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Medical Author:

Charles Patrick Davis, MD, PhD

Charles Patrick Davis, MD, PhD

Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

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Medical Editor:

George Schiffman, MD, FCCP

George Schiffman, MD, FCCP

Dr. Schiffman received his B.S. degree with High Honors in biology from Hobart College in 1976. He then moved to Chicago where he studied biochemistry at the University of Illinois, Chicago Circle. He attended Rush Medical College where he received his M.D. degree in 1982 and was elected to the Alpha Omega Alpha Medical Honor Society. He completed his Internal Medicine internship and residency at the University of California, Irvine.

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Several risk factors can make a person more likely to develop a blood clot that can eventually break loose and travel to the lung. Virchow's triad explains the reasons why clots form. This triad includes 1) immobilization (which reduces flow), 2) damaged vessel wall (which forms a location for clot to start, and 3) Hypercoagulable state (which makes it easier for blood to clot.

• Immobilization: A stroke, broken bone, or spinal cord injury can result in confinement to bed so that clot formation can occur in either the arms or legs.
• Travel: Prolonged travel, such as sitting in an airplane or a long car trip, allows the blood to sit in the legs and increases the risk of clot formation.
• Recent surgery (includes hypercoagulable state due to surgical damage and the body trying to repair itself. It is also often associated with immobility and sometimes vessel damage depending on the surgery)
• Trauma or injury (especially to the legs)
• Obesity
• Heart disease (such as an irregular heartbeat)
• Burns
• Previous history of blood clot in the legs (DVTs) or pulmonary embolism

Conditions that increase clotting of the blood

• Pregnancy
• Cancer
• Estrogen therapy and oral contraceptives
• Certain protein and enzyme deficiencies

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