Background

In all cases, send blood for baseline FBC, coagulation screen, U&E’s and LFT’s before initiating therapy. Exercise caution with renal/liver patients as they will be at a higher risk of bleeding. Refer to Haematology SpR if patient has thrombocytopenia.

Baseline aPTT

Take a baseline aPTT – discuss with Haematology if not normal.

Bolus dose

bolus dose for patients who have not received heparin within the last 6 hours.

Preparation: Heparin Sodium Injection 1,000 units/ml.

Dose: prescribe 5000 units as stat dose: 5mls of 1,000 units/ml. If bolus dose is not to be administered or was administered previously (e.g. Cath Lab), the prescriber should sign in the administration chart to signify this.

iv continuous infusion

To make up the heparin syringe: dilute 25,000 units of heparin to 50mls (25,000 units heparin in 5mls and 45mls of 0.9% sodium chloride) to produce a concentration of 500 units/ml. Administer via a syringe pump.

  • Start the infusion at 2mls/hour (1,000 units/hour)
  • Check APTT ratio/APTT (sec) 4 hours after infusion start.
  • Sampling: Do not take coag. samples from lines or from veins proximal to the site of the heparin infusion, as this may lead to erroneous results.
  • Once 3 consecutive APTT results are returned within the target range, APTT monitoring can be extended to every 24 hours, if the patient’s clinical condition is stable.

Dosing for extremes of body weight

Dose adjustments to both the bolus dose and the initial infusion dose may be necessary at extremes of bodyweight (<50kg, >100kg). Please contact Consultant/Haematology in these cases.

Target Aptt range

  • The target APTT ratio is 1.5 – 2.5 (see corresponding APTT (sec) below).
  • A subset of this range may be appropriate in certain clinical scenarios e.g. high bleeding risk, severe DVT/PE. Contact Consultant/Haematology in these cases.
  • For a target range outside the recommended range, a different dose adjustment table must be prescribed.
  • If the APTT / APTT ratio is outside the normal range, adjust the Heparin Infusion as per Table 1 below.
  • A significant change in the patient’s clinical condition should prompt an immediate APTT determination, followed by dose adjustment if necessary.

Restarting after temporary break in infusion

If restarting infusion after a temporary break (e.g. procedure) restart at the rate that had achieved the target APTT as this is based on the individual patient’s response.

Administration chart

  • A Heparin Infusion Prescription Chart is available to document prescribing and administration of variable dosing of heparin.
  • If using the Heparin Infusion Prescription Chart, prescribe on the regular section: ‘heparin infusion - see separate infusion chart’

Heparin induced thrombocytopenia (HIT)

  • All patients who are to receive heparin should have a platelet count on the day of starting treatment.
  • For patients previously exposed to heparin in the last 100 days, obtain a platelet count 24 hours after starting heparin.
  • For all other patients, alternate day platelet counts should be performed from days 4 to 14 of therapy.
  • Signs of HIT include a 50% reduction of platelet count, thrombosis, or skin allergy.
  • If HIT is strongly suspected or confirmed, contact haematology.
  • Calculate the 4T score to determine if HIT testing is appropriate.

Dose adjustment table

Dose Adjustments to be made based on APTT Ratio / APTT (sec)
APTT Ratio# APTT sec)# Heparin Infusion Rate Change Recommended Recheck APTT (hours)
Above 6.6 Above 178 Stop the infusion for 1 hour, then reduce by 500 units/hour (↓ by 1ml/hour) 4
5.1 – 6.6 137 – 178 Reduce by 500 units/hour (↓ by 1ml/hour) 4
4.1 – 5.0 110 – 136 Reduce by 300 units/hour (↓ by 0.6ml/hour) 4
3.1 – 4.0 84 – 109 Reduce by 100 units/hour (↓ by 0.2ml/hour) 4
2.6 – 3.0 70 – 83 Reduce by 50 units/hour (↓ by 0.1ml/hour) 4
1.5 – 2.5 40 – 69 No change necessary if patient clinically stable 24*
1.2 – 1.4 33 – 39 Increase infusion by 200 units/hour (↑ by 0.4ml/hour) 4
Less than 1.2 Less than 33 Increase infusion by 400 units/hour (↑ by 0.8ml/hour) 4

#Use APTT Ratio if available. If not, use APTT (sec) and adjust dose accordingly.

* 3 consecutive APTTs must be returned within target range before monitoring intervals can be extended to every 24 hours.

Example

Worked Example 1:

Step 1: A patient weighing 60kg receives a bolus dose of 5000units equivalent to 5mls of Heparin 1,000 units/ml.

Step 2: The patient is started on the Heparin infusion of 2mls/hour

Step 3: The APTT ratio is measured 4 hours after the infusion is started. The APTT ratio target is 1.5 – 2.5. The APTT ratio returned is 2.9. Using Table 1, it is recommended to reduce the infusion by 0.1ml/hour i.e. From 2mls/hour to 1.9mls/hour. Check APTT 4 hours later.

Worked Example 2:

Step 1: A patient weighing 82kg receives a bolus dose of 5000units equivalent to 5mls of Heparin 1,000 units/ml.

Step 2: The patient is started on the Heparin infusion of 2mls/hour.

Step 3: The APTT ratio is measured 4 hours after the infusion is started. The APTT ratio target is 1.5 – 2.5. The APTT ratio returned is 1.3. Using Table 1, it is recommended to increase the infusion by 0.4ml/hour i.e. From 2mls/hour to 2.4mls/hour. Check APTT 4 hours later.