Randomized drip problems using real premixed bag strengths: heparin 25,000 units in 250 or 500 mL and 20,000 units in 500 mL, and regular insulin 100 units in 100 mL. Work units/hr into a pump rate, read a running drip back into units/hr, and on Hard, calculate a weight-based heparin bolus and starting rate.
Find the concentration in units/mL, then divide the ordered units/hr by it. Heparin 25,000 units in 250 mL is 100 units/mL, so an order of 1,000 units/hr runs at 1,000 ÷ 100 = 10 mL/hr. To go the other way, multiply: 18 mL/hr × 100 units/mL = 1,800 units/hr.
Get the concentration first, every time. The same order runs at very different rates depending on the bag: 1,000 units/hr is 10 mL/hr from a 100 units/mL bag but 20 mL/hr from a 50 units/mL bag.
| Order | Setup | Answer |
|---|---|---|
| 1,000 units/hr; 25,000 units/250 mL | 100 units/mL; 1,000 ÷ 100 | 10 mL/hr |
| 1,200 units/hr; 25,000 units/500 mL | 50 units/mL; 1,200 ÷ 50 | 24 mL/hr |
| Running at 18 mL/hr; 25,000 units/500 mL | 18 × 50 | 900 units/hr |
| 80 kg; bolus 80 units/kg, then 18 units/kg/hr; 25,000 units/250 mL | Bolus 80 × 80 = 6,400 units; 80 × 18 = 1,440 units/hr ÷ 100 | 6,400 units; 14.4 mL/hr |
| 172 lb; 18 units/kg/hr; 25,000 units/500 mL | 172 ÷ 2.2 = 78.2 kg; × 18 = 1,408 units/hr ÷ 50 | 28.2 mL/hr |
In the last example, carrying the unrounded weight (78.18 kg) through gives 1,407 units/hr and 28.1 mL/hr. Both are taught, so the practice tool accepts either and tells you which path it used. If your facility's protocol rounds heparin to the nearest 10 or 100 units, set that in the rounding options.
| Order | Setup | Answer |
|---|---|---|
| 6 units/hr; 100 units/100 mL | 1 unit/mL; 6 ÷ 1 | 6 mL/hr |
| 4 units/hr; 100 units/250 mL | 0.4 units/mL; 4 ÷ 0.4 | 10 mL/hr |
| 0.1 units/kg/hr; 72 kg; 100 units/100 mL | 72 × 0.1 = 7.2 units/hr | 7.2 mL/hr |
| Running at 12.5 mL/hr; 100 units/250 mL | 12.5 × 0.4 | 5 units/hr |
With the 1 unit/mL premix, units/hr and mL/hr are the same number, which is one reason that concentration is popular. With a 0.4 units/mL bag they are not. A student who sets 4 mL/hr for an order of 4 units/hr delivers only 1.6 units/hr, well under half the ordered dose.
Weight-based heparin protocols trace back to the Raschke nomogram, which started with an 80 units/kg bolus and 18 units/kg/hr and adjusted the rate by aPTT. Facilities now use their own protocols, with different bolus sizes, starting rates, monitoring tests and rounding. The practice problems vary these numbers on purpose, so you learn the method rather than one protocol.
For insulin, the 2024 consensus on hyperglycemic crises describes a fixed-rate infusion of 0.1 units/kg/hr for DKA and 0.05 units/kg/hr for HHS. Real protocols adjust from there by glucose, and that adjustment is a clinical decision, not an arithmetic one.
IV heparin and IV insulin are both on ISMP's list of high-alert medications. In practice, every rate change gets an independent double-check, and the pump's drug library is set up to catch rates outside safe limits. On paper, the check is yours: a heparin drip running at 280 mL/hr or an insulin drip at 0.2 mL/hr means something in the setup went wrong.
Divide the units in the bag by its volume to get units/mL, then divide the ordered units/hr by that concentration. 1,000 units/hr from 25,000 units in 250 mL (100 units/mL) runs at 10 mL/hr.
Multiply the rate in mL/hr by the concentration in units/mL. A 25,000 units/500 mL bag (50 units/mL) running at 18 mL/hr delivers 900 units/hr.
Multiply the weight in kg by the ordered units/kg. 80 kg at 80 units/kg is 6,400 units. Use the bolus amount and starting rate in the order or your facility protocol, not a remembered number.
Divide the ordered units/hr by the bag concentration in units/mL. With 100 units in 100 mL (1 unit/mL), 6 units/hr is 6 mL/hr. With 100 units in 250 mL (0.4 units/mL), 4 units/hr is 10 mL/hr.