Unfractionated Heparin by Infusion
Loading dose 5000 units IV over 5 min Infusion 20,000 units made up in saline to 40 mL (500units/mL). Start the infusion using a syringe pump: | ||
| Patient weight (kg) | Heparin dose (480units/kg/day) | Heparin infusion rate (mL/h) |
| >70 | 33,600 | 2.8 |
| 60 | 28,800 | 2.4 |
| 50 | 24,000 | 2.0 |
Check the activated partial thromboplastin time (APTT) at 4–6h. Ensure that the request form clearly states the patient is receiving heparin. Adjust the dose as follows: | ||
| Activated partial thromboplastin(APTT) time (target 1.5–2.5×control) | Action | |
| >5 | Stop for 1h then reduced infusion rate by 1.0 mL/h. | |
| 4.1–5 | Reduce infusion rate by 0.6 mL/h | |
| 3.1–4 | Reduce infusion rate by 0.2 mL/h. | |
| 2.6–3 | Reduce infusion rate by 0.1 mL/h. | |
| 1.5–2.5 | No change. Recheck APTT in 10h | |
| 1.2–1.4 | Increase infusion rate by 0.4 mL/h. | |
| <1.2 | Increase infusion rate by 0.8 mL/h. | |
After each change in infusion rate, recheck APTT in 4–6h, and every 24h if stable.
Check the platelet count daily. Heparin-induced thrombocytopenia (HIT), which may be complicated by thrombosis, is most likely to occur 5–10 days after starting heparin. Stop heparin immediately and take advice from a haematologist if there is a significant fall in platelet count. See p. 580 Table 102.3 and p. 582 appendix 102.3 for further information on the diagnosis of HIT.