What are the recommended target end‑tidal CO₂ values and how should abnormal readings be managed in an intubated adult patient?

End-Tidal CO₂ Monitoring in Intubated Adults

Target normocapnia with end-tidal CO₂ of 35-45 mmHg (4.7-6.0 kPa) in mechanically ventilated adults, and always confirm this with arterial blood gas measurements rather than relying on ETCO₂ alone for ventilation management. 1

Target Values

The most recent European Resuscitation Council guidelines (2025) provide clear targets for mechanically ventilated patients:

• Normal range: 35-45 mmHg (4.7-6.0 kPa) 1
• This applies specifically to adults with return of spontaneous circulation after cardiac arrest
• The goal is normocapnia—avoiding both hypocapnia and hypercapnia

For prehospital and emergency intubation, aim for normocapnia equivalent to ETCO₂ of 4.0-4.5 kPa 2

Critical Monitoring Requirements

Always obtain arterial blood gases in addition to monitoring ETCO₂ 1. This is essential because:

• ETCO₂ correlates poorly with actual PaCO₂ in critically ill patients (R² = 0.14 in one study) 3
• Trauma patients show particularly poor correlation, especially those with impaired tissue perfusion 4
• Patients ventilated to "normal" ETCO₂ (35-40 mmHg) were actually hypoventilated (PaCO₂ >40) 80% of the time 4

Management of Abnormal Readings

Low ETCO₂ (<30-35 mmHg)

Low ETCO₂ indicates either inadequate cardiac output or hyperventilation:

• In cardiac arrest: ETCO₂ <10 mmHg suggests inadequate CPR quality and low probability of survival 5, 6
• In intubated trauma patients: ETCO₂ ≤28 mmHg associated with 55% mortality vs 17% with higher values 3
• Action steps:
  • Check arterial blood gas immediately to determine true PaCO₂
  • If PaCO₂ is also low: reduce minute ventilation
  • If PaCO₂ is normal/high despite low ETCO₂: this indicates V/Q mismatch, poor perfusion, or increased dead space
  • Address underlying perfusion issues (fluid resuscitation, vasopressors as needed)
  • Aim to maintain ETCO₂ ≥29 mmHg and arterial-to-ETCO₂ gradient ≤7 mmHg 3

High ETCO₂ (>45 mmHg)

High ETCO₂ suggests hypoventilation:

• Verify with arterial blood gas
• Increase minute ventilation (increase respiratory rate or tidal volume)
• Check for equipment malfunction or circuit issues
• In hypothermic patients, monitor PaCO₂ frequently as hypocapnia may occur despite normal ETCO₂ 1

Sudden Increase in ETCO₂

An abrupt sustained increase to 35-40 mmHg during CPR indicates return of spontaneous circulation 5, 7. This is a reliable indicator of ROSC and should prompt rhythm assessment.

Special Populations

Post-Cardiac Arrest

• Target normocapnia: 35-45 mmHg 1
• Use lung-protective ventilation: 6-8 mL/kg ideal body weight 1
• Monitor frequently if hypothermia is used

Trauma Patients

• Do not rely on ETCO₂ alone—correlation with PaCO₂ is particularly poor 4
• Nearly 50% of prehospital intubated patients arrive with abnormal ETCO₂ 8
• Abnormal initial ETCO₂ associated with 6-fold increased mortality risk 8

COPD/Hypercapnic Patients

• Use supplemental oxygen cautiously 9
• Monitor blood or ETCO₂ levels whenever possible 9
• Assess whether hypoxemia is due to hypoventilation, atelectasis, or secretions 9

Common Pitfalls

1. Assuming ETCO₂ equals PaCO₂: The arterial-to-ETCO₂ gradient can be substantial, especially in critically ill patients with V/Q mismatch
2. Ignoring sudden changes: Abrupt increases suggest ROSC; sudden decreases may indicate circuit disconnect, tube displacement, or cardiovascular collapse
3. Over-reliance in trauma: ETCO₂ has the worst correlation in patients with poor tissue perfusion 4
4. Not accounting for vasopressors: High-dose epinephrine can transiently decrease ETCO₂ despite adequate CPR 5
5. Ignoring sodium bicarbonate effect: Bicarbonate administration causes transient ETCO₂ increase that doesn't reflect improved perfusion 5

Practical Algorithm

1. Initial setup: Confirm tube placement with waveform capnography 1, 2
2. Set initial ventilation: Target ETCO₂ 35-45 mmHg
3. Obtain arterial blood gas within 30-60 minutes 1
4. Adjust ventilation based on PaCO₂, not ETCO₂ alone
5. Recheck blood gases after any significant change in ventilator settings or clinical status
6. Monitor ETCO₂ trends for sudden changes indicating clinical events

1, 5, 7, 2, 3, 8, 4