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Refractory Hypercapnia

Amelia Muhs


  • Inadequate clearance of CO2 leading to respiratory acidosis (pH ≤ 7.20) despite maximum RR&TV (i.e. minute ventilation) tolerated without causing barotrauma or autoPEEP
  • Common causes:
    • Obstructive lung disease (COPD, emphysema, asthma)
    • Hypoventilation (sleep apnea, obesity, sedative medications (ie opiates), neuromuscular weakness, chest wall trauma, ascites/pleural effusion)
    • Increased CO2 load (shock, sepsis, malignant hyperthermia)
  • Presentation:
    • Shortness of breath
    • AMS, somnolence
    • Hypoxemia
    • Tachycardia, hypertension (in some cases)


  • Physical exam, mental status, recent medications
  • ABG or VBG – if increased PCO2 and normal pH, always treat the pH and not the PCO2 (i.e., may be compensated chronic hypercarbia and blowing off more CO2 may be harmful)

Management Algorithm

  • Special considerations
    • If history of OSA, make sure they are on home CPAP/BiPAP
    • If opiate related trial narcan
    • Bronchodilators for reactive airway diseases
  • BiPAP
    • Contraindicated if pt unable to remove BiPAP mask on their own
    • Increase MV by increasing Δ between IPAP/EPAP or increasing RR
  • Mechanical ventilation
    • Allows you to control rate and tidal volume (in Volume Control modes)
    • NOTE: some pts have higher minute ventilation on their own compared to mechanical ventilation (e.g., DKA); pt-specific considerations regarding intubation
    • To increase minute ventilation and CO2 clearance:
      • Increase RR
        • 30-35 is about as high as you can go
        • Need to keep in mind I/E time to avoid breath stacking/autoPEEP (gas trapped in lungs)
        • Some signs of autoPEEP include worsening hypotension and the expiratory limb on the flow waveform on the vent not returning to zero
      • Increase TV we usually start at 4-6mL/kg IBW. You can consider increasing to 8mL/kg IBW as long as plateau pressures remain \< 30 cm H2O
        • Goal peak pressures ≤ 35 cm H2O / plateau pressures ≤ 30 cm H2O
  • ARDS permissive hypercapnia (goal pH ≥ 7.2)
  • V-V ECMO / Extracorporeal carbon dioxide removal (ECCO2R)
  • Indications for hypercapnia:
    • Severe dynamic hyperinflation and/or severe respiratory acidosis
    • pH ≤ 7.25 with PaCO2 ≥ 60 for 6 hr with RR at 35/min and TV increased to target maximum MV while keeping plateau pressure ≤ 32 cm H2O
    • Similar considerations and contraindications as refractory hypoxemia (see above)
    • Benefits: Reduces work of breathing, promotes early ventilator weaning/extubating allows early mobilization and recovery

Last update: 2022-06-02 13:28:55