Background/Aim. Acute carbon monoxide poisoning (ACOP) is a medical emergency, which causes a lack of oxygen in the tissues. The aim of the study was to determine the clinical characteristics of different acid-base disorder phenotypes in ACOP patients, focusing on the association between pure high anion gap (AG) metabolic acidosis and adverse outcomes (AOs). Methods. This retrospective study included 124 ACOP patients classified into three phenotypes according to the acid-base analysis: Type 1 (pure high AG metabolic acidosis), Type 2 (mixed acid-base disorders), and Type 3 (other conditions). Clinical indicators and outcomes were compared across groups. Multivariable logistic regression identified independent risk factors for AOs. Results. Type 1 phenotype patients [22 (17.74%)] exhibited significantly lower acid-base balance parameters (pH, HCO₃⁻, standard base excess) and higher metabolic stress markers (AG, lactate; all p < 0.05). They had higher rates of systemic inflammatory response syndrome (SIRS) (72.73% vs. 46.67% and 38.60%) and intensive care unit admission (45.45% vs. 17.78% and 19.30%) than the Type 2 and 3 groups (all p < 0.05). Multivariable analysis confirmed the Type 1 phenotype as an independent risk factor for both SIRS [odds ratio (OR): 6.36, 95% confidence interval (CI): 1.486–27.213] and intensive care unit admission (OR: 4.71, 95% CI: 1.102–20.151). Conclusion. This preliminary study identifies pure high AG metabolic acidosis as a strong predictor of AOs in ACOP. This readily available arterial blood gas parameter provides a novel perspective for early risk stratification in emergency settings, though its clinical utility requires validation in prospective studies.