Why CO2 Monitoring Matters in Euglycemic DKA
Monitoring CO2 levels in euglycemic DKA is critical because bicarbonate and CO2 are your primary indicators of acidosis severity and treatment response when glucose cannot serve as a reliable marker—and in euglycemic DKA, glucose levels remain deceptively normal (<250 mg/dL) despite ongoing life-threatening ketoacidosis. 1, 2
The Core Problem: Glucose Misleads You
In classic DKA, you track three parameters simultaneously: glucose, pH/bicarbonate, and ketones. In euglycemic DKA, glucose fails as a severity marker because it stays below 250 mg/dL throughout the crisis. 1, 2 This leaves you dependent on acid-base parameters—specifically CO2 (or bicarbonate, which directly correlates)—to determine:
- Whether DKA exists at all: Serum bicarbonate must be <15 mEq/L (corresponding to low CO2) to meet diagnostic criteria, even when glucose is normal 1, 2
- How severe the DKA is: CO2/bicarbonate stratifies severity (mild: bicarbonate 15-18 mEq/L; moderate: 10-15 mEq/L; severe: <10 mEq/L) 1, 2
- Whether treatment is working: Resolution requires bicarbonate ≥18 mEq/L and venous pH >7.3, not glucose normalization 1, 3
Why Euglycemic DKA Happens and Why It's Dangerous
Euglycemic DKA occurs increasingly with SGLT2 inhibitors (which cause urinary glucose loss), ketogenic diets, pregnancy, reduced caloric intake, or insulin pump failure with some residual insulin effect. 4, 2 The danger is that clinicians may dismiss the diagnosis when they see "normal" glucose, delaying recognition of severe acidosis. 2
The Monitoring Algorithm for Euglycemic DKA
Initial Assessment
- Check venous pH, serum bicarbonate (or CO2), and blood β-hydroxybutyrate immediately alongside glucose 1, 2
- Calculate anion gap: [Na⁺] - ([Cl⁻] + [HCO₃⁻]); should be >10-12 mEq/L in DKA 1, 2
- Diagnose euglycemic DKA when: glucose <250 mg/dL BUT pH <7.3, bicarbonate <15 mEq/L, and elevated β-hydroxybutyrate 1, 2
During Treatment
- Monitor CO2/bicarbonate every 2-4 hours along with electrolytes, pH, and β-hydroxybutyrate 1, 3
- Start dextrose 5% immediately with 0.9% saline when beginning insulin treatment in euglycemic DKA (unlike classic DKA where you wait until glucose falls to 250 mg/dL) 3
- Continue insulin infusion until bicarbonate ≥18 mEq/L and pH >7.3, regardless of glucose levels 3
Resolution Criteria
DKA is resolved only when ALL of the following are met: glucose <200 mg/dL, bicarbonate ≥18 mEq/L, venous pH >7.3, and anion gap ≤12 mEq/L. 1, 3 In euglycemic DKA, the glucose criterion is already met, making CO2/bicarbonate your sole metabolic endpoint.
Critical Pitfalls to Avoid
Never stop insulin when glucose normalizes in euglycemic DKA—ketoacidosis takes longer to clear than hyperglycemia, and premature insulin cessation causes recurrent ketoacidosis. 4, 3 The bicarbonate/CO2 must normalize first. 3
Don't rely on urine ketones—they measure acetoacetate, not β-hydroxybutyrate (the predominant ketoacid), and paradoxically worsen as treatment succeeds. 1, 3 Use blood β-hydroxybutyrate instead. 1, 2
Venous pH suffices after initial diagnosis—avoid repeated arterial sticks, as venous pH tracks acidosis resolution adequately (typically 0.03 units lower than arterial). 1, 3
Why CO2 Correlates with Clinical Severity
CO2 levels reflect respiratory compensation for metabolic acidosis. 5, 6 Low CO2 (<18 mmol/L on basic metabolic panel) indicates the body is hyperventilating to blow off CO2 and partially compensate for the acidosis. 7, 6 End-tidal CO2 monitoring shows strong correlation with arterial CO2 and bicarbonate (ETCO2 >24.5 mmHg rules out DKA with 90% sensitivity/specificity), making it a useful noninvasive adjunct. 8, 6 In severe DKA, profound hypocapnia from compensatory hyperventilation can complicate mechanical ventilation if needed. 9
The Bottom Line for Euglycemic DKA
In euglycemic DKA, CO2/bicarbonate becomes your primary treatment target because glucose cannot guide you. 1, 2, 3 You must add dextrose from the start, continue insulin until acid-base parameters normalize (not glucose), and monitor CO2/bicarbonate every 2-4 hours to track resolution. 3 Missing this distinction leads to premature insulin discontinuation and recurrent ketoacidosis. 4, 3