Author Credentials and Financial Disclosure: Dr. Lovato is an Assistant Clinical Professor at the UCLA School of Medicine, the Director of Critical Care for the Department of Emergency Medicine at Olive View-UCLA Medical Center, and the LLSA Workshop Co-Director for the Olive-View-UCLA National Conference on Advances in Emergency Medicine.
All faculty and staff in a position to control the content of this CME activity have disclosed that they have no financial relationships with, or financial interests in, any commercial companies pertaining to this educational activity.
Learning Objectives: After reading this article, the physician should be able to:
- Describe the risk factors associated with developing deep-vein thrombosis (DVT) and the limitations of compression ultrasonography as a diagnostic test.
- Summarize the initial management strategy of a patient diagnosed with a DVT.
- Explain the important historical elements and clinical signs in patients with acute infectious diarrhea that help guide workup and therapy.
Release Date: April 2008
Treatment of Deep-Vein Thrombosis
Bates SM, Ginsberg JS
N Engl J Med
The German physician Rudolf Ludwig Karl Virchow coined the term “embolia,” and first described the pathophysiology of thromboembolic disease in 1859. Although many clinical factors are thought to independently increase the chance of developing deep-vein thrombosis (DVT), Virchow's triad refers to three overall risk categories: vessel wall damage, venous stasis, and hypercoagulability. With an annual incidence of almost one percent in those over 60, DVT can have lethal consequences, especially when the diagnosis is delayed.
Although venography is considered the gold standard diagnostic test for DVT, compression ultrasonography has the advantage of being less expensive, less invasive, and widely available. In the right hands, sensitivity and specificity of compression ultrasonography is reportedly greater than 95% for detecting proximal DVTs. A significant limitation of compression ultrasonography is that it is unreliable in detecting isolated DVTs at the level of the calf or below. Fortunately, serious emboli are usually not associated with isolated distal thrombosis. Because up to 25 percent of untreated calf thrombi are thought to progress to the proximal veins, however, serial ultrasonography is recommended within one week if the initial ultrasound is negative.
Once DVT is diagnosed, anticoagulation is usually indicated in the form of either unfractionated heparin or low-molecular-weight heparin followed by long-term oral anticoagulation therapy with warfarin. Because unfractionated heparin has relatively unpredictable effects despite standardized, weight-based protocols for intravenous administration, frequent monitoring of partial thromboplastin time (PTT) is necessary, and dosing adjustments are often required. As with all therapies, benefits of heparin anticoagulation should outweigh potential risks of treatment, most notably bleeding and heparin-induced thrombocytopenia.
Low-molecular-weight heparins have been shown to be equally effective for preventing recurrent thromboembolic disease. In contrast to unfractionated heparin, however, low-molecular-weight heparins have better bioavailability and more reproducible protein binding, allowing subcutaneous administration and less laboratory monitoring. Another advantage of low-molecular-weight heparins is the potential to avoid hospital admission in the right clinical setting. Patients with newly diagnosed DVT and low-risk features (e.g., small clot burden, minimal symptoms, no major co-morbidities, no concomitant bleeding risk) who can self-administer medications and who have close follow-up may be managed as outpatients.
Long-term therapy with warfarin titrated to achieve an international normalized ratio (INR) of 2.0 to 3.0, reduces the risk of DVT recurrence by 90 percent. Because the anticoagulant effect of warfarin is often delayed three to four days and not always predictable, patients are often treated with unfractionated or low-molecular-weight heparin until the INR is confirmed to be therapeutic. In cancer patients, warfarin is less effective at preventing recurrent thromboembolism, so long-term therapy with a low-molecular-weight heparin should be considered. Inferior vena cava filter placement prevents pulmonary embolism over the short term in patients with a lower extremity DVT and a contraindication to anticoagulation, but it does not appear to be an effective long-term solution when used without anticoagulation.
Duration of warfarin therapy is usually determined by a primary care provider or another consultant, but it is helpful for the emergency physician to know what factors play a role in making this decision. The bottom line is that warfarin should be discontinued when the risk of major hemorrhage (3% annually) begins to outweigh the risk of recurrent thromboembolic disease. Patients who suffered their first DVT while having a major transient risk factor (e.g., recent surgery, major medical illness, leg casting) are generally treated for only three months if the transient risk factor has resolved.
Treatment is usually extended to six months if only minor risk factors (e.g., OCPs, HRT) were present at the time of DVT diagnosis because these risk factors are less likely to be solely responsible for the event. Idiopathic DVTs (i.e., those with no identified risk factors) are often treated for six months, but recommended treatment may be indefinite in patients with recurrent events, uncontrolled risk factors such as cancer, or if high-risk thrombophilias (e.g., protein C&S deficiencies) are present.
Acute Infectious Diarrhea
Thielman NM, Guerrant RL
N Engl J Med
Diarrhea is defined as increased frequency of defecation, either three or more episodes per day or a total daily stool production of greater than 200 grams. Most emergency physicians prefer the former definition because it is easier to measure. Diarrhea is considered acute if the illness has lasted less than 14 days. This review article focuses mainly on acute infectious diarrhea in immunocompetent adults in industrialized countries.
The initial evaluation of a patient with diarrhea should focus on the severity of illness as well as clinical clues to the underlying etiology. Considering that many episodes of diarrhea are of self-limited viral etiology and that almost 50 percent of all acute diarrhea resolves in less than 24 hours, patients with mild symptoms presenting in the first 24 hours are usually managed without microbiologic investigation. On the other hand, patients with bloody diarrhea, fever, or signs of systemic illness should routinely have a stool sample sent for culture and analysis.
The patient's exposure history and associated clinical signs are often indicative of the underlying etiology of acute infectious diarrhea, and often guide initial testing and management strategies. Acute bloody diarrhea (especially without fever) or associated with hemolytic uremia syndrome (i.e., microangiopathic hemolytic anemia, thrombocytopenia, and renal failure) should prompt specific fecal testing for E. coli O157:H7 and Shiga toxin production. Patients with recent history of shellfish ingestion often have Vibrio species as the causative organism. Clostridium difficile, the most commonly identified etiology of nosocomial diarrhea, should be suspected and ruled out when diarrhea is associated with recent antibiotic use, chemotherapy, or hospitalization.
Protozoal infections such as Giardia and Cryptosporidium should be considered in hikers and patients exposed to untreated water, especially when diarrhea persists for more than seven days. Finally, advanced HIV patients, with acute diarrhea should be evaluated for opportunistic infections such as Cryptosporidium, microsporidia, Cyclospora, Isospora, Mycobacterium avium complex, and cytomegalovirus. Because the diagnostic yield of stool cultures is less than five percent and laboratory test availability varies with institution, the laboratory should be notified when a specific organism is suspected to ensure that specimens are appropriately processed.
The initial focus of therapy for the dehydrated patient is fluid resuscitation regardless of the underlying etiology. In patients with frequent defecation, tenesmus, or crampy abdominal pain, loperamide is the oral antimotility agent of choice and has been shown to reduce symptoms by as much as one day. Antimicrobial therapy for diarrhea in general is most effective with early treatment, and also may reduce the risk of transmission. The choice of antibiotic is often empiric pending laboratory testing.
For community-acquired diarrhea in adults, a fluoroquinolone is the agent of choice. A macrolide is a good alternative in areas with strains of fluoroquinolone-resistant campylobacter. Studies suggesting an association between E. coli O157:H7-induced diarrhea treated with antibiotics and the hemolytic uremia syndrome are the source of many physician's concerns over empiric antibiotic treatment (especially in children), but the relevance of this association remains controversial.
Traveler's diarrhea is usually self-limited, but quinolones have been shown to reduce symptoms by one or two days. Although antibiotic prophylaxis is not recommended for travelers even in high-risk areas, bismuth subsalicylate used four times a day can significantly decrease the incidence of traveler's diarrhea. Nosocomial diarrhea caused by Clostridium difficile responds well to discontinuation of broad spectrum antibiotics and oral treatment with metronidazole. Giardia is a commonly implicated protozoal infection in acute diarrhea lasting more than seven days and also responds well to oral metronidazole.
About the LLSA
As part of its continuous certification program, the American Board of Emergency Medicine has developed the Lifelong Learning and Self-Assessment (LLSA) program to promote continuous education of diplomates. Each year, beginning in 2004, 16 to 20 articles are chosen based on the Emergency Medicine Model. A list of these articles can be found on the ABEM web site, www.abem.org.
ABEM is not authorized to confer CME credit for the successful completion of the LLSA test, but it has no objection to physicians participating in such activities. EMN's CME activity, Learning to Live with the LLSA, is not affiliated with ABEM's LLSA program, and reading this article and completing the quiz does not count toward ABEM certification. Rather, participants may earn 1 CME credit from the Lippincott Continuing Medical Education Institute, Inc., for each completed EMN quiz.