What is the deal with clots…?
Anticoagulation therapy is used a in a number of different types of patients. The frequent use of anticoagulant therapy in surgical patients, particularly orthopedic and heart surgeries means that health care providers should have a relatively good and in-depth understanding of anticoagulants, why they are used and what they do.
Anticoagulation therapy is used primarily to prevent the formation of deep vein thrombosis (DVT) as a serious complication of DVT is of course pulmonary embolism (PE).
DVT is a serious and potentially life threatening situation. There are three factors that are known to cause DVT: vessel wall damage, venous stasis, and hypercoagulability. Damage to the vessel walls can cause DVT because the body will respond to damage with the standard clotting cascade which ultimately results a fibrin clot in the vascular system. Venous stasis caused by pooling of blood, which may occur in a situation where a limb is dependant or in individuals with poor venous return resulting in edematous extremities. Hypercoagulabilty can cause DVT if the body is over reactive to insult and frequent clots are formed. DVT complicates because there is a potential risk that the thrombosis dislodges and results in an embolism, causing PE.
Anticoagulation therapy can be used to either help to dissolve a clot that is present (thrombolytic agents, save this for later) or prevent further clots from forming.
...Here's looking at some commonly used medications...
Heparin binds with antithrombin III, which will enhance the inactivation of thrombin, Xa, and XIa (clotting factors). Because thrombin is required in the body for the conversion of fibrinogen into fibrin, the absence of thrombin results in an absence of fibrin, and therefore clots are unable to form. Low doses of heparin will inhibit Xa therefore inhibiting the conversion of prothrombin into thrombin. High doses of heparin act directly on the thrombin by inactivating it, preventing fibrin formation.
Heparin may be administered with an initial bolus followed by a continuous infusion. It is incredibly important for the individual who is administering this to be aware of the partial thomboplastin time (PTT) or aPTT lab values. These are taken depending on hospital policy, but roughly every 6 hours following the initial bolus.
Heparin is given by the subcutaneous (SC) or intravenous (IV) route only. Heparin given intramuscularly (IM) can cause hematoma, irritation, and pain.
Overdosing heparin will make you at risk for hemorrhage and death. Therefore, it is also important to know that the antidote for heparin is Protamine Sulphate. Heparin’s onset is immediate (IV) so in the event of overdose stopping the infusion may be an effective intervention (follow up with PTT).
Warfarin works to anticoagulant in a different way that heparin. Warfarin and heparin can be given simultaneously because they do work in different ways. Where heparin works directly on the clotting cascade, warfarin actually works by inhibiting vitamin K, therefore having a more indirect effect on coagulation. By interfering with the liver’s ability to synthesize vitamin K-dependent clotting factors, the clotting cascade is interrupted.
Warfarin is an oral anticoagulant. There is conflicting data as to warfarin’s onset, but it is generally accepted that the time required to reach therapeutic levels is approximately 24-72 hours.
The lab value that you should be aware of when giving warfarin therapy is the INR. The INR is the “international normalized ratio.” It is a ratio of the recipient’s prothombin time (PT) compared to a normal PT.
Low molecular weight heparin
Enoxaparin works by inhibiting factor Xa, therefore inhibiting prothrombin into thrombin and therefore inhibiting fibrinogen into fibrin. This drug is used in orthopedic patients. The FDA approved this drug for prevention of clots in knee and hip surgeries.
Enoxaparin is a relatively new drug. It is given SC mainly to the abdomen. Injections given to the flank may limit the health care providers ability to assess the site for complications if the recipient is positioned supine. Rotate the sites as per hospital policy.
Normal dosage is 30mg given twice a day. Lovenox comes in a pre-filled glass syringe directly from the manufacturer.
Enoxaparin will not affect PT or PTT lab values because the chemical structure of this drug will not bind with many plasma proteins so there is a more predictable dose.