Is a partial pressure of carbon dioxide (PCO2) of 70 mmHg an indication for intubation?

PCO2 of 70 mmHg as an Indication for Intubation

A PCO2 of 70 mmHg alone is not an absolute indication for intubation, but it is a concerning value that requires careful assessment of the patient's overall clinical status, particularly their level of consciousness, work of breathing, and pH. The decision to intubate should be based on a combination of clinical factors rather than a single PCO2 value.

Clinical Assessment Algorithm for Intubation Decision

Immediate Indications for Intubation

• Respiratory arrest or imminent respiratory arrest
• Severe respiratory distress with inability to maintain airway
• Depressed consciousness (Glasgow Coma Score <8)
• pH <7.15 despite optimal non-invasive ventilation (NIV) attempts 1
• Inability to clear secretions

Assessment of PCO2 of 70 mmHg in Context

1. Evaluate pH and Respiratory Status:

   • If pH <7.25: Consider NIV trial if no contraindications exist
   • If pH <7.15: Strong indication for intubation 1
   • If respiratory rate >35 breaths/min: Consider intubation 1

2. Assess Response to Non-Invasive Ventilation (if appropriate):

   • Trial NIV if no immediate need for intubation
   • Failure indicators during NIV trial:
     • No improvement in respiratory rate and oxygenation within 1-2 hours 1
     • No decrease in PCO2 in patients with initial hypercapnia 1
     • Tidal volume >9.5 ml/kg predicted body weight during NIV 1, 2

3. Evaluate for Contraindications to NIV:

   • Cardiovascular instability/shock
   • Impaired mental status/inability to cooperate
   • High aspiration risk
   • Facial trauma or abnormalities preventing mask seal

Special Considerations by Underlying Condition

COPD Patients

• In COPD exacerbations, PCO2 of 70 mmHg may be tolerated if:
  • pH is >7.25
  • Patient is alert and able to protect airway
  • Work of breathing is not excessive
  • Patient is responding to NIV 1

Acute Hypoxemic Respiratory Failure

• PCO2 of 70 mmHg with hypoxemia (PaO2/FiO2 <150) and bilateral infiltrates suggests severe respiratory failure
• Higher risk of NIV failure; consider early intubation 1
• Delayed intubation in COVID-19 ARDS is associated with increased mortality 3

Neuromuscular Disorders or CNS Depression

• Lower threshold for intubation with PCO2 of 70 mmHg
• Impaired respiratory drive or muscle weakness limits compensation

Monitoring During Decision-Making

• Continuous monitoring of:
  • Mental status
  • Work of breathing
  • Arterial blood gases (not just PCO2, but pH and PaO2)
  • Oxygen saturation
  • Hemodynamic stability

Important Caveats

• End-tidal CO2 may not reliably reflect PaCO2 in critically ill patients; arterial blood gas measurement is preferred 4
• Increasing respiratory rate alone may not improve CO2 clearance and can worsen dynamic hyperinflation in some patients 5
• Delaying necessary intubation can increase mortality, particularly in patients with ARDS 3
• High respiratory rate (>30 breaths/min) on standard oxygen therapy is associated with higher likelihood of needing intubation 2

Conclusion

While a PCO2 of 70 mmHg is concerning and warrants close attention, the decision to intubate should be based on the overall clinical picture, particularly the patient's mental status, work of breathing, pH, and response to non-invasive ventilation if attempted. In patients with chronic hypercapnia (e.g., COPD), this level may be tolerated if pH is not severely acidotic and the patient is clinically stable.