What is the most likely diagnosis in a patient with arterial blood gas pH 7.00, pCO2 54 mm Hg, bicarbonate 12 mmol/L, random blood glucose >350 mg/dL, low Glasgow Coma Scale, and normal magnetic resonance imaging and computed tomography?

Diagnosis: Severe Diabetic Ketoacidosis (DKA)

This patient has severe diabetic ketoacidosis with mixed acid-base disorder (metabolic acidosis with respiratory acidosis), requiring immediate intensive care management with IV insulin, aggressive fluid resuscitation, and close monitoring for cerebral edema.

Diagnostic Reasoning

Confirming Severe DKA

The patient meets all diagnostic criteria for severe DKA based on the American Diabetes Association classification 1:

• pH 7.00 (severe DKA defined as pH <7.00) 1
• Bicarbonate 12 mEq/L (severe DKA defined as bicarbonate <10 mEq/L; this patient is at the moderate-severe boundary) 1
• Blood glucose >350 mg/dL (diagnostic threshold is >250 mg/dL) 2, 1
• Altered mental status (poor GCS) is consistent with severe DKA 1, 3

Understanding the Mixed Acid-Base Disorder

This patient has a combined metabolic and respiratory acidosis 2:

• Metabolic acidosis: Low bicarbonate (12 mEq/L) with low pH indicates primary metabolic acidosis from ketoacid accumulation 2
• Respiratory acidosis: Elevated pCO2 (54 mm Hg; normal 34-46 mm Hg) indicates inadequate respiratory compensation 2
• Expected compensation: In pure metabolic acidosis, the patient should hyperventilate (Kussmaul respirations) to lower pCO2 and partially compensate 4. The elevated pCO2 suggests respiratory failure or respiratory muscle fatigue from severe acidosis 2

Why Neuroimaging is Normal

Normal CT and MRI do not exclude DKA as the cause of altered consciousness 1. The decreased GCS is explained by:

• Severe acidosis (pH 7.00) directly depresses central nervous system function 2, 1
• Hyperosmolality from hyperglycemia (effective osmolality = 2[Na] + glucose/18) 2
• Cerebral edema risk during treatment, which is why imaging was appropriately obtained 2, 1

Calculating Anion Gap

To confirm high anion gap metabolic acidosis characteristic of DKA 1:

Anion Gap = [Na+] - ([Cl-] + [HCO3-]) 1

Without provided sodium and chloride values, we infer an elevated anion gap based on the clinical presentation. The anion gap should be >10-12 mEq/L in DKA 1.

Immediate Management Protocol

1. Airway and Respiratory Support

Consider intubation immediately given 2:

• Glasgow Coma Scale <8 is an indication for invasive mechanical ventilation 2
• pH <7.15 with respiratory acidosis (pCO2 54 mm Hg) indicates impending respiratory arrest 2
• Severe respiratory distress or inability to protect airway 2

2. Fluid Resuscitation

Begin aggressive isotonic saline (0.9% NaCl) at 15-20 mL/kg/hour for the first hour 2, 1:

• Total body water deficit in DKA is typically 6-9 liters 1
• Replace estimated deficits within 24 hours 2
• Monitor closely for fluid overload and cerebral edema, especially with altered mental status 2, 1

3. Insulin Therapy

Start continuous IV regular insulin at 0.1 units/kg/hour WITHOUT initial bolus once potassium ≥3.3 mEq/L 1:

• Do NOT give subcutaneous insulin in a patient with altered consciousness 1
• If glucose does not fall by 50 mg/dL in the first hour, double the insulin rate hourly until steady decline of 50-75 mg/dL per hour 1
• When glucose reaches 200-250 mg/dL, add 5-10% dextrose to IV fluids while continuing insulin to clear ketones 2, 1

4. Potassium Management

Check serum potassium BEFORE starting insulin 1:

• If K+ <3.3 mEq/L: Delay insulin and give aggressive potassium replacement to prevent fatal arrhythmias 1
• If K+ 3.3-5.5 mEq/L: Add 20-30 mEq/L potassium to IV fluids (2/3 KCl, 1/3 KPO4) 2, 1
• If K+ >5.5 mEq/L: Hold potassium and recheck frequently 1

5. Monitoring Protocol

Check every 2-4 hours 1:

• Venous pH and bicarbonate (arterial blood gases not needed after initial diagnosis) 1
• Glucose, electrolytes (Na, K, Cl), BUN, creatinine 1
• Anion gap to monitor acidosis resolution 1
• Beta-hydroxybutyrate (preferred over urine ketones) 1

6. Bicarbonate Therapy

Do NOT give bicarbonate unless pH <6.9 1:

• Bicarbonate provides no benefit in DKA resolution 1
• This patient's pH of 7.00 does not meet the threshold for bicarbonate administration 1

Critical Pitfalls to Avoid

• Never stop IV insulin when glucose normalizes – ketoacidosis takes longer to resolve than hyperglycemia 1
• Never use subcutaneous insulin in critically ill or unconscious patients 1
• Never restrict fluids – aggressive hydration is essential 2, 1
• Never give normal saline for rehydration if this were diabetes insipidus (but this is clearly DKA) 5
• Monitor closely for cerebral edema during treatment, especially with rapid fluid administration 2, 1

Resolution Criteria

DKA is resolved when ALL of the following are met 1:

• Glucose <200 mg/dL 1
• Venous pH >7.3 1
• Serum bicarbonate ≥18 mEq/L 1
• Anion gap ≤12 mEq/L 1

Transition to Subcutaneous Insulin

Administer basal subcutaneous insulin 2-4 hours BEFORE stopping IV insulin to prevent rebound hyperglycemia and recurrent ketoacidosis 1.