Dyspnea

Description

• Describes a symptom of many possible underlying diseases
• May or may not correlate with signs of increased work of breathing
• Usually an unconscious activity, dyspnea is the subjective sensation of breathing, from mild discomfort to feelings of suffocation
• Accounts for 3.5% of ED visits
• Caused by difficulties in maintaining homeostasis with respect to gas exchange and acid–base status
• Can reflect an impairment in ventilation, perfusion, metabolic function, or CNS drive
• Mechanisms that control breathing:
  • Control centers:
    • Brainstem and cerebral cortex affect both automatic and voluntary control of breathing
  • Chemo, stretch, and irritant sensors:
    • CO₂ receptors located centrally and PO₂ receptors located peripherally
    • Mechanoreceptors lie in respiratory muscles and respond to stretch
    • Intrapulmonary mechanoreceptors respond to chemical irritation, engorgement, and stretch
  • Effectors of respiratory center output are in the respiratory muscles and respond to central stimulation to move air in and out of the thoracic cavity
  • Motor–sensory control of the diaphragm and muscles of respiration are controlled by C3–C8 nerves and T1–T12 nerves
• Derangements of any of these neurosensory pathways produces dyspnea:
  • Many etiologies for the sensation of dyspnea are due to the complex nature of mechanisms that control breathing

Etiology

• Upper airway:
  • Epiglottitis
  • Laryngeal obstruction
  • Tracheitis or tracheobronchitis
  • Angioedema
• Pulmonary:
  • Airway mass
  • Asthma
  • Bronchitis
  • Chest wall trauma
  • CHF
  • Drug-induced conditions (e.g., crack lung, aspirin overdose)
  • Effusion
  • Emphysema
  • Lung cancer
  • Metastatic disease
  • Pneumonia
  • Pneumothorax
  • Pulmonary embolism (PE)
  • Pulmonary HTN
  • Restrictive lung disease
• Cardiovascular:
  • Arrhythmia
  • Coronary artery disease
  • Intracardiac shunt
  • Left ventricular failure
  • Myxoma
  • Pericardial disease
  • Valvular disease
• Neuromuscular:
  • CNS disorders
  • Myopathy and neuropathy
  • Phrenic nerve and diaphragmatic disorders
  • Spinal cord disorders
  • Head and cervical spine trauma
  • Systemic neuromuscular disorders
• Metabolic acidosis:
  • Sepsis
  • Ketoacidosis (diabetic, alcoholic, starvation)
  • Renal failure (volume overload, uremia)
  • Profound thiamine deficiency
• Toxic:
  • Methemoglobinemia
  • Salicylate poisoning
  • Cellular asphyxiants:
    • Carbon monoxide
    • Cyanide
    • Hydrogen sulfide
    • Sodium azide
  • Toxic alcohols
• Abdominal compression:
  • Ascites
  • Pregnancy
  • Massive obesity
• Psychogenic:
  • Hyperventilation
  • Anxiety
• Other:
  • Altitude
  • Anaphylaxis
  • Anemia

• Most common diagnoses in elderly patients presenting to the ED with dyspnea:
  • Decompensated heart failure
  • Infection (pneumonia, UTI)
  • COPD/asthma
  • PE

• Common differential diagnosis for age <2 yr:
  • Asthma
  • Croup
  • Congenital anomalies of the airway
  • Congenital heart disease
  • Foreign-body aspiration
  • Nasopharyngeal obstruction
  • Shock

• Pregnant women have decreased lung capacity and a propensity for anemia
• While supine, the gravid uterus can compress the IVC, leading to dyspnea and hypotension
• There is an increased risk for PE throughout and shortly after pregnancy, as well as for amniotic fluid emboli in the peripartum and postpartum periods