Overview
Heparin is a high-alert anticoagulant administered as a continuous IV infusion. If that phrase alone doesn't sharpen your focus, it should — high-alert means that errors with this drug carry a significant risk of patient harm.
Weight-based dosing protocols are the standard of care because they achieve therapeutic anticoagulation faster with fewer complications than fixed-dose approaches. This guide walks you through the complete workflow from the initial bolus through ongoing aPTT-based titration.
You're going to encounter heparin drips frequently in med-surg, telemetry, and critical care. Getting comfortable with these calculations now will serve you well throughout your career.
Standard Weight-Based Protocol
Concentration: 25,000 units in 500 mL NS = 50 units/mL Initial bolus: 80 units/kg IV push Initial infusion: 18 units/kg/hr Goal aPTT: 60-80 seconds (varies by facility)
Always verify your facility's specific protocol — the numbers above are a common standard but your hospital may differ slightly.
Worked Example: Initial Bolus
Your patient weighs 90 kg and the protocol calls for an 80 units/kg bolus. The heparin concentration is 50 units/mL. How much do you give?
Bolus dose: 80 units/kg x 90 kg = 7,200 units Volume to administer: 7,200 units / 50 units/mL = 144 mL (Or use a pre-filled syringe if your facility stocks them)
Give 7,200 units (144 mL from the bag). Note: many facilities cap the bolus at 10,000 units maximum regardless of weight. Always check your protocol.
Worked Example: Initial Infusion Rate
Same patient, 90 kg. The protocol starts at 18 units/kg/hr. What do you set the pump to?
Dose: 18 units/kg/hr x 90 kg = 1,620 units/hr Pump rate: 1,620 units/hr / 50 units/mL = 32.4 mL/hr
Set the pump to 32.4 mL/hr. Draw the first aPTT 6 hours after starting the drip.
aPTT Titration Protocol
Draw aPTT 6 hours after starting the drip, then adjust according to your facility's titration table. Here's a typical protocol:
aPTT < 35 sec: Re-bolus 80 units/kg, increase rate by 4 units/kg/hr. aPTT 35-59 sec: Re-bolus 40 units/kg, increase rate by 2 units/kg/hr. aPTT 60-80 sec: No change — therapeutic range achieved. aPTT 81-100 sec: Decrease rate by 2 units/kg/hr. aPTT > 100 sec: Hold drip for 1 hour, decrease rate by 3 units/kg/hr, recheck aPTT in 6 hours.
Every time you titrate, recalculate the new rate in mL/hr and document both the units/hr dose and the mL/hr pump rate.
Safety Reminders
Heparin is a high-alert medication — always require an independent double-check before starting or changing the rate. Monitor for signs of bleeding: hematuria, melena, petechiae, gum bleeding, excessive bruising. Know the antidote: protamine sulfate (1 mg neutralizes approximately 100 units of heparin given in the last 2-3 hours). Check platelets every 2-3 days for heparin-induced thrombocytopenia (HIT). Never mix heparin in the same line with incompatible drugs.
Watch for HIT
Heparin-Induced Thrombocytopenia (HIT) is a potentially life-threatening complication. If platelets drop by 50% or more from baseline, or fall below 150,000, suspect HIT. Stop the heparin immediately and notify the provider. This is not something to "watch and wait" on — early recognition saves lives.
Practice with NurseTally Calculators
Calculate heparin bolus and infusion rates quickly and accurately.