Dyspnea (Shortness of Breath): Definition, Pathophysiology, and Clinical Approach

Dyspnea (Greek dyspnoia "disordered breathing") is the subjective experience of breathing discomfort—a sensation of insufficient air, increased work of breathing, or chest tightness. It is a symptom, not a sign; the patient's perception is paramount.

Pathophysiologic Mechanisms

• Increased respiratory drive (hypercapnia, hypoxia, acidosis, exercise, sepsis).
• Increased mechanical load (airway obstruction, reduced compliance, chest wall restriction, weakness).
• Afferent mismatch — discrepancy between central motor output and sensory feedback (chemoreceptors, mechanoreceptors, cortical awareness).

Common Etiologies by System

System	Key Causes
Pulmonary	COPD, asthma, pneumonia, PE, pneumothorax, ILD, pleural effusion
Cardiac	Acute decompensated HF, MI, tamponade, valvular disease, arrhythmia
Hematologic	Severe anemia
Metabolic	DKA, sepsis, salicylate toxicity
Neuromuscular	Myasthenia, Guillain-Barré, phrenic nerve injury
Psychogenic	Anxiety, panic disorder, hyperventilation syndrome

Acute Assessment (ABCDE)

1. Airway / Breathing: SpO₂, RR, accessory muscles, tracheal position, breath sounds.
2. Circulation: BP, HR, JVP, edema, ECG.
3. Disability: GCS, alertness.
4. Exposure: Temperature, skin signs.

Initial Workup

• ABG / VBG (pH, PaCO₂, PaO₂, lactate)
• CXR (portable if unstable)
• ECG, troponin, BNP/NT-proBNP
• CBC, BMP, D-dimer (if PE suspected)
• POCUS (lung, cardiac, IVC, pleural)

Management Principles

• Oxygen to target SpO₂ 92–96% (88–92% if COPD/hypercapnic risk).
• Treat underlying cause (bronchodilators, diuretics, antibiotics, anticoagulation, NIV, intubation).
• Opioids (low-dose morphine) for refractory dyspnea in palliative setting.
• Non-pharmacologic: positioning, fan to face, breathing techniques, anxiety reduction.

Dyspnea is a medical emergency until proven otherwise—rapid, systematic evaluation saves lives.