Overview
Insulin is classified as a high-alert medication, and for good reason — dosing errors can cause life-threatening hypoglycemia or dangerous hyperglycemia. You'll administer insulin on virtually every shift in acute care, so getting comfortable with these calculations is essential.
This guide covers the three main insulin dosing scenarios you'll encounter: sliding scale coverage, correction dose calculations, and continuous insulin infusions.
Reading a Sliding Scale
A sliding scale provides dose instructions based on the patient's blood glucose (BG) level. The scale is ordered by the provider and varies by patient. Here's a typical example:
BG 150-199: Give 2 units. BG 200-249: Give 4 units. BG 250-299: Give 6 units. BG 300-349: Give 8 units. BG 350-399: Give 10 units. BG 400 or above: Give 12 units and notify the provider.
Always verify: which insulin (Regular? Lispro? Aspart?), which route (subQ is standard for sliding scale), and the BG recheck interval.
Correction Dose Formula
Correction Dose = (Current BG - Target BG) / Correction Factor
The correction factor (also called insulin sensitivity factor) is typically between 20-50 for most patients. It represents how much 1 unit of insulin will lower blood glucose.
Worked Example: Correction Dose
Your patient's BG is 320 mg/dL. The target BG is 150 and the correction factor is 30. How much insulin do you give?
Correction dose = (320 - 150) / 30 = 170 / 30 = 5.67
6 units (round to the nearest whole unit for subQ insulin). Always verify the rounding rule with your facility's protocol.
Insulin Drip Protocol
Continuous insulin infusions are used for DKA, HHS, and perioperative glucose management. The standard concentration makes the math beautifully simple:
Standard mix: 100 units Regular insulin in 100 mL NS = 1 unit/mL. This means mL/hr = units/hr. If the order says "run at 4 units/hr," you set the pump to 4 mL/hr. No conversion needed.
Titration is typically based on hourly BG checks, with adjustments of 0.5-1 unit/hr at a time. Most protocols target BG 140-180 mg/dL in critically ill patients.
Insulin Safety — Non-Negotiable Rules
Always require an independent double-check before administering insulin. Never abbreviate "units" as "U" — it can be misread as a zero, turning 4 units into 40. Check BG before every dose and at ordered intervals during drips. Know the signs of hypoglycemia: tremors, diaphoresis, confusion, BG < 70 mg/dL. Have dextrose (D50 or D10) readily available whenever insulin is infusing. Insulin drips require hourly BG monitoring — no exceptions.
Treating Hypoglycemia
If BG drops below 70 mg/dL: for a conscious patient, give 15 g of fast-acting carbs (4 oz juice, 3-4 glucose tablets) and recheck in 15 minutes. For an unconscious patient or one who can't swallow, give D50 25 mL IV push (12.5 g dextrose) or glucagon 1 mg IM. Recheck BG in 15 minutes. Remember the Rule of 15: 15 grams, recheck in 15 minutes.
Practice with NurseTally Calculators
Calculate insulin doses and verify sliding scale interpretations.