Heparin Drip Calculation Practice
Problem 1 · Heparin · Medium
Start a heparin drip using the weight-based protocol below. The patient weighs 176 lb. The bag holds 25,000 units in 250 mL, and the bolus vial is 1,000 units/mL. Platelets are 250,000/mm³. Find the bolus volume and the pump rate.
Protocol · weight-based heparin nomogram
aPTT (s)Action
Startno aPTT yetBolus 80 units/kg, then 18 units/kg/hr
Under 35< 1.2× controlRe-bolus 80 units/kg, increase 4 units/kg/hr
35–451.2–1.5×Re-bolus 40 units/kg, increase 2 units/kg/hr
46–701.5–2.3×No change
71–902.3–3×Decrease 2 units/kg/hr
Over 90> 3×Hold 60 min, then decrease 3 units/kg/hr
Recheck the aPTT 6 hours after every change. A sample protocol for practice — the facility’s protocol is the one you follow.
What the heparin problems use and how they are graded
Heparin drips are where dosage calculation stops being one formula. You convert the weight, work the bolus, start the drip in units/kg/hr, set the pump in mL/hr, and then change the rate from a table every time an aPTT comes back. This page walks each heparin problem through that chain one small step at a time.
It opens on heparin problems in the NurseSavvy dosage coach. Work it in the scratch pad and type your answer, or press "Walk me through it" and Tala, the dosage-calc nurse, asks one small question at a time and writes out the work in formula, ratio and proportion, or dimensional analysis. The protocol table sits under each problem.
- The protocol is the weight-based heparin nomogram published by Raschke and colleagues in 1993, the table most dosage-calculation textbooks reprint: an 80 units/kg bolus, a starting rate of 18 units/kg/hr, and an aPTT recheck 6 hours after every change.
- The adjustment rows are: aPTT under 35 seconds, re-bolus 80 units/kg and increase 4 units/kg/hr; 35–45, re-bolus 40 units/kg and increase 2; 46–70, no change; 71–90, decrease 2; over 90, hold 60 minutes and then decrease 3. The change is applied in units/kg/hr and converted back to units/hr and mL/hr.
- There are two kinds of heparin problem. Starting problems ask for the bolus volume and the pump rate; walked through, that is weight in kilograms, bolus units, bolus mL from the vial, starting units/hr, then mL/hr. Adjustment problems ask for the new pump rate; walked through, that is weight, which protocol row the aPTT falls in, any re-bolus or hold, the new units/kg/hr, units/hr, then mL/hr.
- Converting units/hr to mL/hr is the same D/H × Q setup as any dose: units/hr ordered, over the units in the bag, times the bag’s mL. Dimensional analysis shows it as a chain where units and kg cancel until only mL/hr is left.
- Rounding: kilograms to the tenth, units to the whole unit, bolus volume to the hundredth of a mL, and pump rates to the tenth of a mL/hr. A wrong step gets one more try with a hint, then the tutor shows the answer and the problem continues on the correct numbers.
- Real protocols differ: acute coronary syndrome dosing uses a smaller bolus and rate, many protocols cap the bolus or the dosing weight, and many hospitals titrate to anti-Xa levels instead of aPTT. On the unit, the facility protocol and the provider order rule, and heparin rate changes get an independent double check.
Why it works
Questions people ask
- How do you calculate a heparin drip rate in mL/hr?
- Multiply the weight in kilograms by the ordered units/kg/hr to get units/hr. Then divide units/hr by the units in the bag and multiply by the bag’s mL. For an 80-kg patient at 18 units/kg/hr with 25,000 units in 250 mL, that is 1,440 ÷ 25,000 × 250 = 14.4 mL/hr.
- How do you adjust a heparin drip from the aPTT?
- Find the row of the protocol table that contains the aPTT value, do any re-bolus or hold it lists, and add or subtract its rate change in units/kg/hr. Multiply the new units/kg/hr by the weight for units/hr, convert to mL/hr, and recheck the aPTT 6 hours later.
- Why is heparin dosed in units instead of mg?
- Heparin is measured by its biological activity, not its weight, so labels and orders use units. That is also why concentrations vary so much between products, from 10 units/mL flushes to 10,000 units/mL vials, and why reading the label carefully matters.
- Is this the protocol my hospital uses?
- Possibly not. These problems use one widely taught weight-based nomogram. Hospitals set their own bolus, starting rate, caps, and lab target, and some use anti-Xa levels instead of aPTT. The math steps are the same; the numbers in the table come from your facility protocol.
Keep going
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- GuideHow to Pass the Dosage Calculation Exam in Nursing SchoolMaster the six dosage problem types with one calculation method, step-level error correction, the unit conversions that cost points, and a practical two-week plan.