Heparin Dosing for Acute Arterial Occlusion
For acute arterial occlusion in a 70 kg adult, administer an 80 U/kg IV bolus (5,600 units) followed by an 18 U/kg/hour continuous infusion (1,260 units/hour), targeting an aPTT of 1.5-2.5 times control (approximately 50-70 seconds). 1
Rationale for Dosing Strategy
While the provided guidelines primarily address venous thromboembolism and acute coronary syndromes rather than acute arterial occlusion specifically, the most aggressive weight-based dosing regimen is appropriate for arterial occlusion given the immediate limb-threatening nature of this condition. The 80 U/kg bolus with 18 U/kg/hour infusion achieves therapeutic anticoagulation more rapidly than lower-dose regimens. 1, 2
Evidence Supporting Higher-Dose Regimen
The 80/18 dosing protocol achieves therapeutic aPTT significantly faster than 60/12 dosing, with 36% of patients reaching therapeutic range at 6 hours versus only 16.7% with lower dosing (p=0.03). 2
For venous thromboembolism, which requires similarly urgent anticoagulation, guidelines explicitly recommend 80 U/kg bolus followed by 18 U/kg/hour infusion with aPTT target of 1.5-2.5 times control. 1
The lower 60/12 dosing regimen recommended in cardiac guidelines has maximum caps (4,000 U bolus, 1,000 U/hour infusion) that are specifically designed for patients >70 kg receiving concurrent fibrinolytics or undergoing PCI, where bleeding risk is substantially elevated. 1, 3, 4
Practical Dosing for 70 kg Patient
Initial bolus: 5,600 units IV push
Continuous infusion: 1,260 units/hour initially
Monitoring Requirements
Check aPTT at 3,6,12, and 24 hours after initiation, then 4-6 hours after any dose adjustment. 4, 5
Target aPTT: 1.5-2.5 times control (approximately 50-70 seconds), corresponding to anti-factor Xa levels of 0.3-0.7 IU/mL. 1
Daily platelet counts throughout the entire course of therapy to detect heparin-induced thrombocytopenia, which occurs in up to 5% of patients receiving UFH. 1, 4
Critical Caveats
Do not apply the cardiac guideline dose caps (4,000 U bolus maximum, 1,000 U/hour maximum) to acute arterial occlusion unless the patient is receiving concurrent fibrinolytics. These caps were established specifically for STEMI patients receiving thrombolytics where bleeding risk is markedly elevated. 1, 3
Weight-based dosing is essential because body weight is the strongest predictor of heparin effect on aPTT, and fixed-dose regimens result in suboptimal anticoagulation. 3, 6
Underdosing is common and dangerous in this population—studies show 89% of patients receive inadequate bolus doses and 76% receive inadequate infusion rates, leading to delays in achieving therapeutic anticoagulation exceeding 24 hours in 29% of cases. 7
Duration of Therapy
Continue infusion for 48 hours minimum or until definitive intervention (surgical thrombectomy, catheter-directed thrombolysis, or revascularization procedure). 1, 5
Do not routinely extend beyond 48 hours unless ongoing indications exist (recurrent ischemia, inability to proceed with definitive intervention), as prolonged infusions increase HIT risk without additional benefit. 5
Alternative Considerations
If renal function is preserved (CrCl >30 mL/min), LMWH (enoxaparin 1 mg/kg subcutaneously every 12 hours) is an acceptable alternative that does not require aPTT monitoring and may reduce major bleeding risk compared to UFH. 1, 8
For patients with known or suspected HIT, use bivalirudin (0.25 mg/kg bolus followed by 0.5 mg/kg/hour infusion) or argatroban instead of heparin. 1, 4