What is the most likely diagnosis and initial management for a volume‑depleted diabetic patient with blood urea nitrogen 77 mg/dL, creatinine 1.9 mg/dL, glucose 359 mg/dL, chloride 88 mEq/L, and bicarbonate 33 mEq/L?

Hyperosmolar Hyperglycemic State (HHS) with Severe Volume Depletion

This patient most likely has hyperosmolar hyperglycemic state (HHS) rather than diabetic ketoacidosis (DKA), and requires immediate aggressive fluid resuscitation with isotonic saline at 15-20 mL/kg/hour, followed by insulin therapy only after excluding hypokalemia. 1

Diagnostic Reasoning

The laboratory values point strongly toward HHS rather than DKA:

• Elevated bicarbonate (33 mEq/L) indicates metabolic alkalosis or at minimum absence of significant acidosis, which rules out DKA (requires bicarbonate <15 mEq/L) 1, 2
• Marked hyperglycemia (359 mg/dL) with severe volume depletion evidenced by BUN:Cr ratio of 40:1 (77/1.9), far exceeding the normal 10-15:1 ratio 3
• Low chloride (88 mEq/L) suggests hypochloremic metabolic alkalosis from volume contraction and vomiting, not the anion gap acidosis of DKA 1
• Calculated effective osmolality = 2(Na) + glucose/18 ≈ 2(corrected Na) + 20, likely exceeding 320 mOsm/kg (HHS diagnostic threshold) 1

Critical Pitfall to Avoid

The elevated creatinine may be spuriously elevated due to interference from ketones in automated assays if any ketoacidosis is present, though the high bicarbonate makes significant ketoacidosis unlikely 4. The disproportionately elevated BUN:Cr ratio (>20:1) indicates severe prerenal azotemia from volume depletion, common in elderly patients with hypercatabolic states 3.

Initial Management Algorithm

Step 1: Immediate Fluid Resuscitation (First Priority)

• Begin isotonic (0.9%) saline at 15-20 mL/kg/hour for the first 1-2 hours to restore circulatory volume and tissue perfusion 1
• This addresses the typical 6-9 liter total body water deficit in HHS 2
• Correct serum sodium for hyperglycemia: add 1.6 mEq/L for every 100 mg/dL glucose above 100 mg/dL 1
• After initial resuscitation, switch to 0.45% saline at 4-14 mL/kg/hour if corrected sodium is normal or elevated 1

Step 2: Obtain Essential Laboratory Studies

Before starting insulin, obtain STAT: 1

• Serum potassium (mandatory before insulin)
• Arterial or venous blood gas (to confirm absence of acidosis)
• Complete metabolic panel
• Serum or blood β-hydroxybutyrate (preferred over urine ketones) 2, 5
• Complete blood count with differential
• Urinalysis and cultures if infection suspected
• Electrocardiogram

Step 3: Potassium Management (Critical Before Insulin)

Do NOT start insulin if serum potassium <3.3 mEq/L - this can cause fatal cardiac arrhythmias 2, 6. Instead:

• Aggressively replace potassium first until K+ >3.3 mEq/L 2
• Once K+ is 3.3-5.5 mEq/L and adequate urine output confirmed, add 20-30 mEq/L potassium to IV fluids (2/3 KCl and 1/3 KPO4) 1
• If K+ >5.5 mEq/L, hold potassium replacement but recheck frequently as insulin will drive it intracellularly 7

Step 4: Insulin Therapy (Only After Excluding Hypokalemia)

Once K+ >3.3 mEq/L: 1, 6

• Start continuous IV regular insulin infusion at 0.1 units/kg/hour (typically 5-7 units/hour in adults)
• No initial bolus is recommended for HHS (unlike DKA) 1
• Target glucose decline of 50-75 mg/dL per hour 1
• If glucose doesn't fall by 50 mg/dL in first hour, double insulin infusion hourly until steady decline achieved 1, 2

Step 5: Transition to Dextrose-Containing Fluids

• When glucose reaches 250-300 mg/dL, add 5% dextrose to IV fluids while continuing insulin infusion 1
• This prevents hypoglycemia while allowing continued treatment of any residual ketosis 5
• Continue insulin at 0.05-0.1 units/kg/hour with dextrose 2

Monitoring Protocol

• Check glucose, electrolytes, BUN, creatinine every 2-4 hours during active treatment 1, 2
• Monitor for fluid overload, especially with cardiac or renal compromise 1
• Watch for mental status changes suggesting cerebral edema (rare but serious complication) 2
• Venous pH and anion gap can be followed without repeated arterial blood gases 1, 2

Resolution Criteria for HHS

Treatment is complete when: 2, 5

• Glucose <200 mg/dL
• Mental status normalized
• Serum osmolality <315 mOsm/kg
• Patient able to tolerate oral intake

Common Pitfalls to Avoid

• Never start insulin before checking potassium - insulin-induced hypokalemia can cause respiratory paralysis and fatal arrhythmias 6
• Don't stop IV insulin when glucose normalizes - continue until mental status and osmolality normalize 2
• Avoid overly aggressive fluid resuscitation (>50 mL/kg over first 4 hours) which can cause cerebral edema 1, 2
• Don't use bicarbonate therapy - it provides no benefit and the elevated bicarbonate here suggests alkalosis, not acidosis 2

1, 2, 5, 6, 8, 7, 4, 3