Hyperventilation Syndrome

• Epidemiology & Risk Factors
  • Female > Male (most common in young adults).
  • Strong association w/ underlying psychiatric conditions (e.g., panic disorder, GAD, somatic symptom disorder, MDD).
  • Triggered by acute emotional stress, panic, or physical trauma.
• Clinical Features
  • Respiratory: Tachypnea, hyperpnea (deep sighing breaths), subjective dyspnea, dry mouth.
  • Neurologic: Perioral and acral (fingertips/toes) paresthesias, lightheadedness, dizziness, syncope (due to hypocapnia-induced cerebral vasoconstriction).
  • Musculoskeletal: Carpopedal spasm (painful flexion of wrist/MCP joints, extension of IP joints) due to hypocalcemia-like physiologic state.
  • Cardiovascular: Atypical chest tightness/pain, palpitations.
• Diagnosis
  • Initial/Screening: Clinical diagnosis of exclusion. Pulse oximetry (typically 98-100% on RA).
  • Key Labs:
    • ABG: Acute respiratory alkalosis (↑ pH, ↓ ${\text{PaCO}}_2$, normal ${\text{HCO}}_3^{-}$).
    • BMP: Normal total calcium, but ↓ ionized calcium (alkalosis causes ${\text{H}}^{+}$ to dissociate from albumin, allowing more ${\text{Ca}}^{2+}$ to bind to albumin).
  • Imaging & Diagnostics:
    • CXR: Normal (rules out pneumothorax, pneumonia).
    • ECG: Sinus tachycardia (rules out acute coronary syndrome [ACS]; may show non-specific T-wave abnormalities).
• Differential Diagnostics
  • Pulmonary Embolism (PE): Diff by hypoxemia (↓ ${\text{PaO}}_2$ on ABG), elevated D-dimer, positive Wells criteria. Does not correct with breathing exercises.
  • Asthma/COPD Exacerbation: Diff by expiratory wheezing on auscultation, prolonged expiratory phase, and ↓ peak expiratory flow rate.
  • Salicylate Toxicity: Diff by presence of tinnitus, mixed respiratory alkalosis AND anion gap metabolic acidosis, and elevated serum salicylate levels.
  • Acute Coronary Syndrome (ACS): Diff by exertional chest pain radiation, troponin elevation, and ischemic ECG changes (ST elevations/depressions).
• Management
  • 1st-Line (Acute): Calm reassurance and breathing coaching (diaphragmatic breathing or pursed-lip breathing).
    • Note: Avoid paper bag rebreathing on the USMLE, as it can cause dangerous hypoxia if the patient has a misdiagnosed organic disease (e.g., PE, MI). c
  • 2nd-Line (Acute/Refractory): Short-acting benzodiazepines (e.g., Lorazepam, Alprazolam) if breathing coaching fails and anxiety is severe.
  • Long-term/Maintenance: CBT and SSRIs (e.g., Sertraline) for underlying panic/anxiety disorders.
• Complications
  • Syncope (self-limiting; restores normal breathing pattern).
  • Severe respiratory alkalosis-induced hypokalemia.
  • Cardiac arrhythmias (rare, secondary to severe hypokalemia/alkalosis in pts w/ underlying heart disease).