 1
• Thyroid function tests if clinically indicated 1

Additional Tests Based on Clinical Presentation

• Arterial blood gases - particularly important in severe exacerbations to assess oxygenation and acid-base status 2
• Liver function tests - especially if patient is on statin therapy 1
• Creatine kinase - if patient is on statins and complains of myopathy symptoms 1

Diagnostic Imaging and Other Studies

• Chest radiography - to exclude pneumothorax, consolidation, pulmonary edema or other causes of dyspnea 1
• Electrocardiogram (ECG) - to assess for ischemic changes, arrhythmias or other cardiac abnormalities 1
• Echocardiography - recommended for:
  • Excluding alternative causes of angina
  • Identifying regional wall motion abnormalities suggestive of CAD
  • Measuring left ventricular ejection fraction and evaluating diastolic function 1
• Peak expiratory flow (PEF) or spirometry - to assess airflow limitation and response to bronchodilators 2

Management Approach

For Predominant Asthma Symptoms

1. Oxygen therapy - maintain SaO₂ >90% (>95% in pregnant women and patients with heart disease) 2
2. Short-acting beta-agonists (SABAs):
   • Albuterol 2.5 mg via nebulizer every 20-30 minutes for first 3 doses 2
   • For severe exacerbations, consider continuous administration 2
3. Systemic corticosteroids:
   • Prednisone 40-60 mg daily for 5-10 days (no tapering necessary for short courses) 2
   • Oral administration is as effective as intravenous for moderate to severe exacerbations 2
4. Ipratropium bromide in combination with SABAs:
   • 4-8 puffs every 20 minutes via MDI with spacer, or
   • 0.25-0.5 mg every 20 minutes for three doses via nebulization 2
5. Magnesium sulfate for severe refractory asthma:
   • 2g IV administered over 20 minutes 2

For Predominant Cardiac Symptoms

1. Careful consideration of beta-blockers:
   • Non-selective beta-blockers should be avoided in patients with asthma 3
   • Cardio-selective beta-blockers may be used at low doses when strongly indicated 3, 4
2. Coronary evaluation if unstable symptoms or elevated troponin 1, 5

Special Considerations

• Monitor for cardiac complications in patients with uncontrolled asthma, as there is a dose-response relationship between asthma control and myocardial infarction risk 6
• Caution with beta-agonists in patients with CAD, as they may exacerbate cardiac symptoms 4
• Consider coronary vasospasm in asthmatic patients with chest pain, as asthma increases risk of coronary vasospastic angina 7

Monitoring and Follow-up

• Regular monitoring of peak flow and symptoms during acute exacerbations 2
• Annual laboratory assessment for patients with stable CAD:
  • Lipids, glucose metabolism, and creatinine 1
• Discharge criteria for asthma exacerbations:
  • FEV1 or PEF ≥70% of predicted or personal best
  • Minimal or absent symptoms
  • Stable response to bronchodilator therapy for 60 minutes 2

Common Pitfalls to Avoid

• Delaying treatment to obtain laboratory studies in acute asthma exacerbations 2
• Using non-selective beta-blockers in patients with asthma 3
• Overlooking cardiac causes of dyspnea in patients with known asthma 6
• Failing to recognize that asthma and CAD can exacerbate each other through inflammatory pathways 6, 4

By systematically evaluating both cardiac and respiratory causes, clinicians can effectively diagnose and manage progressive shortness of breath in patients with this challenging combination of comorbidities.