September 2016

Reducing postoperative thromboembolism risk

9vascular-shutterstock_4828576Preventing deep venous thrombosis and pulmonary embolism after lower extremity surgery can involve pharmaceutical therapies or mechanical interventions. The type of prophylaxis used depends on the type of surgery, pre-existing risk factors, and patient preference.

By Barbara Boughton

Venous thromboembolic events (VTE)—a category that includes deep vein thrombosis (DVT) and pulmonary embolism (PE)—are some of the most serious complications of lower extremity surgeries, particularly those involving the knee and hip.

Without prophylaxis, the risk of asymptomatic DVT after total hip arthroplasty (THA) ranges from 40% to 60%; after total knee arthroplasty (TKA), the incidence ranges from 40% to 85%.1

Prophylaxis for VTE after surgery ranges from the complex to the simple—from injectable anticoagulants such as low molecular weight heparin to intermittent pneumatic compression devices and foot pumps. Compression sleeves and stockings are also used. The type of VTE prophylaxis often depends on the type of surgery, a patient’s pre-existing risk factors, and sometimes patient and clinician preference.

The good news is that the push to reduce VTE has led to more diligence around VTE prophylaxis.

“Over the past four to five years, more patients are receiving prophylaxis after lower extremity surgeries such as TKA and THA. And there’s an increased emphasis on assessing patients’ risk factors and choosing the right treatment for individual patients—and documenting the reasons for these choices,” said Darryl Kaelin, MD, associate professor of physical medicine and rehabilitation at the University of Louisville in Kentucky and current vice president of the American Academy of Physical Medicine and Rehabilitation.

Risk stratification protocols are currently under study, and have been shown to be effective for choosing the right method of VTE prophylaxis for individual patients.

While medications often play a central role in prophylaxis after THA and TKA, early weight-bearing and mechanical methods can play a crucial role too. A patient’s pre-existing risk factors for either VTE or bleeding events are likely to be major considerations. Absent any pre-existing risk factors, however, the choice of VTE prevention can also be driven partly by patient preference.

Risk assessment

An important first step in prescribing VTE prophylaxis is to accurately and thoroughly assess a patient’s risk for VTE as well as bleeding events. Risk stratification protocols are currently under study, and have proven to be an effective means of choosing the right protocol for individual patients. In one study of a risk stratification protocol,2 for instance, 3143 patients undergoing total joint arthro­plasties were classified as having either “routine” or “high” risk for VTE. Patients classified as having routine risk (70.7% of patients) received mobile compression devices for 10 days and aspirin twice daily for six weeks. High-risk patients (29.3%) took warfarin for four weeks and wore compression stockings for six weeks.

Results indicated that the rate of symptomatic VTE in the routine-risk versus the high-risk cohort six weeks postoperatively was .7% compared with .5%. The rate of major bleeding events, understandably, was significantly lower in the routine-risk group (.4%) versus high-risk patients (2%).

“The use of a risk stratification protocol allowed the avoidance of more aggressive anticoagulation in 70% of patients while achieving a low overall incidence of symptomatic VTE,” the authors of the study concluded.

Some of the strongest risk factors for VTE are a personal history of VTE, hypercoagulability, and active or recent cancer.3,4 Other risk factors include obesity, advanced age, diabetes, and varicose veins. Prolonged immobilization is also a strong risk factor for VTE.

Early postoperative mobilization is a tried and true method for increasing blood flow, but how early patients can bear weight depends on the type of procedure.

Clinicians also use the Caprini Deep Vein Thrombosis risk score to predict the clinical incidence of DVT. Validated in clinical trials involving more than 8000 patients,5 it considers age; gender; type and length of surgery (including THA or TKA); pre-existing patient characteristics such as previous heart attack, lung disease, and blood clots; and the time for which the patient will be confined to bed rest. Other risk factors to consider include a history of autoimmune disorder, according to clinicians interviewed by LER.

“You have to look at every patient as having risk if they’re undergoing lower extremity surgery,” said Marlin Schul, MD, MBA, a dedicated deep vein specialist at the Lafayette Regional Vein & Laser Center in Indiana. “Patients who are high risk will need some sort of pharmacologic prophylaxis, while those who have a low or intermediate risk may need at least some combination of compression and early mobilization.”

Mechanical methods

Early mobilization is one of the most tried and true methods for increasing blood flow and preventing blood clots, but how early patients can bear weight depends on the surgery.

“Still, even with total knee or total hip arthroplasties, we try to get patients up the same day or the next day after their surgery. It’s the best way to reduce the risk for developing a blood clot,” Kaelin said.

Guidelines published by the American College of Chest Physicians (ACCP) suggest the use of medications over mechanical methods, but intermittent pneumatic compression (IPC) devices are also valuable in preventing clot formation, according to the guidelines.6 In patients receiving pharmacologic prophylaxis after major orthopedic surgery, the ACCP guidelines also suggest using an IPC device during the hospital stay. Patients at increased bleeding risk should also use an IPC device after they leave the hospital for 10 days to a month, according to the ACCP guidelines.

Guidelines from the American Academy of Orthopaedic Surgeons (AAOS) also note that patients who are undergoing elective TKA or THA and have had a previous VTE should receive both pharma­cologic prophylaxis and mechanical compressive devices.7

Many surgeons also apply a compression pump or device during surgery—but on the opposite limb from that undergoing surgery.

“It prevents the blood from pooling, and helps pump blood back toward the heart. Using these mechanical devices during surgery also allows the soft tissue to release plasma thromboplastin factors that reduce the risk for clotting,” said Louis Kwong, MD, professor of orthopaedic surgery at the David Geffen School of Medicine at UCLA and chair and medical director of the Orthopaedic Clinics at the Harbor-UCLA Medical Center in Los Angeles.

Once outside the hospital, some patients also do well with a mechanical compressive device or foot pump, Kwong said.

“A number of studies demonstrate the clear effectiveness of mechanical methods, but patient compliance can be an issue after the patient returns home,” he said. “Some patients are very accepting of the mechanical devices—and even prefer them to medication—but others find them cumbersome and uncomfortable, especially in hot and humid weather.”

If the patient is not weightbearing, an IPC device or foot pump has to be worn for 18 to 22 hours a day for at least two weeks, and that can be an onerous task for some patients—especially since the devices have to be plugged into the wall, which limits mobility. Some IPC devices can be carried in a pouch with the patient, but lugging the device everywhere one goes is seen as a major inconvenience by some patients, Kwong said.

“If compliance starts to fall off, either because the patient does not wear the device or doesn’t wear it for the required number of hours, then the patient is put at risk for a DVT,” he emphasized.

Still, for patients who are immobile and need to use a mechanical device to prevent DVT, an IPC device can be the method of choice if a compression stocking or sleeve cannot fit over the foot and ankle after surgery, Schul notes. More convenient stockings and sleeves can sometimes be applied before surgery and can be left on afterward—but that’s not always the case, he added.

An IPC device can be hooked up in the recovery room by either the surgeon or the nurse.

“It’s important to aim for 100% compliance in the recovery room, because it’s the highest risk time for DVT—by having the doctor or nurse hook up the pump. That’s also an ideal time to reinforce the need for compliance. If it’s not on, an intermittent pneumatic compression won’t do much good,” says John Morris, MD, an orthopedic surgeon and staff physician at St. Joseph Mercy Hospital in Ann Arbor, MI.

The advantage of these devices is that they carry no risk for bleeding, and for some patients—even those at average risk for bleeding events—that can be a relief, Morris said. The cost of these devices, while not always covered by insurance, is also not prohibitive. In Michigan, they can be rented for several hundred dollars for several weeks, he said.

One advantage of mechanical methods such as pneumatic compression devices, as well as compression stockings, is that they can facilitate early mobilization. Because these methods reduce swelling, studies show that patients are more likely to be up and walking earlier in the recovery period.8

Compression stockings

Since compression stockings reduce the risk for postoperative swelling and thus encourage earlier weightbearing, the result may be a decreased risk for DVT. Compression stockings are usually used in combination with other methods—either medication or early mobilization, depending on the patient’s risk factors and surgery. Their benefits include practicality and convenience—if they can be fit over the foot and leg, according to Schul.

At the same time, studies on the efficacy of compression stockings for preventing DVT events have been conflicting. One explanation may be that studies on compression stockings as DVT prophylaxis have been subject to small sample bias and have not adequately controlled for lack of patient compliance, according to at least one review.9

Yet, patient compliance with compression stockings often depends on education and ease of use, research has revealed. A recent study on elastic compression stockings, for instance, found that patients were willing to wear the stockings after DVT to prevent post-thrombotic syndrome (PTS) for an extended time—up to one year—if they were educated about PTS risk reduction and could put on the stockings themselves.10

“These rather simple interventions could improve compliance,” the authors noted.10

Incorrectly sized stockings can also cause proximal indentation, which can interrupt venous return. However, recent research indicates that carefully sizing stockings and measuring the pressures underneath them can significantly reduce the risk for proximal indentation. In one study, such a protocol significantly reduced the incidence of proximal indentation among 57 TKA and THA patients wearing compression stockings, from 53% to 19%.11 The incidence of incorrectly sized stockings also fell significantly, from 74% to 34%.

Foot and ankle surgeries

The question of whether VTE prophylaxis should be used after surgery, and which method is best, is more unsettled with regard to foot and ankle surgeries than THA and TKA. According to guidelines from the American Orthopaedic Foot and Ankle Society, the assessment of patient risk factors for VTE can depend at least partly on the procedure performed.12 And the correlation of patient risk factors with VTE from foot and ankle procedures has not been robustly investigated. Mechanical prophylaxis for foot and ankle procedures can range from elastic compression stockings to foot pumps and IPC devices, but the true efficacy of these modalities for preventing VTE after foot and ankle surgeries is as yet unknown, the guidelines note.

Chemical prophylaxis has also not been investigated thoroughly in the setting of foot and ankle surgeries. Some studies have found that medication-based interventions have negligible effects on preventing thromboembolic events after foot and ankle procedures.13 The ACCP even suggests no prophylaxis rather than pharmacologic preventive methods in low-risk patients with isolated lower leg injuries (or surgical procedures) that require immobilization.

The American College of Foot and Ankle Surgeons’ (ACFAS) Clinical Consensus Statement on preventing VTE after foot and ankle surgery recommends that chemical prophylaxis for VTE after foot and ankle surgeries should not be used routinely.14 Instead, the clinician should consider each patient’s risk for both VTE and for bleeding events that could stem from prophylactic medications, according to the statement.

Patient characteristics and clinical history, as well as the length of immobilization, should be carefully weighed when deciding upon VTE prevention, according to the ACFAS consensus statement. Immobilizations with the most potential for VTE risk are those that last more than four weeks, are rigid, or are coupled with other patient risk factors, the guidelines note.

Despite these guidelines, there is still a lack of clinical consensus about preventing VTE after foot and ankle surgery—particularly for patients without clear risk factors. A recent poster at the 2016 annual meeting of the American Podiatric Medical Association in Philadelphia highlighted the diverging opinions and practices among foot and ankle surgeons for prevention of DVT after surgery.15 In the study, 785 ACFAS members responded to a survey about current practices in DVT prevention and treatment. According to the survey, the most common form of DVT prophylaxis after surgery was low molecular weight heparin, but for 30% of respondents it was a compression device or stockings, and, for nearly a quarter of respondents (23%), it was aspirin alone. There was also wide variation in factors influencing clinician’s decisions about postoperative chemical prophylaxis, but most respondents (78%) said a patient’s history of DVT or PE routinely affected their decisions.

“There really is no scientific consensus about how to treat patients after foot and ankle surgery to prevent DVT—or whether to use any preventive method at all,” said Christopher DiGiovanni, MD, chief of foot and ankle surgery at Massachusetts General Hospital in Boston and at nearby Newton Wellesley Hospital. “As a result, we either overtreat, undertreat, or, if we are lucky, we get it right.”

To address the lack of robust research in this area, DiGiovanni is working to obtain funding for a $12 million international study with 27,000 patients to analyze the effects of no treatment, aspirin, or anticoagulants after foot and ankle surgery. Although mechanical methods are not being studied, the study—if funded—should shed some light on the question of whether medications are useful, he said.

“My preference as an individual clinician is to give patients low-dose aspirin and also get them up and moving as soon as possible after the surgery. Once they are weightbearing, then I prefer to stop the medications,” DiGiovanni said.

The study could also help determine the extent to which a patient’s individual risk factors for DVT and bleeding events should factor into the prophylaxis equation, he said.

“If the study I’m working on gets fully funded, we should be able to stratify patients based on their risk factors to different preventive methods,” DiGiovanni said. “And that will provide some guidance about what type of prevention should be used.”

Barbara Boughton is a freelance writer based in the San Francisco Bay Area.

REFERENCES
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