• Christian Martin-Gill, Bradley J Wheeler, Francis X Guyette, and Sarah E Wheeler.
• Department of Emergency Medicine, University of Pittsburgh, Pittsburgh, PA.
• Prehosp Emerg Care. 2024 Nov 15: 1151-15.

ObjectivesEnd-tidal carbon dioxide (EtCO2) monitoring is widely used as a surrogate for the partial pressure of carbon dioxide (PCO2) in critically ill patients receiving manual or mechanical ventilation in prehospital, emergency, and critical care settings. Specific targets for ETCO2 are a key component of Emergency Medical Services (EMS) protocols, especially for specific patient groups such as those with traumatic brain injury. However, the correlation between EtCO2 and venous or arterial PCO2 is uncertain. We aimed to assess the correlation between EtCO2 and PCO2 in intubated patients undergoing critical care transport (CCT), and in specific subgroups of patients.MethodsWe performed a retrospective review of patients undergoing emergency transport by a multi-state CCT agency. Patients were included if they had an advanced airway and both an EtCO2 and PCO2 reading within 5 minutes of each other. We obtained data on patient demographics, transport characteristics, medical categories, vital signs, lab values, and specific interventions. We performed univariable and multivariable binary logistic regression to assess the association between delta PCO2 and these characteristics.ResultsWe included 6,459 patients (mean age 58.4 years [SD 18.5], 57.1% male), of which a subset of 551 patients had multiple EtCO2-PCO2 measurements within 5 minutes. The median (IQR) initial delta PCO2 was 12.9 mmHg (7.1, 21.9). 3,967 (61.4%) patients had a delta PCO2 >10 mmHg and 1,843 (28.5%) had a delta PCO2 >20 mmHg. We identified an independent association between delta PCO2 >10 mmHg and age, male sex, interfacility transport, venous sampling site, respiratory rate, hypotension, hypoxia, and thoracostomy. In patients with multiple blood gas measurements, 76% had delta PCO2 >10 mmHg over the duration of the transport.ConclusionsWe identified substantial differences between EtCO2 and PCO2 across patients with medical and traumatic conditions undergoing critical care transport. The PCO2 assessment should be strongly considered as part of ventilatory management in patients encountered in emergency and critical care settings.

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