Acid–base disorders are common in emergency and critical care practice and require timely evaluation to guide management. Arterial blood gas (ABG) analysis remains the reference standard for assessing acid–base status, but obtaining ABG is invasive, painful, time-consuming, and resource-intensive. End-tidal carbon dioxide (ETCO2) monitoring with quantitative waveform capnography is a noninvasive method that reflects ventilation and, indirectly, metabolic status. The potential for ETCO2 to act as a surrogate marker for selected ABG parameters, particularly arterial bicarbonate (HCO3-), motivated the reported investigation.
The study aimed to determine the relationship between ETCO2 and arterial blood gas bicarbonate (HCO3-) levels in adult patients presenting with acid–base disorders to the emergency department and critical care unit.
This was a prospective, observational, analytical study conducted in the emergency department and critical care unit of a tertiary care teaching hospital. The work was reported as a free article in Annals of African Medicine with DOI 10.4103/aam.aam_95_26 and PubMed identifier 42757558.
A total of 100 adult patients aged 18 years and above who presented with acid–base disorders were included. The investigators recorded ETCO2 values using quantitative waveform capnography at the time of presentation. Simultaneous arterial blood gas analysis measured pH, PaCO2, PaO2, and HCO3-. The association between ETCO2 and ABG parameters was analyzed using the Pearson correlation coefficient. Mean age and gender distribution were reported for the study population.
The mean age of participants was 59.22 ± 9.30 years, and the cohort had a near-equal distribution of males and females. The principal findings reported were:
These relationships suggest that lower ETCO2 measurements were associated with more severe metabolic acidosis, whereas higher ETCO2 tended to align with higher bicarbonate and PaCO2 values.
The study supports the concept that ETCO2 can reflect underlying acid–base physiology, correlating with both arterial bicarbonate and PaCO2. In emergency and critical care settings where rapid, noninvasive assessment is valuable, ETCO2 monitoring by capnography could provide early, bedside information about metabolic derangement. This may be particularly useful for trend monitoring or early triage while awaiting confirmatory ABG results.
However, the authors explicitly state that ETCO2 cannot replace arterial blood gas analysis. ABG remains necessary for definitive measurement of pH, PaCO2, HCO3-, and oxygenation (PaO2). ETCO2 may be best used as an adjunct to guide early decision-making and to prompt rapid ABG testing when indicated.
The abstract reports core methods and principal correlations but does not include several details that would be helpful for interpreting and applying results:
If the full text contains these data, clinicians should review it for effect sizes, subgroup findings (for example ventilated vs nonventilated patients), and methodological specifics before applying results in practice.
In this cohort of 100 adults with acid–base disorders presenting to the emergency department and critical care unit, ETCO2 measured by waveform capnography correlated positively with arterial bicarbonate (HCO3-) and PaCO2, and negatively with pH. The authors conclude that ETCO2 monitoring may serve as a rapid, noninvasive adjunct for early assessment of metabolic derangements in emergency settings, but it does not replace ABG analysis. Detailed numerical correlation metrics and subgroup information were not reported in the abstract; readers should consult the full article for complete statistical results and methodology if needed.