Fear factor: DVT and the hospitalized medical patient
From the June ACP Observer, copyright © 2005 by the American College of Physicians.
By Deborah Gesensway
SAN FRANCISCO—Virtually all internists at some point in their careers have dealt with the tragedy of watching a seemingly healthy patient drop dead from an unexpected pulmonary embolism (PE).
Deep vein thrombosis (DVT) and the PE that can follow are much more prevalent among non-surgical hospitalized patients than previously believed, said Timothy A. Morris, ACP Member, associate professor of pulmonary and critical care medicine at the University of California, San Diego. "It happens a lot—and a lot more than we think."
As many as 11% of patients who die in the hospital have suffered PE, as do 10% of emergency room patients who can't be revived by emergency medical technicians, Dr. Morris reported. A study in the July 26, 1995, issue of Journal of the American Medical Association (JAMA) found that one-third of patients in one hospital's medical intensive care unit had a DVT as seen by ultrasound.
Timothy A. Morris, ACP Member, says that risk factors for DVT in medical patients include lengthy hospital stays and the use of central venous catheters.
The study concluded that traditionally recognized risk factors failed to identify which hospitalized patients would develop DVT. And autopsy results show that for most cases of fatal PE in which autopsies were performed, physicians missed the diagnosis, Dr. Morris added.
He suggested that one way internists can improve their hospitalized patients' odds of not suffering a fatal PE is "to have a lower threshold for suspicion." In particular, respiratory or hemodynamic compromise, out of proportion to the degree of preexisting pulmonary disease, should trigger a suspicion for PE. However, because "so many [of potentially deadly clots] present in advanced stages after being asymptomatic, prevention is key," Dr. Morris told internists attending an Annual Session course on how to diagnose, treat and prevent DVT and PE.
With surgical patients, the knowledge about risk factors is better. Patients with the greatest chance of developing a clot are those who undergo hip or knee surgery or who have had a previous DVT.
"But with medicine patients, it's not as easy to categorize," he said. For example, 70% of patients with DVT reported in the JAMA study were found to be positive on their first screening test, while nearly half had been in the hospital for at least five days—and two-thirds had received no DVT prophylaxis during their stay. Upper extremity clots, which occurred in 15% of patients, were associated with central venous catheters.
By considering such risk factors, physicians will be more likely to order at least one of the extremely safe types of mechanical venous compression prophylaxis, which are known to cut in half the risk of PE. No one has studied whether the custom-made anti-embolism stockings are more effective than the intermittent pneumatic calf compression, he said.
All of the available drugs—from heparin to fondaparinux, a synthetic pentasaccharide—reduce the risk of blood clots, but they also increase bleeding risk. In Dr. Morris' view, both unfractionated heparin and low molecular weight heparin are the best choices.
"There really is evidence that low-dose heparin works in medical patients," he said. Higher quality studies have been done recently using low molecular weight heparins, both dalteparin and enoxaparin, that showed they are effective prophylactic agents as well. Downsides of low molecular weight heparins are that they are expensive and are renally cleared, so may accumulate in renal impairment.
But another expert speaking about anticoagulation therapy at Annual Session had a different view of available antithrombotic agents. Victor J. Marder, FACP, professor of hematology and medical oncology at the David Geffen School of Medicine at the University of California, Los Angeles, said problems with heparin include not being able to predict a patient's response to the dose. Heparin also might cause heparin-induced thrombocytopenia (HIT).
"HIT is not a common disease," he said, "but it's common in the courtroom."
When it comes to HIT, Dr. Marder said the direct antithrombin agents have some benefits, especially for patients with a thrombotic complication of HIT. The agents are also more effective than heparin or low molecular weight heparin for treating active thrombosis, as they can neutralize clot-bound thrombin.
Fondaparinux, the new anti-factor Xa agent, may also be more effective than low molecular weight heparins and can be given once daily for effective prophylaxis or for treating existing DVT, he said.
A role for CT?
According to Dr. Morris, many physicians are now using CT scans to improve their ability to diagnose DVT in unstable patients and make better decisions about antithrombotic therapy. But he does not believe that CTs' "popularity mirrors how good they have proven to be," particularly compared with pulmonary angiograms.
CT scans can pick up clots in segmental or larger arteries, which account for more than 70% of PEs, he said. But "they are not so great in sub-segmental arteries," he said.
"You can't write off people with smaller clots," he added. "CT is a great tool, but it must be used with a high level of expertise."
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.
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