Correlation Between Capnography and Arterial Carbon Dioxide Before, During, and After Severe Chest Injury in Swine.

摘要

The relationship between end-tidal carbon dioxide (EtCO2) and arterial carbon dioxide (PaCO2) if better defined could facilitate the difficult task of ventilation in prehospital trauma patients. We aimed to study the PaCO2-EtCO2 relationship before, during, and after chest trauma, hemorrhage, and resuscitation in swine. Twenty-four swine were intubated, anesthetized, and monitored in an animal intensive care unit during three phases: phase 1 (day 1, healthy animals); phase 2 (day 2, injury), which consisted of blunt chest trauma, hemorrhage, and resuscitation; and phase 3 (day 2, after injury). Respiratory maneuvers (changes in respiratory rate and tidal volume [TV], intended to vary the PaCO2 over a range of 25 to 85 mmHg, were performed during phases 1 and 3. End-tidal CO2 and PaCO2 were recorded after each respiratory maneuver and analyzed using linear regression. During phase 1, PaCO2 and EtCO2 were strongly correlated (r 2 0.97, P G 0.01). During phase 2, animals developed decreased oxygenation (PaO2:FiO2 [fraction of inspired oxygen] ratio G200) and hypotension (mean arterial pressure, 20 50 mmHg); the PaCO2-EtCO2 relationship deteriorated (r 2 0.25, P G 0.0001). During phase 3, oxygenation, hemodynamics, and the PaCO2-EtCO2 relationship recovered (r 2 0.92, P G 0.01). End-tidal CO2 closely correlates to PaCO2 in healthy animals and after injury/resuscitation across a wide range of respiratory rates and tidal volumes. Once oxygenation and hemodynamics are restored, EtCO2 can be used to predict PaCO2 following chest trauma/ hemorrhage and should be considered for patient monitoring. This work demonstrated that EtCO2 alone can reliably be used to estimate PaCO2 in uninjured subjects and in those subjects who have been resuscitated from severe injury. Immediately after blunt chest injury, the correlation between EtCO2 and PaCO2 is temporarily unstable.