Relationship between End-tidal Carbon Dioxide and Arterial Blood Gas Bicarbonate Levels in Patients with Acid–base Disorders Presenting to the Emergency Department and Critical Care Unit

BACKGROUND: Acid-base disorders are frequently encountered in the emergency department and critical care unit and require prompt assessment for timely management. Arterial blood gas analysis remains the gold standard for evaluating acid-base status; however, it is invasive, painful, time-consuming, and costly. End-tidal carbon dioxide (ETCO2) monitoring using capnography is a noninvasive technique that reflects ventilation and metabolic status and may serve as a surrogate marker for certain arterial blood gas parameters. AIM: To determine the relationship between ETCO2 and arterial blood gas bicarbonate (HCO3-) levels in patients presenting with acid-base disorders. STUDY DESIGN AND SETTING: This prospective, observational, and analytical study was conducted in the emergency department and critical care unit of a tertiary care teaching hospital. SUBJECTS AND METHODS: A total of 100 adult patients aged 18 years and above presenting with acid-base disorders were included. ETCO2 values were recorded using quantitative waveform capnography and arterial blood gas analysis was performed simultaneously to measure pH, PaCO2, PaO2, and HCO3- levels. Correlation between ETCO2 and arterial blood gas parameters was analyzed using Pearson correlation coefficient. RESULTS: The mean age of the study population was 59.22 ± 9.30 years, with a near-equal gender distribution. ETCO2 showed a statistically significant positive correlation with arterial bicarbonate and PaCO2 levels, and a significant negative correlation with pH. These findings indicate that lower ETCO2 values were associated with more severe metabolic acidosis. CONCLUSION: ETCO2 monitoring demonstrates a significant correlation with arterial bicarbonate and PaCO2 levels in patients with acid-base disorders. While ETCO2 cannot replace arterial blood gas analysis, it may serve as a rapid, noninvasive adjunct for the early assessment of metabolic derangements in emergency settings.