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Weighing the risks of anticoagulant bridging after surgery

From the July-August ACP Observer, copyright 2006 by the American College of Physicians.

By Deborah Gesensway

WASHINGTON—When deciding how to manage surgical patients on oral anticoagulants, many physicians weigh patients' risk of post-op bleeding against that of a stroke or transient ischemic attack (TIA)—and take their chances with bleeding. They'll administer an anticoagulation bridging regimen, such as subcutaneous low-molecular-weight heparin (LMWH) or intravenous heparin.

But could aggressive perioperative bridging increase the risk of both post-op bleeds and of a catastrophic thromboembolic event for patients on warfarin? Two experts argued those questions at a perioperative medicine session at the Society of Hospital Medicine’s spring meeting. At the heart of the debate was how to interpret the scant—but growing—data on whether to offer pre- and post-operative bridging therapy.

Both doctors agreed that there is growing consensus at the extremes of bleeding and thromboembolic risk. Patients at low stroke risk likely do not need bridging anticoagulation, while those at high stroke risk, such as those with mechanical mitral valves, need a more aggressive approach.

And both agreed that the bleeding risk from bridging anticoagulation is low for invasive procedures. However, controversy exists for patients at intermediate risk for stroke who are on long-term warfarin and undergoing major surgery. The minimalist tack suggests avoiding therapy with unfractionated heparin (UFH) or LMWH due to increased risk of bleeding, while the aggressive approach involves bridging to decrease stroke risk.

The minimalist approach

Doctors are taking too many chances with bleeding, according to one side of the debate, represented by Andrew S. Dunn, FACP, medical director of general internal medicine at Mount Sinai Medical Center in New York and director of its anticoagulation service.

Bleeding is not uncommon after major surgery if bridging anticoagulation is administered, he said, and patients who bleed while on perioperative UFH or LMWH will typically have their anticoagulation therapy stopped to stem the bleeding. That puts them at greater risk of suffering a thromboembolism for a longer period of time than if no bridging regimen had been chosen.

The consequences of both thromboembolism and major bleeding are serious, he pointed out. Between 5% and 10% of recurrent venous thromboemboli (TE) are fatal—while about 30% of thromboembolic strokes are fatal and over 40% result in permanent disability. But major post-op bleeding is dangerous too: Between 3% and 13% of major bleeding events are fatal.

Dr. Dunn explained his reasoning this way: Some feel the risk of post-operative stroke is as low as 0.2%. But even if you believe these patients' risk is as much as 1% and if you can reduce that risk three-quarters by anticoagulation, then you need to treat 133 patients to prevent one stroke or TIA.

“You may say 'I can accept that number,' because stroke or TIA is usually catastrophic,” he said. But “if major bleeding after major surgery is increased by 10%, which is a reasonable estimate, you are going to cause 13 major bleeds."

And how about patients on anticoagulants who are having a major bleed? "You stop the anticoagulants, and now you are exposing these 13 patients to a longer period without anticoagulation. That could cause some TE events after you induce some bleeding.”

Instead, he said, physicians should be selective about which patients need bridging, depending on patient characteristics and the kinds of surgery most likely to result in post-op bleeds.

The aggressive view

Amir K. Jaffer, ACP Member, associate professor of medicine at the Cleveland Clinic Lerner College of Medicine of Case Western University and associate section head for hospital medicine at the Cleveland Clinic Foundation in Cleveland, urged a different approach. Dr. Jaffer directs the clinic’s IMPACT (Internal Medicine Preoperative Assessment Consultation and Treatment) Center and its anticoagulation clinic.

According to Dr. Jaffer, the minimalist strategy is supported by a mathematical calculation that suggests the perioperative thromboembolism rate is 0.2%. He feels this rate is between five and 10 times lower than what is seen in real practice.

The 1%-2% perioperative arterial thromboembolism rate around the time of surgery seen in real life suggests a phenomenon of perioperative hypercoagulability. According to Dr. Jaffer, the surgical milieu can induce a hypercoagulable state in many patients—and the risk of venous TE increases 100-fold during the perioperative period, although the impact on arterial events is unknown.

That increased risk may be due both to the fact that warfarin is abruptly stopped and to the surgery itself. “Therefore, the risk perioperatively is a lot higher than you would get if you did this simple mathematical calculation,” he said.

“A minimalistic strategy is what is favored if there is no hypercoagulable state," he concluded. "But clearly, the numbers support that there is a hypercoagulable state—and if there is, an aggressive strategy is favored."

Finding an answer

Fortunately, there is middle ground. Both physicians agreed that the key to perioperative bridging is to personalize every decision, based on everything from the type of surgery and specific clotting problems to the reason the patient is on warfarin in the first place.

“Is it for atrial fibrillation or for a mechanical valve—and what kind of mechanical valve?” Dr. Jaffer asked. “You need to quantify in your own mind what the risk of thrombosis for that patient is.”

In addition, he said, using prophylactic—not full doses—of heparin or LMWH may reduce the chance of bleeding immediately post-op, but the use of prophylactic doses and then escalation to full dose LMWH has not been proven in a randomized clinical trial.

And both agreed that more research is urgently needed. “This is really a common clinical dilemma," said Dr. Jaffer, "that is too important to say, 'there is no answer.'”

Deborah Gesensway is a freelance health care writer in Toronto.

The information included herein should never be used as a substitute for clinical judgment and does not represent an official position of ACP.


Tips for understanding, overcoming perioperative challenges

WASHINGTON—Anticoagulation wasn't the only topic of discussion at a course on perioperative medicine during the Society of Hospital Medicine's annual meeting. Experts explored the latest thinking on major perioperative challenges, including:

Post-op pulmonary complications

In patients about to undergo noncardiothoracic surgery, assessing their risk of post-op pulmonary complications typically takes a backseat to cardiac evaluation, said Ahsan M. Arozullah, MD, MPH, assistant professor of medicine and health promotion research at the University of Illinois at Chicago and staff physician at the Jesse Brown VA Medical Center in Chicago.

However, in light of new ACP guidelines and recently published studies, physicians can no longer ignore the possibility of post-op pulmonary complications, Dr. Arozullah said.

Pneumonia and respiratory failure are two common post-op complications, with nearly one-quarter of all deaths that occur within six days of surgery related to post-op pulmonary complications.

Conditions that make surgery risky in terms of pulmonary complications, he said, are the patient’s functional status, low albumin levels and how close the surgical site is to the patient’s diaphragm. Physicians can now use a point-based risk index to assess risk, using information gleaned from a history, physical and two lab tests—a blood urea nitrogen and albumin.

Evidence shows, he added, that “any kind of breathing helps” to reduce the chance of complications. All breathing incentive systems, from incentive spirometry to deep breathing exercises, are effective.

Bariatric surgery

With the number of bariatric operations sharply on the rise, physicians face real challenges in preparing patients medically for surgery.

Cardiac risk evaluation is particularly difficult with morbidly obese patients, said David V. Gugliotti, ACP Member, a hospitalist at Cleveland Clinic in Cleveland. Exercise stress tests tend to have too many false positives in obese women, while SPECT imaging can be less accurate in patients with a body mass index of more than 30.

PET scans, on the other hand, tend to have greater specificity. However, stress echocardiography is the preferred test, and dobutomine stress echos have been shown to be safe in obese patients, he said.

According to Bipan Chand, MD, Cleveland Clinic's director of surgical endoscopy, the most common and worrisome complication of bariatric surgery—even though it occurs less than 5% of the time—is a gastrointestinal leak. Internists should keep in mind that leaks most commonly show up as tachycardia, and are most likely to occur between five and seven days after the operation.

The other major complication is deep venous thrombosis (DVT). Pulmonary embolism is the most commonly reported cause of mortality in the first month following surgery, Dr. Gugliotti said.

As a result, physicians should order mechanical DVT prophylaxis for all patients undergoing bariatric surgery. These patients should also receive pharmacologic prophylaxis, as some evidence indicates that higher doses of low molecular weight heparin are required for morbidly obese patients. Many gastric bypass patients at the highest risk of developing DVT, he said, should be given enoxaparin for an extended period of time, perhaps up to four weeks following surgery.

Post-op fever

Many patients will have a fever post-op and develop an infection. But the two aren’t always the same, said James C. Pile, FACP, a hospitalist and co-director of perioperative services at Case Western Reserve University/MetroHealth Medical Center in Cleveland. Here were his tips for evaluating fevers post-op:

  • Look for clues. Fevers on the first day after surgery, he said, are "usually benign." Physicians should refrain from ordering additional lab tests right away. Instead, they should perform a careful history and exam, examining the operative note and nursing notes for additional clues.
  • Recognize when it's an infection. A fever that appears after the first few days is increasingly likely to indicate an infection. Common ones include urinary tract infections, surgical site infections, pneumonia, IV catheter-related infections and C. difficile diarrhea.
  • Look for other causes of non-infectious fever. Other common causes of non-infectious post-op fever include drug fever, hematoma, gout, transfusion reaction, pulmonary embolism, pancreatitis and alcohol withdrawal. Contrary to what nearly all physicians were taught, said Dr. Pile, atelectasis does not cause fever.
  • Beware of early, dangerous fevers. Physicians must also watch for the few, very dangerous “can’t miss” causes of early post-op fever. Those include myonecrosis, bowel leak, adrenal insufficiency and malignant hyperthermia.

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