Dosage Calculation · Topic 9 of 10
Continuous Infusion Calculations
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Continuous Infusion Calculations
Turn an ordered dose into the pump's mL/hr: dose per hour ÷ concentration. Heparin, insulin and vasopressor drips are high-alert, so a math slip harms fast.
The formula, step by step
The pump only knows mL/hr
Worked example: heparin (per hour)
1,000 units/hrPer-hour order, so no × 60.
Worked example: mcg/kg/min
5 mcg/kg/minWeight-based heparin (units/kg/hr)
Already per hour — no × 60
A common nomogram starts with an 80 units/kg IV bolus, then 18 units/kg/hr (70 kg: 5,600-unit bolus, 1,260 units/hr = 25.2 mL/hr at 50 units/mL). A +2 units/kg/hr change at 70 kg adds 140 units/hr: 1,400 units/hr = 28 mL/hr. Protocol-specific; obese patients have capped doses.
Common errors
Most drip errors are × 60 or × 1,000 slips
At the bedside
Math errors are caught on paper — these show up in the patient
Lower the insulin rate for a steep fall even if one glucose value looks fine. For hypoglycemia: treat per protocol and notify the provider. Teach the patient not to adjust the pump and to report bleeding (heparin) or shakiness and sweating (insulin) right away.
Monitor while it runs
Many units use an anti-Xa nomogram instead of aPTT — follow the protocol. In DKA the usual goal is a glucose fall of about 50–75 mg/dL per hour on the insulin drip.
mL/hr = dose per hour ÷ concentration. Only per-minute orders get × 60 — and every heparin, insulin or vasopressor drip gets an independent double-check.
Sources · Pharmacology for Nurses 2.4 Dosage Calculations (OpenStax) · Nursing Dosage Calculations: Introduction to mcg/kg/min (WisTech Open) · Heparin (StatPearls) · Heparin Sodium Injection Label (DailyMed) · Pharmacology for Nurses 20.2 Anticoagulants (OpenStax) · Independent Double Checks (ISMP) · Distributive Shock (StatPearls) · Diabetic Ketoacidosis (StatPearls) · Hyperglycemic Crises in Adults With Diabetes: A Consensus Report (ADA/EASD 2024, Diabetes Care) · Medical-Surgical Nursing 21.2 Diabetes Mellitus (OpenStax) · Hyperglycemic Crises in Adult Patients With Diabetes (ADA 2009, Diabetes Care) · Follow your facility's protocol for high-alert infusions.
Continuous Infusion Calculations
Continuous IV drips run high-alert drugs — heparin, insulin, and vasopressors — at a calculated, titrated rate. Converting the order into a pump rate and re-titrating to the trend is the tested skill.
Continuous IV infusions deliver high-alert drugs (heparin, insulin, norepinephrine and other vasopressors) at a precisely titrated rate. The core skill is converting an ordered dose into a pump rate in mL/hr using the drug concentration, then re-titrating that rate to a target lab or hemodynamic value (aPTT, blood glucose, MAP). Weight-based drips (units/kg/hr or mcg/kg/min) require the patient weight in kilograms and a x60 min/hr conversion before dividing by concentration.
Key Distinctions
Pump rate (mL/hr) = ordered dose per hour divided by concentration (units or mcg per mL). For per-minute orders, multiply by 60 (mcg/kg/min x kg x 60 = mcg/hr) before dividing. Titrate heparin to aPTT, insulin to the glucose trend (the rate of fall, not a single value), and vasopressors to MAP within the protocol dose ceiling. High-alert drips require an independent double-check of dose and pump settings.
Clinical Pearl
The pump speaks mL/hr, the order speaks dose — convert, double-check, then titrate to the trend (aPTT, glucose, MAP), never to a single number.
Knowledge Check
3 quick questions on the must-knows for this topic.
A continuous IV pump rate is expressed in what unit?
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Go further
- SimulatorDosage Calculation CoachDosage calculation word problems with a big answer box, and a tutor who walks you through the steps when you want it. Calculator and conversions included.
- GuideDosage Calculation Practice Questions With AnswersWork nearly 90 numeric-entry dosage problems with a step-by-step tutor: doses, conversions, IV and drip rates, pediatric safe ranges, reconstitution, heparin, and insulin.
- SimulatorHeparin Drip Calculation PracticeWork heparin drip problems step by step: weight-based bolus, starting rate, and aPTT adjustments read off a nomogram, in the method you use.
- GuideIV Drip Rate and Infusion Calculations ExplainedCalculate mL/hr, gtt/min, mcg/kg/min, and heparin units/kg/hr drips with units that expose conversion errors before they reach the answer box.
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