One of the most critical and often overlooked steps in insulin CRI preparation is running 50 mL of the solution through the IV line before connecting to the patient. Insulin adsorbs to PVC and polyethylene tubing, and failure to prime the line can result in significantly reduced insulin delivery for the first 30-60 minutes. The Insulin CRI Calculator walks through each preparation step, and the DKA Management Calculator integrates insulin CRI into the overall DKA protocol.
Only regular insulin (e.g., Humulin R, Novolin R) should be used for continuous rate infusions. Regular insulin is the only insulin formulation approved and safe for IV administration. Its characteristics make it ideal for CRI use:
Onset: 10-30 minutes IV (immediate onset compared to subcutaneous formulations).
Peak: 30-60 minutes IV.
Duration: 1-4 hours IV (short duration allows precise dose titration).
Other insulin types (NPH, glargine, detemir, PZI) are formulated for subcutaneous use only. They contain additives (protamine, zinc) that alter absorption and can cause severe adverse reactions if given IV. Glargine in particular precipitates at neutral pH (it is formulated at pH 4.0) and must never be administered intravenously.
Warning: Using the wrong insulin type for a CRI is a potentially fatal medication error. Always verify the label reads "Regular" insulin before IV administration. Regular insulin vials typically have a clear solution (not cloudy). NPH insulin is cloudy/turbid due to protamine-zinc suspension. If the insulin is cloudy, do NOT use it for IV CRI.
Follow these steps precisely for safe and accurate insulin CRI preparation:
Step 1 — Calculate the insulin dose:
Dogs: 2.2 U/kg body weight. Example: 20 kg dog = 2.2 × 20 = 44 units of regular insulin.
Cats: 1.1 U/kg body weight. Example: 5 kg cat = 1.1 × 5 = 5.5 units of regular insulin.
Step 2 — Add insulin to a 250 mL bag of 0.9% NaCl: Using a U-100 insulin syringe, draw up the calculated dose and inject it into a 250 mL bag of normal saline. Mix gently by inverting the bag several times. Do not shake vigorously, as this can denature the insulin protein.
Step 3 — Label the bag clearly: Include patient name, insulin type and dose, date and time of preparation, concentration, and initials of the person who prepared it.
Step 4 — Prime the IV line: Connect the administration set and run 50 mL of the insulin solution through the line before connecting to the patient. Discard this priming volume. This saturates the insulin binding sites on the tubing. Failure to prime results in up to 20-30% less insulin delivery in the first hour.
Step 5 — Start the infusion at 10 mL/hr using an IV infusion pump (never run insulin CRI on gravity drip).
After starting the insulin CRI at 10 mL/hr, adjust the rate based on blood glucose measurements taken every 1-2 hours:
| Blood Glucose (mg/dL) | Insulin CRI Rate | Additional Actions |
|---|---|---|
| >250 | 10 mL/hr (maintain) | Continue current protocol; monitor Q1-2H |
| 200-250 | 7 mL/hr | Consider adding 2.5% dextrose to maintenance fluids |
| 150-200 | 5 mL/hr | Add 2.5-5% dextrose to maintenance fluids |
| 100-150 | 3 mL/hr | Ensure 5% dextrose in fluids; monitor closely |
| <100 | STOP insulin CRI | Bolus dextrose if symptomatic; restart CRI when BG >150 |
The Insulin CRI Calculator provides these rate adjustment recommendations automatically based on entered blood glucose values.
Awareness of common errors prevents dangerous medication mistakes:
Using the wrong insulin type: As discussed, only regular insulin is safe for IV use. This is the single most dangerous error.
Forgetting to prime the line: Results in subtherapeutic insulin delivery for the first 30-60 minutes, delaying glucose reduction and ketosis resolution. Some facilities use non-PVC tubing to reduce adsorption.
Using the wrong syringe: U-100 insulin syringes are calibrated for 100 units/mL insulin. Using a standard syringe (mL markings) with U-100 insulin can result in 10-fold dosing errors. Always use insulin-specific syringes.
Incorrect math: Double-check all calculations. Have a second team member independently verify the dose, volume, and preparation before starting the infusion. The Insulin CRI Calculator provides an independent verification tool.
Running without a pump: Insulin CRI must always run on a calibrated infusion pump. Gravity administration does not provide the precision needed for safe insulin delivery. Even small rate variations can cause dangerous hypoglycemia or inadequate treatment.
Thorough documentation is essential for insulin CRI management, especially during shift changes. Record: the preparation details (units added, bag volume, date/time, preparer), line priming confirmation, starting rate and all subsequent rate changes with corresponding blood glucose values, potassium levels and supplementation adjustments, dextrose additions to fluids, and any adverse events (hypoglycemia episodes, arrhythmias).
A dedicated insulin CRI flowsheet or treatment sheet column makes it easy for the incoming team to understand the patient's trajectory and continue the protocol seamlessly. Many practices use a standardized DKA management form that tracks all four pillars (fluids, insulin, K+, dextrose) simultaneously.
Insulin CRI bags should be replaced every 24 hours, as insulin stability in saline decreases over time. Always prepare a fresh bag daily, repeating the line-priming step with the new bag. Label old bags clearly before disposing of them per your clinic's pharmaceutical waste protocol.
- Only regular insulin (clear solution) is safe for IV CRI; never use NPH, glargine, detemir, or PZI intravenously.
- Dose: 2.2 U/kg (dogs) or 1.1 U/kg (cats) added to 250 mL 0.9% NaCl; start at 10 mL/hr.
- Always prime the line by running 50 mL through before connecting to the patient; insulin adsorbs to tubing.
- Adjust rate based on blood glucose: maintain at 10 mL/hr if BG >250; reduce stepwise as glucose drops; stop if BG <100.
- Use a calibrated infusion pump for all insulin CRI; never use gravity administration.
- Double-check all calculations with a second team member; replace insulin bags every 24 hours.