Low-Molecular Weight Heparin Best to Prevent Thromboembolism After Spine Surgery

A major concern after any type of major surgery, particularly orthopedic (bone) surgery, is development of blood clots. Called venous thromboembolisms, they can cause severe health problems and even death. These clots can result in deep vein thrombosis (DVT) and pulmonary embolism. A deep vein thrombosis is a clot that forms in a vein deep in the body, well below the skin surface. Although they can happen anywhere, deep vein thrombosis is usually found in the lower leg or thigh. The danger of such a clot is that it can break away from the vein and travel in the blood stream. Once it has broken away, it's called an embolus. The embolus can travel to the lungs and cause a pulmonary embolism.

When someone is awake and moving about, the muscles in their legs help push the blood around and promote blood circulation. When a patient is lying on the operating table, the blood is not being encouraged to move about and this is made worse when the patient lies in bed recuperating from the surgery. The blood circulation in the legs can be sluggish and the blood may begin to clot. Also, surgery often involves positioning and pulling back on the veins to reach the areas to be worked on and this increases the likelihood of a blood clot forming.

According to the authors of this article, each year in the United States, deep vein thrombosis occurs in 48 out of every 100,000 patients and two are fatal, causing death. Pulmonary embolism occurs in 69 out of every 100,000, causing death in 17. Not only do these blood clots affect the patients, they have an economic cost in terms of lost productivity, health care costs, and increased risk of the patients having a second thrombosis or embolus. Because of the large impact, many researchers have conducted studies to try to find ways to minimize the risk of developing a blood clot after surgery. The researchers have looked at using anticoagulants (blood thinners) prophylactically (to prevent) blood clots. These include medications such as low-molecular weight heparin and low-dose heparin. Researchers have also looked at devices such as compression sleeves, that promote blood circulation in the legs. Unfortunately, this type of treatment has complications that can be serious, such as bleeding or hemorrhaging from the surgical wound and blood building up in the spinal area, causing nerve damage.

Venous thromboembolism is a problem that doctors recognized as early as the mid-1800s, but it was only in the mid-1900s that it was really written about in the medical literature. Doctors were able to identify some patients who were at higher risk of developing the blood clots, including people with abnormalities in their blood clotting ability, such as antithrombin deficiency. There are other health problems that may affect blood clotting, such as cancer and treatments, such as hormone replacement therapy.

In 1966, a researcher, Prothero, and colleagues, reported on 1000 patients who had undergone lower back (lumbar) surgery without any prophylactic treatment for blood clots. In the first group of 500, 4.2 percent of the patients developed a blood clot. Ten years later, the second group of 500 patients who had undergone the same type of surgery had a rate of 2.2 percent. Another study that examined the use of compression to prevent blood clots. The researcher, Epstein, found that 2.8 percent of the patients who had back surgery developed clots.

Not all surgeons use medications to try to prevent blood clots when they perform elective back surgery. Their reluctance includes the worry of prolonged bleeding during and after surgery, and a build up of blood in the epidural space. These concerns were examined in a study of almost 2000 patients who had elective back surgery. The researcher, Gerlach and colleagues, found that there was a 0.05 percent risk of venous thromboembolism and a 0 percent risk of pulmonary embolism if the patients wore compression stockings after surgery and were given a dose of low-molecular weight heparin within 24 hours after having had surgery. There were some complications, however. A build up of blood (hematoma) in the epidural space occurred in 0.4 percent of the patients. Of those patients, 77 percent experienced a neurological deficit, or problems with the nerves.

Warfarin, a different type of anticoagulant that patients take in a pill form, hasn't been studied very much for this type of use. One study of 110 patients included 35 patients who were given warfarin and used elastic stockings after back surgery. The researchers didn't find any blood clots, but two of the 35 patients did experience heavy bleeding after surgery.

One important issue in preventing blood clots is to be able to identify patients who may be at greater risk of developing them. Some risk factors that have been identified include having had a blood clot before, not being able to move about after surgery, increased age, and a long surgery. Surgeons have also noticed that how they approach the spine for surgery makes a difference in blood clot risk.

Blood clots are not limited to patients who had elective surgery. A study done of 101 patients who had been injured found a 30 percent rate of blood clots, but there wasn't a difference found between patients who were receiving prophylactic anticoagulants and those who weren't. The did find a higher rate among patients who were obese or over 40 years old, and in those who couldn't move about for more than three days or who had broken their back or bones below the waist. The authors of that study suggested that traumatic injury increases the rate of blood clot formation that could last up to a month after the accident. However, in another study, 45,000 patients who had been injured one year earlier were found to only have a 0.36 percent risk of developing a blood clot.

After a spinal cord injury, blood clots are very common. Up to 80 percent of patients with traumatic spinal cord injury develop a thrombosis if they haven't had prophylactic anticoagulation or if mechanical means (stockings, pressure) haven't been used. When pressure was used, the rates dropped to about 40 percent, according to one researcher, Green and colleagues. Heparin, both low-dose and low-molecular weight, dropped the incidence as well. Interestingly, in one study of 119 patients with spinal injuries, those who underwent six weeks of rehabilitation had a 2.5 percent higher risk of developing blood clots if they were given low-dose heparin than if they received low-molecular weight heparin.

Patients with spinal cord injuries at a higher risk for blood clots overall, with paraplegia (paralysis from the waist down) having a higher rate than quadriplegia (from the chest down). Jones and colleagues found in one study that 11 percent of patients who were complete paraplegics developed blood clots compared with 7.8 percent who were complete quadriplegics. Of course, being older is also a risk,

Overall, the American College of Chest Physicians have recommended that surgeons not prescribe prophylactic anticoagulants to patients who do not have any risk factors for blood clots and who are about to undergo elective spinal surgery. If, however, there are any risk factors, the College recommends that patients be given low-molecular weight heparin and use pressure after surgery to reduce this risk. The heparin should begin within 24 hours of the surgery, but the patients must be watched closely for any signs of a hematoma. The College also recommends this approach for patients who have a fracture or dislocation of the spine and those who had traumatic injury to the spine. How long the heparin is used depends on the doctor and the extent of the patients' injuries or the type of surgery and risk factors, but the generally accepted time is three to four months, which is how long it can take for most blood clots to form.

Another way to deal with patients who are at a particularly high risk of developing blood clots is by using inferior vena cava filters, a filter that is implanted into the large vein (vena cava) that carries blood back from the lower body to the heart. The blood is then filtered to prevent clots from entering the heart.

If a patient does develop a blood clot, treatment can be challenging since doctors don't all agree with the best type of treatment.

The authors of this article concluded that one of the reasons it is difficult to prevent venous thromboembolism is the differences between the patients who are having spinal surgery and the different options available to the surgeons. There has been a drop in blood clots because of early treatment, heparin, and mechanical methods, such as pressure stockings. Therefore, there is enough evidence to show that prophylactic treatment does help reduce the risk of blood clots after spinal surgery. That being said, it has also been shown that low-weight-molecular heparin is the best choice, along with outside pressure, for most patients. The authors do point out that there are complications that may be associated with the treatments, but that risk versus benefit must be taken into account. If a hematoma in the epidural area does form, then immediate surgery is the best response and provides the best long-term outcome for the patient.

Christopher A. Heck, MD, Christopher R. Brown, MD, and William J. Richardson, MD. Venous Thromboembolism in Spine Surgery. In Journal of the American Academy of Orthopaedic Surgeons. November 2008. Vol. 16. No. 11. Pp. 656-664.

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