How to administer insulin to a 13-year-old, 40 kg patient with diabetic ketoacidosis (DKA) and altered mental status?

Insulin Administration in Pediatric DKA with Altered Mental Status

Immediate Insulin Protocol

For a 13-year-old, 40 kg patient with DKA and altered mental status, administer continuous intravenous regular insulin at 0.1 units/kg/hour (4 units/hour) after confirming serum potassium ≥3.3 mEq/L, preceded by an optional IV bolus of 0.1 units/kg (4 units). 1, 2

Critical Pre-Insulin Checklist

Before starting any insulin therapy, you must:

• Check serum potassium immediately - if K+ <3.3 mEq/L, do NOT start insulin under any circumstances, as this can cause fatal cardiac arrhythmias 1, 2
• If K+ <3.3 mEq/L, aggressively replace potassium with 20-40 mEq/L in IV fluids until levels reach ≥3.3 mEq/L 1
• Obtain ECG to assess for cardiac effects of hypokalemia 1
• Confirm adequate urine output before potassium repletion 3

Step-by-Step Insulin Administration

Initial Dosing:

• Give IV bolus of regular insulin 0.1 units/kg = 4 units (optional but recommended for moderate-severe DKA) 1, 2
• Immediately start continuous IV infusion at 0.1 units/kg/hour = 4 units/hour 1, 2, 4
• Use only regular insulin (not rapid-acting analogs) for IV infusion in critically ill patients with altered mental status 2

Target glucose decline: 50-75 mg/dL per hour 1, 2

Adjusting the Insulin Infusion

• If glucose does not fall by 50 mg/dL in the first hour: verify adequate hydration status, then double the insulin infusion rate every hour until achieving steady decline of 50-75 mg/dL/hour 1, 2
• When glucose reaches 250 mg/dL: reduce insulin to 0.05-0.1 units/kg/hour (2-4 units/hour) AND switch IV fluid to 5% dextrose with 0.45-0.75% saline 1, 2
• Continue insulin infusion until complete DKA resolution, regardless of glucose levels 2

Concurrent Fluid and Electrolyte Management

Fluid Resuscitation

• Begin with isotonic saline (0.9% NaCl) at 15-20 mL/kg/hour = 600-800 mL/hour for first hour 1, 2
• Total fluid replacement should approximate 1.5 times 24-hour maintenance requirements 1

Potassium Management Throughout Treatment

This is where most errors occur:

• If K+ 3.3-5.5 mEq/L: add 20-30 mEq/L potassium to each liter of IV fluid (use 2/3 KCl and 1/3 KPO₄) once urine output confirmed 1, 2
• If K+ >5.5 mEq/L: withhold potassium initially but monitor closely every 2 hours, as insulin will drive it intracellularly rapidly 2
• Target serum potassium: 4-5 mEq/L throughout treatment 2, 3
• Total body potassium depletion averages 3-5 mEq/kg (120-200 mEq for this patient), and insulin therapy will unmask this depletion 3

Monitoring Requirements

• Blood glucose: every 1-2 hours initially, then every 2-4 hours 1, 3
• Serum electrolytes, pH, bicarbonate, anion gap: every 2-4 hours 1, 2
• Potassium: every 2 hours during active treatment due to rapid shifts 3
• Neurological status: continuously monitor for signs of cerebral edema (headache, altered mental status worsening, neurological deterioration) - this is more common in children and adolescents 3

DKA Resolution Criteria

DKA is resolved when ALL of the following are met 1, 2:

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

Transition to Subcutaneous Insulin

This is the most common error leading to DKA recurrence:

• Administer basal insulin (glargine or detemir) subcutaneously 2-4 hours BEFORE stopping IV insulin - this overlap is absolutely critical 1, 2, 3
• For a 40 kg patient, start basal insulin at 0.5 units/kg/day = 20 units once daily (50% of total daily dose as basal) 3
• Continue IV insulin for 1-2 hours after giving subcutaneous insulin 1
• Never stop IV insulin without prior basal insulin administration 1, 3

Calculating Subcutaneous Doses

• Total daily dose: Average hourly IV insulin rate from last 12 hours × 24 hours 3
• Basal insulin: 50% of total daily dose given as long-acting insulin once daily 3
• Prandial insulin: 50% of total daily dose divided equally before three meals as rapid-acting insulin 3

Critical Pitfalls to Avoid

• Never start insulin if K+ <3.3 mEq/L - this causes fatal arrhythmias 1, 2
• Never stop IV insulin before giving subcutaneous basal insulin - causes rebound hyperglycemia and recurrent DKA 1, 2, 3
• Never interrupt insulin infusion when glucose falls - add dextrose to IV fluids instead and reduce insulin rate 2
• Never use subcutaneous insulin in critically ill patients with altered mental status - IV insulin is the standard of care for this population 2
• Never use correction-only (sliding scale) insulin without basal coverage - leads to worse outcomes 3

Special Considerations for Altered Mental Status

• Continuous IV insulin at 0.1 units/kg/hour is the absolute standard of care for critically ill and mentally obtunded patients 2
• Subcutaneous rapid-acting insulin analogs are only appropriate for hemodynamically stable, alert patients with mild-moderate DKA 1, 2, 5
• Monitor closely for cerebral edema, which occurs more commonly in children and adolescents than adults 3