Preventing Blood Clots After Surgery
What measures are taken to reduce the risk of blood clots?
We routinely use a blood-thinning medicine called warfarin. This drug, or an alternative blood thinner, will be taken for about four weeks after surgery to lower the risk of a blood clot. The hospital pharmacist will monitor the blood-thinner dose, and will advise you if there is any change in the dosage. After leaving the hospital, you will have a blood test twice a week, or more if necessary, to monitor the ef-ficacy of the blood-thinner.
In addition, the exercises, foot pumps, lack of a tourni-quet, efficient surgery, and early walking after surgery all serve to minimize the risk of blood clots. We thus use a multi-modal program to reduce the risk of blood clots forming.
What more should I know about blood clots?
Any surgery increases the risk of blood clot formation. Some patients are genetically predisposed to clot for-mation and are at a higher risk. If you have ever had clots in the past, please be sure to let us know.
Clots can cause serious problems such as heart or vas-cular disease, or a stroke. A lung injury can occur if the clot migrates to your lungs from the leg. A large enough clot migrating to the heart or lungs can be fatal.
Anticoagulation (blood-thinning) therapy is recom-mended after all knee replacement operations to re-duce the likelihood of developing a clot. Even if a clot develops in the leg, if you are on a blood-thinner, the risk of the clot enlarging and migrating to the lungs is reduced. Exercises, spinal anesthetics, early mobili-zation, intermittent foot pumps, and blood-thinning medications are all aimed at reducing the risk of blood-clot formation after surgery.
What should I know about the blood-thinning medicine that I will be given?
The most common blood thinner used after knee re-placement is the drug warfarin. It is an inexpensive medication that requires adjustment on the dosage for each patient.You will take warfarin at the same time each day. The dose will be based on a blood test that measures how fast your blood clots. The results are recorded as PT (prothrombin time) and INR (international normalized ratio); the pharmacist will look at these test results and figure out how much warfarin you should take. The goal of taking warfarin is to keep your INR between 1.8 and 2.5. If you miss a dose of warfarin, take it as soon as you remember, but do not double the next dose.
Many things, such as diet, other medications, physi-cal activity and illness can affect warfarin dosing. Vi-tamins, over- the-counter remedies, herbs, nutrition supplements and other alternative treatments also affect warfarin, and should not be taken while you are on warfarin.
Are there risks to taking a blood-thinner?
Yes, and the obvious risk is bleeding. By thinning blood, we increase the risk of bleeding (something that can be managed), and decrease the risk of clot formation (which can be lethal). Thus, there is a trade-off in risks. The risk of bleeding is common to all blood thinners.
Drugs sometimes used instead of warfarin include heparin and aspirin. Aspirin is more convenient and does not need monitoring, but is not quite as effective as warfarin. Some people may not be able to take war-farin; in that case we usually use a drug called enoxa-parin. After about 10 days of warfarin, or enoxaparin, we can switch patients to twice-daily aspirin; this com-bination is safe.
Side effects of warfarin and enoxaparin include dizzi-ness, headache, weakness, cuts from shaving/injury that do not stop bleeding, nosebleeds, bleeding of the gums when brushing your teeth, vomiting blood, bruising or skin rashes, dark brown urine, red or black color to stools, unexpected vaginal bleeding, or unusu-al pain or swelling. If any such symptoms appear, we may have to switch to a different blood-thinner.
Warfarin interacts with many drugs, both prescrip-tion and over-the-counter. Special caution should be given to anti-inflammatory medications such as aspi-rin, ibuprofen-containing drugs; naproxen, ketoprofen, cimetidine, ranitidine; and food supplements that con-tain vitamin K.
Supplements, such as ginkgo biloba and danshen also interact with warfarin. Some herbal teas have tonka beans, melilot (sweet clover), or sweet woodruff in them, which contain vitamin K. In addition, foods con-taining fat substitutes such as olestra are supplement-ed with vitamin K. Because so many dietary items affect warfarin, it is es-sential to monitor the action of this drug two or three times every week with blood draws that are done by the home health agency while you recover at home.