eMedicine Specialties > Orthopedic Surgery > Systemic Diseases

Thromboembolism

Author: Vera A De Palo, MD, Assistant Professor, Department of Medicine, Brown University School of Medicine; Director, Intensive Care Unit, Associate Chief of Medicine, Memorial Hospital of Rhode Island
Contributor Information and Disclosures

Updated: Dec 10, 2009

Introduction

Background

Thromboembolism encompasses two interrelated conditions that are part of the same spectrum, deep venous thrombosis (DVT) and pulmonary embolism (PE). PE is the obstruction of blood flow to one or more arteries of the lung by a thrombus lodged in a pulmonary vessel, as shown in the image below.

The clinical practice guideline published in 2009 by the AAOS regarding the prevention of pulmonary embolism in patients undergoing total hip replacement (THR) or total knee replacement (TKR) includes the following recommendations^6,7,8,9 :

• Mechanical prophylaxis and early mobilization are recommended for all patients.
• The following statements summarize the recommendations for chemoprophylaxis:
  • Patients at standard risk of both PE and major bleeding should be considered for aspirin, low-molecular-weight heparin (LMWH), synthetic pentasaccharides, or warfarin with an international normalized ratio (INR) goal of less than or equal to 2.0.
  • Patients at elevated (above standard) risk of PE and at standard risk of major bleeding should be considered for LMWH, synthetic pentasaccharides, or warfarin with an INR goal of less than or equal to 2.0.
  • Patients at standard risk of PE and at elevated (above standard) risk of major bleeding should be considered for aspirin, warfarin with an INR goal of less than or equal to 2.0, or none.
  • Patients at elevated (above standard) risk of both PE and major bleeding should be considered for aspirin, warfarin with an INR goal of less than or equal to 2.0, or none.

Recent studies

Markel et al reported on a 2008 survey of American Association of Hip and Knee Surgeons, exploring venous thromboembolism protocols for lower-extremity total joint surgery. More than 70% reported that their primary hospital now mandates prophylaxis for venous thromboembolism. Low-molecular-weight heparin was considered to be the most efficacious, but aspirin was considered the easiest to use with the lowest risks of bleeding and wound drainage. Warfarin was the most used agent in hospital prophylaxis, and 90% of respondents targeted an international normalized ratio of 1.6 to 2.5.¹⁰

Merli et al reviewed clinical studies of oral anticoagulants for venous thromboembolism prevention in orthopedic surgery and compared them with large observational registries. Results from phase II/III studies, according to the authors, suggest that new oral anticoagulants may provide an efficacious alternative in prevention of venous thromboembolism in orthopedic surgery and have had a good overall safety profile, with no evidence of increased hepatotoxicity. Comparison with large observational registries, however, revealed differences between real-life patient populations, and differences in endpoint definitions also prevented indirect comparison of agents. The authors added that specific compliance and postmarketing safety issues (especially liver enzyme monitoring requirements) need to be clarified before these agents can be widely accepted in routine clinical practice.¹¹

Pathophysiology

Hypercoagulability or obstruction leads to the formation of thrombus in the deep veins of the legs, pelvis, or arms. As the clot propagates, proximal extension occurs, which may dislodge or fragment and embolize to the pulmonary arteries. This causes pulmonary artery obstruction, and the release of vasoactive agents (ie, serotonin) by platelets increases pulmonary vascular resistance. The arterial obstruction increases alveolar dead space and leads to redistribution of blood flow, thus impairing gas exchange due to the creation of low ventilation-perfusion areas within the lung.

Stimulation of irritant receptors causes alveolar hyperventilation. Reflex bronchoconstriction occurs and augments airway resistance. Lung edema decreases pulmonary compliance. The increased pulmonary vascular resistance causes an increase in right ventricular afterload, and tension rises in the right ventricular wall, which may lead to dilatation, dysfunction, and ischemia of the right ventricle. Right heart failure can occur and lead to cardiogenic shock and even death. In the presence of a patent foramen ovale or atrial septal defect, paradoxical embolism may occur, as well as right-to-left shunting of blood with severe hypoxemia.

Frequency

United States

Epidemiologic studies of thromboembolism in Massachusetts and Minnesota find the incidence of venous thromboembolism to be about 1 in 1000 per year. Approximately 5 million cases of deep venous thrombosis and about 600,000 cases of pulmonary embolism occur per year.

International

Thromboembolism has a significant impact on morbidity and mortality internationally. A large survey from Sweden documented confirmed deep venous thrombosis in 1.6 in 1000 per year. The Scandinavian literature also documents that 3-4% of patients who died within 3 months of a fractured neck of the femur died of fatal pulmonary embolism.

Mortality/Morbidity

• About one third of PE cases are fatal. Sixty-seven percent of these are not diagnosed premortem, and 34% occur rapidly. A high rate of clinically unsuspected DVT and PE leads to significant diagnostic and therapeutic delays, and this accounts for substantial morbidity and mortality.
• Thromboembolic disease accounts for approximately a quarter of a million hospitalizations in the United States yearly and for about 5-10% of all deaths.

Race

The incidence of thromboembolism is higher in African Americans than it is in whites. Asians have a lower incidence than both African Americans and whites.

Sex

Pulmonary embolism occurs more frequently in men than in women.

Age

Age is a risk factor for thromboembolic disease. The risk of thromboembolic disease is greater in older patients than in younger patients. It doubles with each decade in persons older than 40 years.

Clinical

History

With pulmonary embolism, the patient often experiences acute onset of shortness of breath; sometimes the patient even pinpoints the moment of distress. Complaints related to the signs of deep venous thrombosis, lower extremity swelling and warmth to touch or tenderness, may be present. Dyspnea is the most frequent symptom of pulmonary embolism (PE). With a smaller PE near the pleura, the patient may complain of pleuritic chest pain, cough, or hemoptysis. Sometimes, massive PE can present with syncope. The patient may have a sense of impending doom with apprehension and anxiety. History may reveal the presence of one or more causes or risk factors (see Clinical, Causes, below).

Physical

Tachypnea, a respiratory rate of more than 18 breaths per minute, is the most common sign of pulmonary embolism. Tachycardia often is present. The second heart sound can be accentuated. Fever may be present. Lung examination findings frequently are normal. Cyanosis may be present. Some patients have signs of deep venous thrombosis, lower extremity swelling, and tenderness and warmth to touch.

Causes

• Risk factors for thromboembolic disease can be divided into a number of categories, including patient-related factors, disease states, surgical factors, and hematologic disorders. Risk is additive.
  • Patient-related factors include obesity, varicose veins, use of oral contraceptives or estrogen, and immobility.
  • Disease states such as malignancy, congestive heart failure, nephrotic syndrome, recent myocardial infarction, inflammatory bowel disease, spinal cord injury with paralysis, and pelvic, hip, or long-bone fracture confer increased risk of thromboembolic disease.
  • Surgical factors are related to procedure type and procedure duration. Fifty percent of patients who have undergone hip surgery have a proximal DVT on the same side as the hip surgery. This is thought to be due to a twisting of the femoral vein during total hip replacement. The incidence of DVT is higher in patients who have undergone knee surgery. In a study of patients following pelvic surgery, 40-80% had calf DVT, and 10-20% had thigh vein thromboses. Fatal PE developed in 1-5% of patients. The risk for thromboembolic disease has been shown to be increased with coronary artery bypass grafting, urologic surgery, and neurosurgery.
  • Hematologic disorders that increase thromboembolic risk include activated protein C-resistance (factor V Leiden), protein C or protein S deficiency, antithrombin III deficiency, lupus anticoagulant, polycythemia vera, paroxysmal nocturnal hemoglobinuria, and dysfibrinogenemia.

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