End Tidal CO2; Roadside to Resus

End Tidal CO2 monitoring serves as a critical, non-invasive tool for assessing ventilation and cardiac output in emergency and critical care settings. While frequently used to confirm airway device placement, its utility extends to evaluating the efficacy of chest compressions during cardiac arrest and guiding ventilator adjustments in non-arrest patients. Accurate interpretation requires understanding the four phases of the capnogram—inspiratory baseline, expiratory upstroke, alveolar plateau, and inspiratory downstroke—and recognizing that readings are influenced by metabolism, ventilation, and circulation. Clinicians must account for potential confounders, such as airway leaks or poor perfusion, which create discrepancies between end tidal and arterial CO2 levels. Although valuable for monitoring respiratory rates in spontaneously breathing patients, end tidal CO2 should not function as a standalone diagnostic marker for conditions like DKA or sepsis, but rather as an adjunct to comprehensive clinical assessment.