Prehospital CO2 Levels Predict Trauma Mortality Transfusion Needs

While battlefield medics have long relied on experience and intuition to assess casualties, modern emergency medicine increasingly demands precise metrics to guide critical decisions. In trauma care, rapid prehospital evaluation is paramount. Traditional vital signs like blood pressure and shock index (SI) remain widely used, but their predictive limitations have sparked interest in more accurate biomarkers. A new prospective, observational, multicenter study reveals that prehospital end-tidal carbon dioxide (ETCO ₂ ) monitoring—particularly via nasal cannula continuous (NCC) measurement—shows remarkable superiority in predicting mortality and massive transfusion needs among trauma patients.

This investigation sought to evaluate ETCO ₂ 's prognostic value in prehospital trauma care. Prior studies suggested ETCO ₂ 's potential for identifying hemorrhagic shock and in-hospital mortality, but evidence remained scarce regarding its prehospital application across different monitoring methods (NCC versus intubated ventilation). Conducted across two Level I trauma centers in Denver, Colorado, this study aimed to establish ETCO ₂ as a reliable predictor while comparing its performance against conventional vital signs.

From February 2021 through June 2022, researchers analyzed 550 trauma patients transported by Denver Health EMS with at least one prehospital ETCO ₂ reading. Patients underwent either:

• Nasal Cannula Continuous Monitoring (NCC): A noninvasive method providing real-time CO ₂ measurements via specialized nasal cannulae, ideal for non-intubated patients.
• Intubated Ventilation Monitoring (ILVC): Standard CO ₂ detection through ventilator circuits for mechanically ventilated patients.

Data collection included demographics, injury patterns, physiological markers (ETCO ₂ , systolic pressure, shock index), and clinical outcomes (mortality, transfusion requirements). Statistical analyses employed multivariable logistic regression to control for confounders.

The cohort demonstrated a 10.4% mortality rate and 6.6% massive transfusion rate. Critical insights emerged:

• Mortality Prediction: Lower prehospital ETCO ₂ values strongly correlated with higher mortality risk. ETCO ₂ remained an independent predictor even after adjusting for age, injury severity, and physiological parameters.
• Transfusion Needs: Depressed ETCO ₂ levels effectively identified patients requiring massive transfusions, enabling earlier intervention.
• Superior Predictive Power: ETCO ₂ outperformed traditional metrics like systolic pressure and shock index in both outcome predictions.

ETCO ₂ 's physiological basis—reflecting ventilation, perfusion, and metabolic status—explains its predictive strength. In hemorrhagic shock, ETCO ₂ declines due to compensatory hyperventilation and reduced tissue CO ₂ production from hypoperfusion. This makes it an early warning system for circulatory collapse.

The study advocates for broader prehospital ETCO ₂ adoption to:

• Enhance triage accuracy for high-risk patients
• Facilitate timely blood product mobilization
• Improve shock recognition during transport

While the multicenter design strengthens validity, findings may not generalize to all trauma settings. Unrecorded prehospital interventions (e.g., fluid resuscitation) could influence ETCO ₂ readings. Future research should explore ETCO ₂ -guided resuscitation protocols and subtype-specific applications.

This research establishes prehospital ETCO ₂ monitoring—whether via NCC or ILVC—as a transformative tool for trauma care, offering clinicians a more precise compass in life-or-death decisions.