Heparin precautions

1.   Draw aPTT at steady state

When the aPTT is checked at 6 hours or longer after a dosage change, steady-state kinetics can be assumed.  Non-steady-state analysis can lead to erroneous dosing calculations.

2.   Adjust dosages cautiously

Dosage changes must be made slowly, and the aPTT must be checked every six hours until stable, then daily during the course of therapy. Close monitoring of the patient is essential. Since the aPTT response to changes in heparin infusion rates is not always linear the dosage adjustments should be made in small increments of 100-200 units/hr.

Heparin dose is clearly the most important determinant of minor bleeding episodes. When examined on a unit-per-kg per-hour basis, there is over a 3-fold increase in the risk of bleeding in patients receiving 25 units/kg/hr as compared to patients who receive 15 units/kg/hr.

Aging is a risk factor for total and major bleeding complications.  Because of age-related changes in pharmacokinetic characteristics of heparin, aging is associated with an increase in heparin levels after standard doses.  Heparin dose requirements are decreased in the elderly.

3.   The major risk factors for hemorrhage from heparin therapy are:

•        Age over 60

•        Recent surgery

•        Trauma (or risk of trauma)

•        Severe hypertension

•        Peptic ulcer disease (or history of ulcers)

•        Drugs which inhibit platelet function.

•        Presence of any potential bleeding site

•        Congenital or acquired hemostatic defect

•        Severe renal failure

•        Severe hepatic failure

4.   Reversal of heparin effects

Minor bleeding

•        Stop heparin

•        Monitor vital signs, aPTT, Hgb, Hct, platelet count.

  Major bleeding

•        Stop heparin

•        Monitor vital signs, aPTT, Hgb, Hct, platelet count.

•        Give blood transfusions as necessary

•        Consider protamine reversal of heparin.

  Protamine

•        Protamine rapidly neutralizes heparin's anticoagulant activity.

•        In the event of a critical bleed, 1mg of protamine will neutralize approximately 100 units of heparin.

•        Protamine can cause severe, anaphylactoid reactions, use only when severe bleeding warrants it.

5.   Heparin- induced thrombocytopenia

Standard unfractionated heparin can cause an antibody-mediated (Type II) thrombocytopenia in 3-4% of patients who receive heparin for longer than 7 days.  When the platelet count falls precipitously, stop heparin.  Do not start low-molecular-weight heparin, it will cross-react with the antibody 90% of the time.  If a rapidly acting anticoagulant is needed, substitute the recombinant hirudin known as lepirudin.

See also:

Introduction

Monitoring parameters

Pharmacokinetic formulas

Bibliography