Critical Care Monitoring - End-Tidal CO₂

• End-tidal CO₂ (ETCO₂) monitoring is used to verify ETT placement, monitor procedural sedation, traumatic brain injury, and to estimate prognosis during cardiopulmonary resuscitation
• ETCO₂ concentration typically underestimates P_aCO₂ by 4-5 mmHg in healthy non-intubated patients
• This relationship is less reliable in critically ill patients secondary to shunt, altered alveolar dead space, and inadequate ventilation
• While a low ETCO₂ value is less useful in the critically ill, a high value almost always correlates with an equal or higher P_aCO₂ value
• This can be useful when monitoring conditions such as status asthmaticus, CHF, or increased ICPs in which a high ETCO₂ may signal the need for additional aggressive treatment