Why Heparin Is Used After Surgery

Heparin After Surgery

Heparin is an anticoagulant commonly used after surgery. It is used to prevent the blood from clotting too easily while the patient is spending more time resting and off of their feet than usual—which is when blood clots are more likely to form.

Masked physicians working on a patient
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Heparin is also used to treat blood clots when they do form, helping prevent the clot from increasing in size and preventing additional clots from occurring. Surgery is a known risk factor for the formation of clots. The risk of blood clots increases significantly during the early stages of recovery, so it is common for surgery patients to receive routine doses of heparin while in the hospital.

Heparin is considered an important preventive measure during an inpatient stay after a procedure. It is often stopped when the patient is discharged from the hospital.

Uses After Surgery

Heparin is often given after surgery, particularly in patients who will remain hospitalized for several days after surgery, to prevent blood clots from forming. Patients who are unable to get out of bed in the days following surgery are at greater risk of forming clots, making heparin a commonly used drug in intensive care units.

For these patients, heparin is often given every few hours around the clock, in an effort to reduce the risk of a life-threatening pulmonary embolism, or clot. Kidney function will often determine how often heparin can safely be given to prevent clots.

Heparin is given subcutaneously, meaning it is injected into the body in an area such as the abdomen, and can also be given intravenously (IV, through a vein). There is no oral form of heparin, but some other blood thinners can be given in a tablet form.

Lovenox, which is low molecular weight heparin, is also frequently used after surgery and is used instead of heparin, not with heparin. Lovenox is given as an injection.

Dosage After Surgery

Heparin dosages vary widely from patient to patient and are dependent upon the use of the medication. Small amounts can be added to IV fluids to keep an IV line flowing freely. Larger amounts may be injected several times a day to prevent clotting.

IV heparin is titrated, or adjusted, according to lab results, so the dose is unique to the patient if it is being given as a drip. The drip is often started based on ideal body weight and then adjusted based on the body’s response to the medication approximately every six hours.

This requires frequent blood draws to check how “thin” the patient’s blood is periodically throughout the day, as overly thin blood can be dangerous and lead to unexpected bleeding.

In children, the injection dosage is based upon weight in kilograms. While the dosages are significantly smaller for most children than adults, they are also individualized to each pediatric patient. If the patient is on a heparin drip, the drip will be adjusted according to lab results in the same way adults would be.


It is not uncommon for bruising to appear around heparin injection sites. But small bruises are considered a normal side effect of administration and are not typical signs of a problem. A patient who spends an extended period of time in the hospital and receiving three heparin injections a day may end up with a belly covered in small bruises in varying stages of healing.

Too much heparin can cause the blood to become too thin and can result in bleeding. An overdose of heparin, such as giving an infant an adult dose of the drug, can cause bleeding so severe that it can result in death. The most common signs of heparin overdose include nosebleeds, blood in the urine, or blood in the stool.

Heparin-induced thrombocytopenia (HIT) is a rare complication of heparin administration. HIT happens when heparin causes a drastic reduction in the number of platelets, the blood cells that cause clotting.

This can lead to bleeding, but also, the platelets clump together and form clots in arteries, requiring emergency surgery to open them up again. In most cases, stopping the delivery of heparin is an effective treatment.

A Word From Verywell

Heparin is a well-studied medication that has a strong record of preventing blood clots and thrombus—both of which can be life-threatening. Side effects, aside from bleeding more easily, are rare but can be significant when they occur.

For most patients, the reward of using heparin after surgery is far greater than the potential risks, but any concerns should be addressed with the surgeon or member of the team providing care while in the hospital.

Frequently Asked Questions

  • How does heparin work?

    Heparin works by decreasing your blood’s ability to form clots. It can also stop the growth of blood clots, but it can’t shrink blood clots that are already formed.

  • When is heparin stopped before surgery?

    Heparin may be stopped about four to 24 hours before surgery.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Library of Medicine. DailyMed. HEPARIN SODIUM- heparin sodium injection, solution [drug label].

  2. Douketis JD, Spyropoulos AC, Spencer FA, et al. Perioperative management of antithrombotic therapy. Chest. 2012;141(2):e326S-e350S. doi:10.1378/chest.11-2298

  3. National Library of Medicine. DailyMed. LOVENOX- enoxaparin sodium injection [drug label].

  4. Rizk E, Wilson AD, Murillo MU, Putney DR. Comparison of antifactor Xa and activated partial thromboplastin time monitoring for heparin dosing in vascular surgery patients: a single-center retrospective study. Ther Drug Monit. 2018;40(1):151-155. doi:10.1097/FTD.0000000000000463

  5. MedlinePlus. Heparin injection.

  6. Hornor MA, Duane TM, Ehlers AP, et al. American College of Surgeons’ guidelines for the perioperative management of antithrombotic medication. J Am Coll Surg. 2018;227(5):521-536.e1. doi:10.1016/j.jamcollsurg.2018.08.183

By Jennifer Whitlock, RN, MSN, FN
Jennifer Whitlock, RN, MSN, FNP-C, is a board-certified family nurse practitioner. She has experience in primary care and hospital medicine.