Adjusting Insulin Infusion in a Hyperglycemic Patient

1. When to Start an Insulin Infusion

• Initiate IV insulin when blood glucose (BG) is ≥180 mg/dL (10 mmol/L) on two occasions within 24 hours
• A continuous IV insulin infusion (CII) is preferred over intermittent SC insulin for critically ill patients - it is more flexible and titratable given the short half-life of IV insulin (~5-10 min)

2. Preparation of the Infusion

• Add 50 units of regular insulin to 50 mL normal saline → concentration of 1 unit/mL
• Flush the IV tubing with ~30 mL of solution to saturate the binding sites before connecting to the patient

3. Initial Infusion Rate

Initial rate (units/h) = Current BG (mg/dL) ÷ 100 (round to nearest whole number or 0.5)

4. Glucose Monitoring Frequency

• Every hour while on IV insulin during unstable periods (2024 SCCM recommendation: no less frequent than every 60 minutes)
• Can extend to every 2 hours once BG is stable within target range
• As frequent as every 15 minutes if hypoglycemia is impending

5. Target Blood Glucose Range

6. Step-by-Step Rate Adjustment Algorithm

If BG is NOT falling adequately (< 50 mg/dL drop or < 10% in first 2 hours):

• Increase the infusion rate by 0.5-1 unit/h

If BG is falling too fast (> 100 mg/dL/h or > 20% in first hour):

• Decrease the rate by 0.5-1 unit/h
• Avoid correcting faster than 100 mg/dL/h to prevent osmotic encephalopathy/cerebral edema

BG is in target range (140-180 mg/dL):

• Continue at the current rate
• Monitor hourly; extend to q2h once stable x2 readings

BG falls to < 100 mg/dL (hypoglycemia):

1. Stop the insulin infusion immediately
2. Start 5% dextrose at 75-100 mL/h
3. Recheck BG after 60 minutes
4. Restart infusion at a lower rate once BG >100-150 mg/dL

BG > 300-400 mg/dL despite increasing infusion:

• Consider an IV bolus of 0.05-0.1 units/kg regular insulin
• Re-evaluate for causes of insulin resistance (infection, steroids, TPN, etc.)

7. Special Situations

DKA Protocol

• Start infusion at 0.1 units/kg/h (no bolus if K+ <3.5 mEq/L - correct potassium first)
• Goal: BG decrease of 50-75 mg/dL/h
• When BG reaches < 250 mg/dL: add dextrose-containing fluid (two-bag approach), reduce insulin to 0.05 units/kg/h - do NOT stop insulin until anion gap closes (HCO3 >15 mEq/L)
• (Washington Manual of Medical Therapeutics)

Patients on Parenteral Nutrition (TPN)

• Add regular insulin directly to the TPN bag (start with ~0.1 units per gram of dextrose)
• Adjust bag-to-bag based on daily BG pattern
• Continue a separate correction-dose infusion if glucose remains uncontrolled

Perioperative / Post-op

• Maintain BG < 180 mg/dL intraoperatively with IV boluses (1 unit regular insulin IV ≈ decreases BG by ~25-30 mg/dL)
• (Morgan & Mikhail's Clinical Anesthesiology)

8. Transitioning Off IV Insulin to Subcutaneous

1. Calculate the total IV insulin used in the last 24 hours
2. Convert to subcutaneous: give 80% of total daily dose as basal/bolus SC
3. Administer the first SC basal insulin dose 2 hours BEFORE stopping the IV infusion (to prevent rebound hyperglycemia - Washington Manual)
4. Continue monitoring BG every 4-6 hours after transition

Key Principles to Remember

• Three factors that make a protocol effective: (1) adjust based on current AND previous BG, (2) consider the rate of change (trending up vs down), (3) frequent monitoring - NCBI/NIH
• Insulin sensitivity changes rapidly with improvement in the underlying condition - preemptively reduce rates by 10-20% when the patient starts recovering
• Always monitor potassium alongside glucose - insulin drives K+ intracellularly; hypokalemia is a common and dangerous complication
• Computerized decision-support tools (like EndoTool) reduce errors and achieve glycemic stability ~30% faster than paper-based protocols per 2024 SCCM data

Preparing a 50 mL Insulin Infusion (1 unit/mL)

What You Need

• Regular insulin (e.g., Actrapid / Humulin R) — 100 units/mL vial
• Normal saline (0.9% NaCl) — 50 mL bag or syringe
• Syringe, needle, aseptic technique

Calculation

Volume to draw = 50 units ÷ 100 units/mL = 0.5 mL of insulin

Step-by-Step Preparation

Verification Check

• Total insulin in bag: 50 units
• Total volume: 50 mL
• Concentration: 50 ÷ 50 = 1 unit/mL ✓

Infusion Rate Guide

Important Notes

• Use regular (short-acting) insulin only - never use NPH, glargine, or other long-acting insulins for IV infusion
• Insulin can adsorb to PVC plastic tubing - always pre-flush the line
• Prepare fresh every 24 hours (some institutions every 12 hours)
• Store at room temperature during use; discard unused portion after 24 hours
• Double-check with a second nurse/pharmacist before hanging (high-alert medication)