Weight-Based Heparin Drip Calculator

Standard weight-based heparin protocols

DVT/PE (full anticoagulation): bolus 80 units/kg IV (max 10,000 units), then continuous infusion at 18 units/kg/hr (max 2,000 units/hr). ACS/NSTEMI: bolus 60 units/kg IV (max 4,000 units), then continuous infusion at 12 units/kg/hr (max 1,000 units/hr). The two protocols come from different sources. The DVT/PE starting dose, 80 units/kg and 18 units/kg/hr, is the weight-based nomogram Raschke and colleagues published in 1993. The ACS dose, 60 units/kg and 12 units/kg/hr with its 4,000-unit and 1,000-units/hr caps, comes from the 2014 AHA/ACC guideline for non-ST-elevation acute coronary syndromes. The DVT/PE caps of 10,000 units and 2,000 units/hr are not part of the Raschke original, which dosed per kilogram only; they are common institutional caps, and yours may differ. Use your facility’s order set and nomogram, not this page, to decide the dose.

Worked example

75 kg patient with PE: bolus 80 × 75 = 6,000 units IV (under cap of 10,000). Drip rate 18 × 75 = 1,350 units/hr (under cap of 2,000). At standard concentration (25,000 units/250 mL = 100 units/mL), drip rate = 13.5 mL/hr.

aPTT monitoring

Check aPTT 6 hours after starting the drip and 6 hours after each rate change. Goal aPTT is institution-specific but typically 1.5-2.5 × control (50-80 seconds in many labs). Document each adjustment with the corresponding aPTT value.

For reference, this is the adjustment table from the original Raschke 1993 nomogram. It was calibrated to the aPTT reagents at the two study hospitals, and your lab’s therapeutic range is probably different, so use your facility’s nomogram at the bedside.

Source: Raschke RA et al., Ann Intern Med 1993. The 46 to 70 second band was that study’s therapeutic range.

Bleeding risk and reversal

Bleeding is the major adverse effect — monitor for hematomas, bleeding gums, hematuria, melena, dropping H/H. Reversal: protamine sulfate 1 mg per 100 units of heparin given in the last 4 hours, IV slow push, max 50 mg single dose. Watch for hypotension, bradycardia, anaphylaxis (especially in fish-allergic and protamine-allergic patients). HIT (heparin-induced thrombocytopenia) is a separate risk requiring monitoring of platelet count.

Running a heparin drip safely on a med-surg or telemetry unit

Heparin is one of the most error-prone medications nurses manage. The Institute for Safe Medication Practices has heparin on its list of high-alert medications for a reason: dosing errors land patients in ICU. The two errors I see most often: rate confusion between units/hr and mL/hr (especially when concentrations vary across pharmacy batches), and overlapping bolus doses when transferring between RNs at shift change. Always verify the concentration on the bag matches the pump library entry before starting or after every bag change. The most common in-house concentration is 25,000 units in 250 mL D5W (100 units/mL), but some facilities use 20,000 in 500 mL (40 units/mL) or 25,000 in 500 mL (50 units/mL). A patient on 1,800 units/hr is running 18 mL/hr at 100 units/mL but 36 mL/hr at 50 units/mL — same dose, different volume.

Independent double-check is required at every rate change, every bag swap, and every bolus dose. The ISMP-recommended double-check sequence: weight in kg, ordered units/kg/hr, calculated units/hr, programmed concentration on the pump, calculated mL/hr, actual pump display, line traced from bag to patient. Document the second nurse's name and the time. This adds 90 seconds to each adjustment and prevents tenfold dosing errors that have killed patients.

Anti-Xa vs aPTT monitoring

Many institutions are transitioning from aPTT to anti-Xa heparin assay because anti-Xa is more reproducible and less affected by lupus anticoagulant, factor deficiencies, and acute-phase reactants. Anti-Xa target for therapeutic UFH is typically 0.3–0.7 units/mL. The clinical bottom line for the bedside nurse: know which assay your facility uses, know its therapeutic range, and never compare aPTT and anti-Xa values directly — they measure different things. If your patient is bouncing between supratherapeutic and subtherapeutic on aPTT despite stable rates, ask the team about switching to anti-Xa monitoring; this is increasingly the standard for ICU and high-acuity patients.

HIT screening and the 4Ts score

Heparin-induced thrombocytopenia (HIT) is a delayed immune-mediated reaction that can paradoxically cause life-threatening clots. Onset is typically 5–10 days after heparin exposure (or within 24 hours if the patient was exposed in the previous 100 days). Watch for: platelet count drop ≥50% from baseline, new thrombosis on heparin, skin necrosis at injection sites, anaphylactoid reactions to IV heparin bolus. The 4Ts score (Thrombocytopenia severity, Timing, Thrombosis, oTher causes) stratifies probability. A score of ≥4 mandates stopping all heparin (including LMWH and flushes), starting a non-heparin anticoagulant (argatroban, bivalirudin, or fondaparinux per local protocol), and sending HIT antibody and serotonin release assay testing. Never restart heparin in a confirmed HIT patient — the antibodies persist for months and can trigger acute thrombosis on re-exposure.

Questions nurses ask

Sources

These are references for checking your math, not a protocol. Where your facility’s order set, nomogram or pump library says something different, follow it.

1. Raschke RA, Reilly BM, Guidry JR, et al. The weight-based heparin dosing nomogram compared with a “standard care” nomogram: a randomized controlled trial. Ann Intern Med 1993;119(9):874–881. doi.org/10.7326/0003-4819-119-9-199311010-00002
2. Amsterdam EA, Wenger NK, Brindis RG, et al. 2014 AHA/ACC guideline for the management of patients with non-ST-elevation acute coronary syndromes. Circulation 2014;130(25):e344–e426. doi.org/10.1161/CIR.0000000000000134
3. Institute for Safe Medication Practices (ISMP). High-alert medications in acute care settings. ecri.org: ISMP high-alert medications list