Approach to Acute Dyspnea

Definition and Overview

• Acute dyspnea: Sudden onset of shortness of breath over seconds to about a week.
• Note: Chronic dyspnea can present acutely.
• Framework for dyspnea:
  • Based on organ systems or pathophysiologic mechanisms.

Pathophysiologic Mechanisms

Peripheral Chemoreceptors

• Triggered by hypoxemia, hypercapnia, or acidemia.

Hypoxemia

• Common Causes:
  • Pulmonary edema (cardiogenic or non-cardiogenic)
  • Pneumonia
  • Pulmonary embolism (PE)
  • Pleural effusion
  • COPD exacerbation
• Less Common Causes:
  • Interstitial lung disease
  • Pneumothorax
  • Atelectasis (collapsed lung)
  • Mucus plugging

Hypercapnia

• Causes:
  • Obstructive lung diseases (COPD, severe asthma)
  • Acute neurologic/neuromuscular diseases (myasthenia gravis, transverse myelitis, Guillain-Barre syndrome)
  • Central hypoventilation (drug overdose, obesity hypoventilation syndrome)

Acidemia

• Synergistic with hypercapnia-induced dyspnea.
• Causes without hypercapnia:
  • Metabolic acidosis (e.g., ketoacidosis, lactic acidosis)

Oxygen Delivery to Tissues

• Causes:
  • Anemia
  • Low output heart failure
  • Obstructive shock (massive PE, tamponade, tension pneumothorax)

Miscellaneous Causes

• Myocardial ischemia (angina equivalent)
• Upper airway obstruction (anaphylaxis, angioedema, infections)
• Anxiety/panic attacks
• Acute pain

Practical Diagnostic Approach

Initial Assessment

• History and past medical problems.
• Vital signs.
• Physical exam: Lungs, heart (including jugular venous pressure), extremities.
• Chest x-ray.

Additional Data (if needed)

• CBC, chemistry panel, d-dimer, BNP, procalcitonin, serum lactate, ketones, ABG, ECG, bedside ultrasound, echocardiogram, CT scan.

Key Physical Exam Findings

• Pneumonia: Focal crackles, opacity on x-ray, cough, fever, leukocytosis, elevated procalcitonin.
• Pulmonary Edema: Diffuse crackles, opacities on x-ray, cardiovascular risk factors, elevated JVP, S3, leg swelling, BNP, ECG findings, radiographic clues (pleural effusions, cardiomegaly, Kerley B lines).
• Interstitial Lung Disease (ILD): Diffuse fine crackles, interstitial opacities on x-ray, review medications/exposures, chest CT.
• Pleural Effusion: Unilaterally decreased breath sounds, effusion on x-ray, may need thoracentesis.
• Pneumothorax: Unilaterally decreased breath sounds, obvious on x-ray.
• Asthma/COPD Exacerbation: Bilaterally decreased breath sounds, wheezing, no opacities on x-ray, previous diagnosis, hypercapnia on ABG, hyperinflation on x-ray.

If Lung Exam and Chest X-ray Are Normal but Hypoxemic

• Consider pulmonary embolism (PE).
  • Look for pleuritic chest pain, risk factors (cancer, recent hospitalization, DVT).
  • Use d-dimer, CT angiogram, Well's score.
• Conduct further tests: CBC, metabolic panel, troponin, ABG/VBG, d-dimer, CT angiogram, ECG, pulsus paradoxus check.

Additional Diagnostic Clues

• Onset Speed: Over minutes suggests PE, acute MI, pneumothorax, arrhythmia.
• Respiratory Pattern: Shallow (COPD, asthma, anxiety); Deep (metabolic acidosis, Kussmaul respirations).
• Hypoxemia: Minimal diagnostic impact; do not rule out diagnoses based on normal O2 saturation alone.
• Life-Threatening Diagnoses: PE, acute MI, tamponade, pneumothorax.

Summary

• Etiologies: Categorized by organ system (lungs, heart) or pathophysiologic mechanism.
• Evaluation: Vitals, cardiac/pulmonary/extremity exam, chest x-ray; may need blood tests, ECG, ultrasound, CT scan.
• Hypoxemia: Common but minimally changes differential diagnosis.
• Life-Threatening Diagnoses: Always consider emergent evaluation.