Utility of Initial Prehospital End-tidal Carbon Dioxide Measurements to Predict Poor Outcomes in Adult Asthmatic Patients

Abstract

Study objective. To determine if an initial (before treatment) prehospital end-tidal carbon dioxide (EtCO₂) measurement in adult, non-chronic obstructive pulmonary disease (COPD), asthmatic patients predicts patient outcomes. Methods. This is a retrospective chart review of EtCO₂ assessment data in a convenience sample of adult, asthmatic patients transported via advanced life support (ALS) units to a large, urban, academic hospital. Initial EtCO₂ measurements were obtained routinely on all respiratory distress patients in the field, and emergency department physicians were unaware of the results. Data were analyzed using descriptive statistics, including percentages, means, and 95% confidence intervals (CI). Results. We reviewed data for prehospital initial EtCO₂ measurements on 299 unique asthma patients (repeat visits by same patient were not included). Mean (SD) age was 43.1 years (12.5) and 142 (47.5%) were male. The mean EtCO₂ measurement was 38.8 mmHg (SD ± 9.5; CI: 37.7–39.9; range: 14–82). Examination of initial EtCO₂ measurements by deciles revealed that extreme values, in the lowest (14–28 mmHg) and highest (50–82 mmHg) deciles, experienced more markers of poor outcome than less extreme measurements. Patients were thus dichotomized by extreme (n = 59) or nonextreme (n = 240) EtCO₂ measurements. More extreme patients were ultimately intubated (30.5 vs. 5.8%; p < 0.001; positive predictive value (ppv) = 30.5% ), and/or admitted to the intensive care unit (ICU) (28.8 vs. 6.7%; p <0.001; ppv = 28.8%), and/or died (5.1 vs. 0%; p = 0.007 [Fisher's exact test]; ppv = 5.1%), than nonextreme patients, respectively. Conclusion. Extreme (both low and high) prehospital initial EtCO₂ measurements may be associated with markers of poor patient outcomes. Future work will prospectively determine whether the addition of this information improves early recognition of severe asthma episodes beyond clinical assessment.

Key words: :

• emergency medicine
• asthma
• end-tidal carbon dioxide
• EtCO₂