What is the dose of regular insulin according to a sliding scale regimen and what other management is required to prevent Diabetic Ketoacidosis (DKA) in a patient with Hyperglycemia?

Management of Hyperglycemia (RBS 420 mg/dL) to Prevent DKA

Do NOT use sliding scale insulin alone to prevent DKA—this patient needs immediate assessment for existing DKA, aggressive IV fluid resuscitation, continuous IV insulin infusion at 0.1 units/kg/hour if DKA is present, and transition to basal-bolus subcutaneous insulin once metabolically stable. 1

Immediate Assessment Required

Before any insulin dosing, you must determine if this patient already has DKA or is at risk:

• Check diagnostic criteria immediately: arterial pH, serum bicarbonate, serum/urine ketones, anion gap, and electrolytes (especially potassium) 1
• DKA is defined as: glucose >250 mg/dL, pH <7.3, bicarbonate <15 mEq/L, and presence of ketonemia/ketonuria 1
• Identify precipitating factors: infection, MI, stroke, pancreatitis, insulin omission, or SGLT2 inhibitor use 1

Critical Potassium Check BEFORE Any Insulin

• If K+ <3.3 mEq/L: DO NOT START INSULIN—aggressively replace potassium first to prevent fatal arrhythmias and respiratory muscle weakness 1
• If K+ 3.3-5.5 mEq/L: Add 20-30 mEq potassium per liter IV fluid once urine output confirmed 1
• Target serum K+ 4-5 mEq/L throughout treatment 1

If DKA is Present: IV Insulin Protocol (NOT Sliding Scale)

Sliding scale insulin is contraindicated and leads to worse outcomes in DKA management 2

Initial IV Insulin Dosing:

• Give IV bolus: 0.15 units/kg regular insulin (only after confirming K+ ≥3.3 mEq/L) 3
• Start continuous IV infusion: 0.1 units/kg/hour regular insulin 1, 3
• For a 70 kg patient: This equals approximately 10.5 units bolus, then 7 units/hour infusion 3

Fluid Resuscitation (Equally Critical):

• Start with isotonic saline (0.9% NaCl): 15-20 mL/kg/hour (approximately 1-1.5 L) in first hour 1, 3
• When glucose reaches 250 mg/dL: Switch to 5% dextrose with 0.45-0.75% NaCl while continuing insulin to prevent hypoglycemia and ensure complete ketoacidosis resolution 1, 3

Monitoring and Adjustment:

• Check glucose every 1-2 hours: Expect 50-75 mg/dL decline per hour 1, 2
• If glucose doesn't fall by 50 mg/dL in first hour: Check hydration; if adequate, double insulin infusion rate hourly until steady decline achieved 1
• Continue IV insulin until DKA resolves: pH >7.3, bicarbonate ≥18 mEq/L, anion gap ≤12 mEq/L, glucose <200 mg/dL 1, 3

If DKA is NOT Present: Subcutaneous Insulin Initiation

For hyperglycemia without DKA (which must be confirmed by labs):

• Start basal insulin: 0.5 units/kg/day of long-acting insulin (glargine or detemir) given once daily 2
• For a 70 kg patient: This equals approximately 35 units once daily 2
• Add prandial insulin: Rapid-acting insulin before meals using 1:10 carbohydrate ratio 2
• Correction dose formula: (Current glucose - Target glucose) ÷ 50, where 1 unit lowers glucose by 50 mg/dL 2

Transition from IV to Subcutaneous Insulin (After DKA Resolution)

This is where most errors occur—premature discontinuation of IV insulin causes rebound hyperglycemia and recurrent DKA 1, 4

Critical Timing:

• Administer first dose of basal insulin 2-4 hours BEFORE stopping IV insulin 1, 2, 3
• Never stop IV insulin before giving subcutaneous basal insulin 2

Dosing Calculation:

• Method 1: Calculate total daily dose = Average hourly IV insulin rate (from last 12 hours) × 24 hours 2
• Give 50% as basal insulin (glargine/detemir once daily) and 50% as prandial insulin (rapid-acting before meals, divided equally) 2
• Method 2: Use 0.5-0.65 units/kg/day total, with 50% basal and 50% prandial 2

Why Sliding Scale Alone is Dangerous

• Sliding scale (correction-only) insulin without basal coverage leads to worse outcomes and higher complication rates 2
• It is reactive rather than proactive, allowing hyperglycemia to persist and potentially progress to DKA 2
• Always use basal-bolus regimen with scheduled basal insulin plus prandial and correction doses 2

Additional Critical Management

• Discontinue SGLT2 inhibitors immediately if patient is taking them—they should have been stopped 3-4 days before any acute illness 1, 2
• Hold metformin during acute illness and restart once stable 2
• Treat underlying precipitating cause: Start antibiotics if infection suspected 1
• Monitor electrolytes every 2-4 hours during active treatment 1
• Bicarbonate is NOT recommended for pH >6.9-7.0, as it may worsen outcomes 1

Common Pitfalls to Avoid

• Never use sliding scale insulin alone—this is the most common error and increases DKA risk 2
• Never stop IV insulin when glucose normalizes—continue until ketoacidosis resolves (pH, bicarbonate, anion gap normalized) 1
• Never forget the 2-4 hour overlap between starting subcutaneous basal insulin and stopping IV insulin 1, 2, 3
• Never start insulin if K+ <3.3 mEq/L—correct potassium first 1
• Never forget to add dextrose to IV fluids when glucose reaches 250 mg/dL while continuing insulin 1, 3