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 PaCO2 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 PaCO2 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
