End-tidal carbon dioxide underestimates plasma carbon dioxide during emergent trauma laparotomy leading to hypoventilation and misguided resuscitation: A western trauma association multicenter study

BACKGROUND: End-tidal carbon dioxide (ETCO₂) is routinely used during elective surgery to monitor ventilation. The role of ETCO₂ monitoring in emergent trauma operations is poorly understood. We hypothesized that ETCO₂ values underestimate plasma carbon dioxide (pCO₂) values during resuscitation for hemorrhagic shock. METHODS: Multicenter trial was performed analyzing the correlation between ETCO₂ and pCO₂ levels. RESULTS: Two hundred fifty-six patients resulted in 587 matched pairs of ETCO₂ and pCO₂. Correlation between these two values was very poor with an R² of 0.04. 40.2% of patients presented to the operating room acidotic and hypercarbic with a pH less than 7.30 and a pCO₂ greater than 45 mm Hg. Correlation was worse in patients that were either acidotic or hypercarbic. Forty-five percent of patients have a difference greater than 10 mm Hg between ETCO₂ and pCO₂. A pH less than 7.30 was predictive of an ETCO₂ to pCO₂ difference greater than 10 mm Hg. A difference greater than 10 mm Hg was predictive of mortality independent of confounders. CONCLUSION: Nearly one half (45%) of patients were found to have an ETCO₂ level greater than 10 mm Hg discordant from their PCO₂ level. Reliance on the discordant values may have contributed to the 40% of patients in the operating room that were both acidotic and hypercarbic. Early blood gas analysis is warranted, and a lower early goal of ETCO₂ should be considered. LEVEL OF EVIDENCE: Therapeutic, level IV.