Chief Complaint: Acute Dyspnea: A Framework for Differential Diagnosis

Acute dyspnea, or shortness of breath, is a common symptom ranging from non-emergent to emergent. Even seemingly benign cases can quickly decompensate, making a systematic approach crucial in time-sensitive settings. When facing a patient experiencing acute dyspnea, just remember to "inhale and follow the oxygen."

This framework helps you think through the differential diagnosis by tracing the flow of oxygen through the body—from the mouth and throat to the lungs, the heart, and finally the body (systemic).

Mouth/Throat

Emergent conditions in this category obstruct airflow and require immediate action. 

• Angioedema: Often linked to allergic reactions; angioedema presents with swelling that can block the airway.
• Epiglottitis: A rare, rapid-onset sore throat, with drooling and stridor. While historically more common in children, it’s now seen more frequently in adults thanks to widespread Hib vaccination.

Lungs

Pulmonary causes of dyspnea are varied, ranging from mild to severe:

Non-emergent causes: 

•  Mild-to-moderate asthma or COPD exacerbations
• Pneumonia
• Interstitial lung disease
• Pleural effusions
• Viral illnesses like COVID-19, RSV, and croup 

Emergent, “can’t miss” diagnoses:

• Pulmonary embolism (PE)
• Pneumothorax
• Severe asthma exacerbations

Diagnostic Tip: A chest X-ray is a very useful diagnostic tool to help you rule in or rule out many of these pulmonary differentials. 

Heart

Cardiac-related causes of dyspnea often overlap with pulmonary symptoms and require careful assessment.

• Non-emergent causes:
• Heart Failure
• Valvular Disease
• Arrhythmias 
• Pericarditis

Emergent, “can’t miss” diagnoses:

• Acute coronary syndrome 
• Massive pericardial effusion causing tamponade 

Diagnostic Tip: Look for signs of cardiovascular disease, including peripheral edema, murmurs, and S3 or S4 gallops. 

Diagnostic Tools: Consider EKG, cardiac enzymes, BNP, and echocardiography for patients with suspected cardiac causes.

Body (Systemic)

Not all dyspnea stems from pulmonary or cardiac issues. Systemic conditions can be the underlying culprit.

Non-emergent causes:

• Anxiety or panic attacks
• Hypothyroidism
• Symptomatic anemia

Emergent, “can’t miss” diagnoses:

• Anaphylaxis
• Diabetic ketoacidosiss
• Sepsis
• Neuromuscular Disorder (e.g. Gillian-Barre)

Overdose/Toxicity

Clinical Pearls 

• Pattern Recognition: Acute onset with systemic signs like fever, rash, or hypotension suggests sepsis, anaphylaxis, and angioedema.
• Time Sensitivity: While emergent causes are less common, they cannot be missed. Assess and stabilize immediately.
• Dynamic Assessment: Reassess frequently; non-emergent causes can rapidly worsen.

Acute dyspnea demands a systematic, high-stakes approach. By "inhaling and following the oxygen," you can effectively narrow down the differential, prioritize emergent causes, and guide timely interventions.