Refractory Hypercapnia

Lauren Taylor

Background

  • Definition: Persistently elevated PaCO2 with pH < 7.20 despite optimized ventilatory support with strategies to minimize dynamic hyperinflation and autoPEEP.
  • Common causes: 
    • Obstructive lung disease (COPD, emphysema, asthma)
    • Hypoventilation syndromes (congenital central hypoventilation, brainstem injury, sleep apnea, obesity, sedative medications (i.e. opiates), neuromuscular weakness, chest wall trauma, ascites/pleural effusion)
    • Increased CO2 load (shock, sepsis, malignant hyperthermia)

Presentation

  • Shortness of breath, AMS, somnolence, hypoxemia, tachycardia, HTN (in some cases).

Evaluation

  • Physical exam, mental status, recent medications.
  • ABG or VBG - See “Basics of Blood Gases” for guidance on interpretation.

Management

  • Address underlying/reversible causes.
    • If history of OSA, make sure they are on home CPAP/BiPAP.
    • If opiate related, trial Narcan.
    • If reactive airway disease contributing, bronchodilators.

BiPAP

  • See “Modes of Oxygen Delivery” to review basic principles of BiPAP.
  • Increase MV by increasing Δ between IPAP/EPAP or increasing RR.
  • Consider AVAPS for patients with neuromuscular disease, obesity hypoventilation syndrome, COPD with chronic hypercapnia, central sleep apnea, or restrictive thoracic disorders.
  • Average Volume-Assured Pressure Support (AVAPS) is a hybrid NIPPV mode that adjusts IPAP breath-by-breath to ensure a target tidal volume or minute ventilation.

Mechanical ventilation

  • See “Introduction to Vent Management” to review basic principles.
  • To increase MV and CO2 clearance:
    • Increase RR: Up to ~30-35 breaths/min
    • Need to keep in mind I/E time to avoid breath stacking/autoPEEP
    • Evidence of autoPEEP: Increased WOB/vent dyssynchrony, worsening hypotension, and failure of the expiratory limb on the flow waveform on the vent to return to zero.
    • Possible corrective measures: Lower RR, decrease inspiratory time, increase expiratory phase time.
    • Increase TV: Usually start at 4-6mL/kg PBW. Can consider increasing to 8mL/kg PBW as long as plateau pressures remain < 30 cm H2O.
    • Goal peak pressures ≤ 35 cmH2O / plateau pressures ≤ 30 cmH2O.

V-V ECMO / Extracorporeal carbon dioxide removal (ECCO2R)

  • Indications for ECMO for hypercapnia:
    • Severe dynamic hyperinflation and/or severe respiratory acidosis.
    • pH ≤ 7.20 with PaCO2 ≥ 60 mmHg for 6h with RR at 35/min and TV increased to target maximum MV while keeping plateau pressure ≤ 32 cmH2O.
  • See “Refractory Hypoxemia” for further considerations and contraindications.
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