Question

You are caring for a patient who has had a RTKA yesterday. PMHX – hypothyroid, aortic valve replacement in 2010 for aortic regurgitation.

Medications at home: Warfarin, Levothyroxine

Post op medications include all the usual post-op total joint pain, nausea and bowel medications. This patient is also on Enoxaparin (Lovenox) SC bid since the evening they came back from the OR. Today the patient has been started on Warfarin at 1800 today.

1. What type of anticoagulant is Enoxaparin? Name other drugs in this family. How long will the effects last? How fast does it take effect? When a patient is on it, will you see a change in any lab data?
   
2. What type of anticoagulant is Warfarin? How long will the effects last? How fast does it take effect? When a patient is on it, will you see a change in any lab data?
   
3. Why would this patient be starting on Warfarin if they are already on Enoxaparin?
   
4. What lab data should you check and record in the MAR before giving the Warfarin?

Answer 1

RTKA stands for revisiontotal knee arthroplasty. It is also known as knee replacement surgery.

A total knee replacement is a surgical procedure whereby the diseased knee joint is replaced with artificial material. The knee is a hinge joint that provides motion at the point where the thigh meets the lower leg. The thighbone (or femur) abuts the large bone of the lower leg (tibia) at the knee joint.

During a total knee replacement, the end of the femur bone is removed and replaced with a metal shell. The end of the lower leg bone (tibia) is also removed and replaced with a channeled plastic piece with a metal stem. Depending on the condition of the kneecap portion of the knee joint, a plastic "button" may also be added under the kneecap surface. The artificial components of a total knee replacement are referred to as the prosthesis.The posterior cruciate ligament is a tissue that normally stabilizes each side of the knee joint so that the lower leg cannot slide backward in relation to the thighbone. In total knee replacement surgery, this ligament is either retained, sacrificed, or substituted by a polyethylene post. Each of these various designs of total knee replacement has its own particular benefits and risks.

Ans A. Enoxaparin is an anticoagulant that helps prevent the formation of blood clots. Enoxaparin is used to treat or prevent a type of blood clot called deep vein thrombosis (DVT), which can lead to blood clots in the lungs (pulmonary embolism).

In patients undergoing total knee replacement it is advised to receive 2.5 mg of apixaban orally twice daily or 30 mg of enoxaparin subcutaneously every 12 hours. Both medications were started 12 to 24 hours after surgery and continued for 10 to 14 days. Bilateral venography was then performed. The primary efficacy outcome was a composite of asymptomatic and symptomatic deep-vein thrombosis, nonfatal pulmonary embolism, and death from any cause during treatment. Patients were followed for 60 days after anticoagulation therapy was stopped.

Knee or hip replacement surgery

• 30 mg SC q12hr; initiate therapy 12-24 hr postoperatively; continue for 10 days, or up to 35 days postoperatively, or risk of DVT reduced significantly, or patient is on anticoagulant therapy
• For hip replacement surgery, may administer 40 mg SC qDay; initiate 9-15 hr preoperatively; continue for 10 days, or up to 35 days postoperatively, or until risk of DVT reduced significantly, or patient is on anticoagulant therapy

Medical patients with restricted mobility

• 40 mg SC qDay; continue until risk of DVT reduced significantly (6-11 days), or patient is on anticoagulant therapy.

• Knee or hip replacement surgery: Duration of administration is 7-10 days; up to 14 days has been administered in clinical trials or until risk of DVT has diminished.

Ans B. Warfarin- This medication is used to treat blood clots (such as in deep vein thrombosis-DVT or pulmonary embolus-PE) and/or to prevent new clots from forming in your body. Preventing harmful blood clots helps to reduce the risk of a stroke or heart attack. Conditions that increase your risk of developing blood clots include a certain type of irregular heart rhythm (atrial fibrillation), heart valve replacement, recent heart attack, and certain surgeries (such as hip/knee replacement).

Initial dose: 2 to 5 mg orally once a day
Maintenance dose: 2 to 10 mg orally once a day

Target INR: 2.5 (range: 2 to 3)

Duration of therapy: Indefinite

Ans C.Enoxaparin is used to prevent deep venous thrombosis, a condition in which harmful blood clots form in the blood vessels of the legs. These blood clots can travel to the lungs and can become lodged in the blood vessels of the lungs, causing a condition called pulmonary embolism. This medicine is used for several days after hip or knee replacement surgery, and in some cases following abdominal surgery, while you are unable to walk. It is during this time that blood clots are most likely to form. Enoxaparin is also used if you are unable to get out of bed because of a serious illness.

Enoxaparin is used together with warfarin to treat acute deep vein thrombosis with or without pulmonary embolism. It is also used to treat certain types of acute heart attacks.

Ans D. Prothrombin time (PT) — The clotting test used to measure the effect of warfarin is the prothrombin time (called pro time, or PT). The PT is a laboratory test that measures the time it takes for a clot to form. It is measured in seconds. It is particularly sensitive to the clotting factors affected by warfarin.