In the Field
EtCO2 is the most reliable confirmation that an advanced airway is in the trachea, not the esophagus. A waveform that rises with each ventilation and falls between breaths is in the airway. A flat line is not. Beyond placement confirmation, EtCO2 numbers track perfusion and ventilation in real time. Falling EtCO2 during CPR signals deteriorating cardiac output. Rising EtCO2 during ROSC signals return of perfusion. In TBI, hyperventilation drops EtCO2 and constricts cerebral vessels, which used to be doctrine and is now understood to worsen secondary brain injury.
Common Mistake
Hyperventilating a TBI casualty. The reflex to bag harder when the patient looks worse drops EtCO2 below 30 mmHg, causes cerebral vasoconstriction, and worsens ischemia in already injured brain tissue. TCCC 2026 explicitly targets EtCO2 35 to 45 mmHg in TBI and specifies 10 breaths per minute (one every 6 seconds) when monitoring is unavailable.
Technical Detail
EtCO2 normal range 35 to 45 mmHg in spontaneously breathing patients. Measured by sidestream or mainstream capnography sampling exhaled gas. Capnography produces a waveform plot of CO2 versus time; the plateau represents alveolar gas, and the peak value is EtCO2. Clinical uses: (1) airway placement confirmation (waveform confirms tracheal placement); (2) ventilation rate guidance (target 35 to 45 mmHg); (3) CPR quality (EtCO2 below 10 mmHg suggests inadequate compressions); (4) ROSC detection (sudden rise of 10 mmHg or more during CPR). TCCC 2026 specifies continuous EtCO2 monitoring after cricothyroidotomy and during ventilated TBI management.
