The utility of transcutaneous carbon dioxide measurements in the emergency department: A prospective cohort study

BACKGROUND: Rapid identification of patients with occult injury and illness in the emergency department can be difficult. Transcutaneous carbon dioxide (TCO(2)) and oxygen (TO(2)) measurements may be non‐invasive surrogate markers for the identification of such patients. OBJECTIVES: To determine if TCO(2) or TO(2) are useful adjuncts for identifying severe illness and the correlation between TCO(2), lactate, and end tidal carbon dioxide (ETCO(2)). METHODS: Prospective TCO(2) and TO(2) measurements at a tertiary level 1 trauma center were obtained using a transcutaneous sensor on 300 adult patients. Severe illness was defined as death, intensive care unit (ICU) admission, bilevel positive airway pressure, vasopressor use, or length of stay >2 days. TCO(2) and TO(2) were compared to illness severity using t tests and correlation coefficients. RESULTS: Mean TO(2) did not differ between severe illness (58.9, 95% CI 54.9–62.9) and non‐severe illness (58.0, 95% CI 54.7–61.1). Mean TCO(2) was similar between severe (34.6, 95% CI 33–36.2) vs non‐severe illness (35.9, 95% CI 34.7–37.1). TCO(2) was 28.7 (95% CI 24.0–33.4) for ICU vs. 35.9 (95% CI 34.9–36.9) for non‐ICU patients. The mean TCO(2) in those with lactate > 2.0 was 29.8 (95% CI 25.8–33.8) compared with 35.7 (95% CI 34.9–36.9) for lactate < 2.0. TCO(2) was not correlated with ETCO(2) (r = 0.32, 95% CI 0.22–0.42). CONCLUSION: TCO(2) could be a useful adjunct for identifying significant injury and illness and patient outcomes in an emergency department (ED) population. TO(2) did not predict severe illness. TCO(2) and ETCO(2) are only moderately correlated, indicating that they are not equivalent and may be useful under different circumstances.