Welcome back to UH EMS-I’s Pharmacy Phriday. In the past two installments, we reviewed antiplatelets used within the UH protocols for confirmed STEMIs. In this installment, we will also review the use of an anticoagulant, heparin, within that protocol. Both types of medication help to meet the treatment goal in an acute myocardial infarction (MI) by reducing clotting and limiting the size of the infarcted area, but in different ways.
As mentioned previously, both are often referred to as “blood thinners,” though neither actually thin the blood. Antiplatelets interfere with the binding of platelets, the process that forms what is called a platelet plug. Anticoagulants, heparin being one of them, interfere with the proteins, or factors, in the blood that are involved with the coagulation process. Different anticoagulants interfere with different factors to prevent clotting.
While aspirin and ticagrelor, two medications reviewed in previous weeks, work on the platelets, heparin rapidly inactivates thrombin, which normally causes the formation of fibrin. Blocking this cascade prevents the formation of clots and prolongs the clotting time of blood. The early use of heparin in the prehospital setting helps to reduce the size of the infarct and in turn, is associated with improved survival of the MI patient.
Heparin is a high-risk medication and can potentially cause severe bleeding. The medication is usually guided by anticoagulation lab studies (PT and PTT). Although these tools are unavailable in the prehospital setting, the use of heparin in certain cases has proven benefits that exceed the risks of starting therapy without these baseline studies. Monitoring and maintenance dosing are often implemented as the patient’s care continues in the hospital setting.
Because of its possible side effect of bleeding, heparin should not be given to anyone with active bleeding or a trauma or stroke patient. UH protocols do not allow the administration of heparin in cases of a stimulant-induced STEMI, in a pediatric patient, for pregnant women, in cases of hypertension, when a patient has had surgery within the last 14 days, or in cases of aortic dissection. Some texts also suggest caution in its use with the elderly and chronic alcoholic patients.
Heparin should not be administered if the patient is already taking an anticoagulant such as Warfarin, Eliquis, Xarelto, Pradaxa, etc. A list of common anticoagulant medications is provided in the protocol’s “key points” for reference. When questioning a patient about their medications, the provider should ask specifically about “blood thinners,” anticoagulants, or direct-acting oral anticoagulants (DOACs).
As referenced last week, a STEMI checklist is a part of the protocol and should be reviewed before administering ticagrelor or heparin. Items included in the checklist are:
- No sharp ripping/tearing chest or back pain
- No altered mental status
- No known bleeds or concern of bleeding (i.e., GI bleeds, vomiting blood, blood in urine, etc.)
- No trauma or CPR
- No severe headache
- If STEMI mimickers are present, the provider must consult medical direction
As was mentioned with the use of ticagrelor, heparin is approved in the UH protocols for administration in a confirmed STEMI. Remember: when in doubt, contact medical direction.
Dosing for heparin is a one-time dose of 60 units/kg given IV/IO, with a maximum dose of 4000 units (this is the equivalent of a patient that weighs 147 lbs.). Be alert! Heparin is normally provided in a 1 ml vial that contains 5000 units. The maximum dose allowed per the protocols would equal just 0.8 ml of that concentration.
Be sure to check out the “Where Is It?” pictures below. You’ll note that you will find heparin in the same general vicinity as aspirin and ticagrelor. Medications used within a specific protocol are often stored close together in the drug box. This is an intentional design by UH staff to assist the provider in the field, as well as attempt to reduce the risk of medication errors.
Till the next edition of Pharmacy Phriday, stay safe!
