Refractory Hypercapnia

Refractory Hypercapnia – Amelia Muhs

Background

  • 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)
 


Evaluation

  • Physical exam, mental status, recent medications
  • ABG or VBG – if áPCO2 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

1.  Special considerations

  • If history of OSA, make sure they are on home CPAP/BiPAP
  • If opiate related trial narcan
  • Bronchodilators for reactive airway diseases

2.  BiPAP

  • Contraindicated if pt unable to remove BiPAP mask on their own
  • Increase MV by increasing Δ between IPAP/EPAP or increasing RR

3.  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
  • We generally use volume control modes (i.e. VC/AC) VUMC medicine residents and MICU staff tend to be most familiar with this mode
    • Volume control guarantees a MV
    • NOTE: PRVC is actually a pressure-control mode, does NOT guarantee MV
  • Increase RR
    • 30-35 is about as high as you can go
    • Need to keep in mind I/E time avoids breath stacking/autoPEEP
    • AutoPEEP = gas trapped in the 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)

4. 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