Venous Thromboembolism: Low Dose Heparin for DVT/PE Prophylaxis

Authors

Rogers, Frederick B. MD; Cipolle, Mark D. MD, PhD; Velmahos, George MD, PhD; Rozycki, Grace MD; Luchette, Fred A. MD

Author Information

From the University of Vermont, Department of Surgery, Fletcher Allen Health Care (F.B.R.), Burlington, Vermont, Department of Surgery, Lehigh Valley Hospital (M.D.C.), Allentown, Pennsylvania, Department of Surgery, Division of Trauma and Critical Care, University of Southern California (G.V.), Los Angeles, California, Department of Surgery, Emory University School of Medicine, Atlanta, Georgia, and Department of Surgery, Division of Trauma, Critical Care, and Burns, Loyola University Medical Center (F.A.L.), Maywood, Illinois.

Submitted for publication September 1, 2001.

Accepted for publication March 15, 2002.

Any reference in this guideline to a specific commercial product, process, or service by trade name, trademark, or manufacturer does not constitute or imply an endorsement, recommendation, or any favoritism by the authors or EAST. The views and opinions of the authors do not necessarily state or reflect those of EAST and shall not be used for advertising or product endorsement purposes.

Address for reprints: Frederick B. Rogers, MD, University of Vermont Department of Surgery, Fletcher Allen Health Care, 111 Colchester Avenue, Burlington, VT 05401; email: frederick.rogers@vtmednet.org.

Statement of the Problem

The fact that DVT and pulmonary embolism (PE) occur after trauma is incontrovertible. The optimal mode of prophylaxis has yet to be determined. Low-dose heparin (LDH), given in doses of 5,000 units subcutaneously two or three times daily, represents one pharmacologic treatment modality for prophylaxis against DVT/PE.

In contrast, LDH has not been shown to be particularly effective in preventing VTE in trauma patients. Three recent prospective trials demonstrated that LDH was no better in preventing DVT than no prophylaxis at all in patients with an ISS > 9. Sample sizes in these studies were small, and hence a type II statistical error cannot be excluded. The results of LDH use in trauma, with regard to PE, are even more vague.

Process

A MEDLINE review from 1966 to the present revealed several hundred articles related to the use of LDH in medical and general surgical patients. Only the nine articles related to the use of LDH in trauma patients were used for the following recommendations (Table 2).

Recommendations

A. Level I: A Level I recommendation on this topic cannot be supported because of insufficient data.

B. Level II: Little evidence exist to support the benefit of LDH as a sole agent for prophylaxis in the trauma patient at high-risk for VTE.^{[3][7][10][14][20-22]}

C. Level III: For patients in whom bleeding could exacerbate injuries (such as those with intracranial hemorrhage, incomplete spinal cord injuries, intraocular injuries, severe pelvic or lower extremity injuries with traumatic hemorrhage, and intra-abdominal solid organ injuries being managed nonoperatively), the safety of LDH has not been established, and an individual decision should be made when considering anticoagulant prophylaxis.

Scientific Foundation

Heparin is a naturally occurring polysaccharide varying in molecular weight from 2,000 to 40,000. LDH augments the activity of antithrombin III, a potent, naturally occurring inhibitor of activated factor X (Xa) and thrombin, which produces interruption of both the intrinsic and extrinsic pathways. Low-dose heparin causes only minimal or no change in conventional clotting tests, such as the partial thromboplastin time.

Studies on the use of LDH in trauma patients are inconclusive. In addition, many of these studies are single-institution studies with small sample sizes and lack randomization. These studies are summarized in Table 2.^[7][20][21] Studies with larger sample sizes and randomization will be discussed herein.^{[3][5][10][14][17][22]}

Knudson et al.^[3] reported on 251 patients in a cohort study who received LDH, a pneumatic compression device (PCD), or no prophylaxis. These authors failed to show any effectiveness with prophylaxis in most trauma patients, except in the subgroup of patients with neurotrauma in which PCD was more effective in preventing DVT than control. Upchurch et al.^[14] compared 66 intensive care unit (ICU)-dependent trauma patients who received either LDH or no VTE prophylaxis. No significance difference was seen in VTE rates between the two groups. In this same study, the authors performed a meta-analysis of the current literature concerning the use of LDH in 1,102 trauma patients. This meta-analysis demonstrated no benefit of LDH as prophylaxis compared with no prophylaxis (10% vs. 7%;p = 0.771). Geerts et al.^[17] randomized 344 trauma patients to receive low-molecular-weight heparin (LMWH) or LDH and found significantly fewer DVTs with LMWH than with LDH (31% vs. 44%, p = 0.014 for all DVT; and 15% vs. 6%, p = 0.012 for proximal DVT). This study had no control group. However, when compared with the predicted DVT rate if the study patients had not received prophylaxis, the risk reduction for LDH was only 19% for DVT and only 12% for proximal DVT, whereas the comparative risk reductions for LMWH were 43% and 65%, respectively. Napolitano et al.^[10] used a serial ultrasound screening protocol for DVT in 437 patients who were given four types of prophylaxis (LDH, PCD, LDH and PCD, and no prophylaxis) according to their attending surgeon's preference. No significant difference was seen in DVT rates between groups (8.6%, 11.6%, 8.0%, and 11.9%, respectively).

Velmahos et al.^[5] looked at the use of LDH and PCD or PCD alone in 200 critically injured patients who were then followed with biweekly Doppler examinations to detect proximal lower extremity DVT. The incidence of DVT was 13% overall, and no difference was seen between the two groups. The majority (58%) of DVT developed in the first 2 weeks. In a meta-analysis conducted under the auspices of the Agency for Healthcare Research and Quality, Velmahos and colleagues^[22] looked at all randomized controlled and nonrandomized studies on the use of LDH in trauma patients. The four randomized controlled studies on the use of LDH in trauma patients showed no difference in the incidence of DVT between those receiving LDH versus no prophylaxis (OR, 0.965; 95% CI, 0.360-2.965; vs. OR, 1.33; 95% CI, 0.360-2.965).

Summary

In summary, to date, LDH has very little proven efficacy in the prevention of VTE after trauma. Most studies on the use of LDH in trauma patients suffer from severe methodologic errors, poor study design, and small sample size, suggesting the possibility of a type II statistical error.

Future Investigation

Enough accumulated data do not exist to support the use of LDH in a trial in high-risk trauma patients. Future studies should focus on the potential benefit of more efficacious agents such as low-molecular-weight heparin.

Acknowledgment

We thank Jody Ciano for her help in the preparation of this article.

References

1. Pasquale M, Fabian TC, and the EAST Ad Hoc Committee on Guidelines Development. Practice management guidelines for trauma from the Eastern Association for the Surgery of Trauma. J Trauma. 1998; 44: 941-957.
2. Interim Manual for Clinical Practice Guideline Development. Rockville, MD: Agency for Health Care Policy and Research; May 1991.
3. Knudson MM, Lewis FR, Clinton A, et al. Prevention of venous thromboembolism in trauma patients. J Trauma. 1994; 37: 480-487.
4. Kudsk KA, Fabian T, Baum S, et al. Silent deep venous thrombosis in immobilized multiple trauma patients. Am J Surg. 1989; 158: 515-519.
5. Velmahos GC, Nigro J, Tatevossian R, et al. Inability of an aggressive policy of thromboprophylaxis to prevent deep venous thrombosis (DVT) in critically injured patients: are current methods of DVT prophylaxis insufficient? J Am Coll Surg. 1998; 187: 529-533.
6. Spain DA, Richardson JD, Polk JR, et al. Venous thromboembolism in the high-risk trauma patient: do risks justify aggressive screening and prophylaxis? J Trauma. 1997; 42: 463-469.
7. Dennis JW, Menawat S, Von Thron J, et al. Efficacy of deep venous thrombosis prophylaxis in trauma patients and identification of high-risk groups. J Trauma. 1993; 35: 132-139.
8. Meyer CS, Blebea J, Davis K Jr, Fowl R, Kempsczinski RF. Surveillance venous scans for deep venous thrombosis in multiple trauma patients. Ann Vasc Surg. 1995; 9: 109-114.
9. Piotrowski JJ, Alexander JJ, Brandt CP, et al. Is deep vein thrombosis surveillance warranted in high-risk patients? Am J Surg. 1996; 172: 210-213.
10. Napolitano LM, Garlapati VS, Heard SO, et al. Asymptomatic deep venous thrombosis in the trauma patient: is an aggressive screening protocol justified? J Trauma. 1995; 39: 651-659.
11. Geerts WH, Code KJ, Jay RM, et al. A prospective study of venous thromboembolism after major trauma. N Engl J Med. 1994; 331: 1601-1606.
12. Knudson MM, Morabito D, Paiement GD, et al. Use of low molecular weight heparin in preventing thromboembolism in trauma patients. J Trauma. 1996; 41: 446-459.
13. Abelseth G, Buckley RE, Pineo GE, et al. Incidence of deep vein thrombosis in patients with fractures of the lower extremity distal to the hip. J Orthop Trauma. 1996; 10: 230-235.
14. Upchurch GR Jr, Demling RH, Davies J, et al. Efficacy of subcutaneous heparin in prevention of venous thromboembolic events in trauma patients. Am Surg. 1995; 61: 749-755.
15. Knudson MM, Collins JA, Goodman SB, et al. Thromboembolism following multiple trauma. J Trauma. 1992; 32: 2-11.
16. Hill SL, Berry RE, Ruiz AJ. Deep venous thrombosis in the trauma patient. Am Surg. 1994; 60: 405-408.
17. Geerts WH, Jay RM, Code KI, et al. A comparison of low-dose heparin with low-molecular weight heparin as prophylaxis against venous thromboembolism after major trauma. N Engl J Med. 1996; 335: 701-707.
18. Waring WP, Karunas RS. Acute spinal cord injury and the incidence of clinically occurring thromboembolic disease. Paraplegia. 1991; 29: 8-16.
19. Spannagel U, Kujath P. Low molecular weight heparin for the prevention of thromboembolism in outpatients immobilized by plaster cast. Semin Thromb Hemost. 1993; 19 (suppl 1): 131-141.
20. Shackford SR, Davis JW, Hollingsworth-Fridlund P, et al. Venous thromboembolism in patients with major trauma. Am J Surg. 1990; 159: 365-369.
21. Ruiz AJ, Hill SL, Berry RE. Heparin, deep venous thrombosis, and trauma patients. Am J Surg. 1991; 162: 159-162.
22. Velmahos GC, Kern J, Chan L, et al. Prevention of venous thromboembolism after injury: an evidence-based report-part I: analysis of risk factors and evaluation of the role of vena cava filters. J Trauma. 2000; 49: 132-139.
23. Gardner AMN, Fox RH. The venous pump of the human foot: preliminary report. Bristol Med Chir J. 1983; 98: 109-112.
24. Laverick MD, McGivern RC, Crone MD, Mollan RAB. A comparison of the effects of electrical calf muscle stimulation and the venous foot pump on venous blood flow in the lower leg. Phlebology. 1990; 5: 285-290.
25. Spain DA, Bergamini, Hoffman JF, et al. Comparison of sequential compression devices and foot pumps for prophylaxis of deep venous thrombosis in high-risk trauma patients.Am Surg. 1998;64:522-526.
26. Anglen JO, Bagby C, George R. A randomized comparison of sequential-gradient calf compression with intermittent plantar compression for prevention of venous thrombosis in orthopedic trauma patients: preliminary results. Am J Orthop. 1998; 33: 53-57.
27. Gardner AM, Fox RH, Lawrence C, et al. Reduction of post-traumatic swelling and compartment pressure by impulse compression of the foot. J Bone Joint Surg Br. 1990; 72: 810-815.
28. Morgan RH, Carolan G, Psaila JV, et al. Arterial flow enhancement by impulse compression. Vasc Surg. 1991; 25: 8-15.
29. Abu-Own A, Cheatle T, Scurr JH, et al. Effects of intermittent pneumatic compression of the foot on microcirculatory function in arterial disease. Eur J Vasc Surg. 1993; 7: 488-492.
30. Anglen JO, Goss K, Edwards J, Heickfeldt RE. Foot pump prophylaxis for deep venous thrombosis: the rate of effective usage in trauma patients. Am J Orthop. 1998; 27: 580-582.
31. Comerota AJ, Katz ML, White JV. Why does prophylaxis with external pneumatic compression for deep vein thrombosis fail? Am J Surg. 1992; 164: 265-268.
32. Caprini JA, Arcelus JI, Hoffman K, et al. Prevention of venous thromboembolism in North America: results of a survey among general surgeons. J Vasc Surg. 1994; 20: 751-758.
33. Pidala MJ, Donovan DL, Kepley RF. A prospective study on intermittent pneumatic compression in the prevention of deep vein thrombosis in patients undergoing total hip or total knee replacement. Surg Gynecol Obstet. 1992; 175: 47-51.
34. Woolson ST, Watt JM. Intermittent pneumatic compression to prevent proximal deep venous thrombosis during and after total hip replacement: a prospective, randomized study of compression alone, compression and aspirin, and compression and low-dose warfarin. J Bone Joint Surg Am. 1991; 73: 507-512.
35. Gersin K, Grindlinger GA, Lee V, et al. The efficacy of sequential compression devices in multiple trauma patients with severe head injury. J Trauma. 1994; 37: 205-208.
36. Fisher CG, Blachut PA, Salvian AJ, et al. Effectiveness of pneumatic leg compression devices for the prevention of thromboembolic disease in orthopaedic trauma patients: a prospective, randomized study of compression alone versus no prophylaxis. J Orthop Trauma. 1995; 9: 1-7.
37. Keith SL, McLaughlin DJ, Anderson FA Jr, et al. Do graduated compression stockings and pneumatic boots have an additive effect on the peak velocity of venous blood flow? Arch Surg. 1992; 127: 727-730.
38. Inada K, Koike S, Shirai N, et al. Effects of intermittent pneumatic leg compression for prevention of postoperative deep venous thrombosis with special reference to fibrinolytic activity. Am J Surg. 1988; 155: 602-605.
39. Jacobs DG, Piotrowski JJ, Hoppensteadt DA, et al. Hemodynamic and fibrinolytic consequences of intermittent pneumatic compression: preliminary results. J Trauma. 1996; 40: 710-717.
40. Bradley JG, Krugener GH, Jager HJ. The effectiveness of intermittent plantar venous compression in prevention of deep venous thrombosis after total hip arthroplasty. J Arthroplasty. 1993; 8: 57-61.
41. Davidson JE, Willms DC, Hoffman MS. Effect of intermittent pneumatic leg compression on intracranial pressure in brain-injured patients. Crit Care Med. 1993; 21: 224-227.
42. Parra RO, Farber R, Feigl A. Pressure necrosis from intermittent-pneumatic-compression stockings [letter]. N Engl J Med. 1989; 321: 1615.
43. Lachmann EA, Rook JL, Tunkel R, et al. Complications associated with intermittent pneumatic compression. Arch Phys Med Rehabil. 1992; 73: 482-485.
44. Greenfield LJ, Proctor MC, Rodriguez JL, et al. Posttrauma thromboembolism prophylaxis. J Trauma. 1997; 42: 100-103.
45. Monreal M, Lafoz E, Navarro A, et al. A prospective double-blind trial of a low molecular weight heparin once daily compared with conventional low-dose heparin three times daily to prevent pulmonary embolism and venous thrombosis in patients with hip fracture. J Trauma. 1989; 29: 873-875.
46. Green D, Lee MY, Lim AC, et al. Prevention of thromboembolism after spinal cord injury using low-molecular-weight heparin. Ann Intern Med. 1990; 113: 571-574.
47. Litz RJ, Hubler M, Koch T, Albrecht DM. Spinal-epidural hematoma following epidural anesthesia in the presence of antiplatelet and heparin therapy. Anesthesiology. 2000; 95: 1031-1033.
48. Hirsh J, Warkentin TE, Shaughnessy SG, et al. Heparin and low molecular weight heparin: mechanism of action, pharmacokinetics, dosing, monitoring, safety. Chest. 2001; 119: 64S-94S.
49. Osler TM, Rogers FB. Prophylaxis against venous thromboembolism after major trauma. N Engl J Med. 1997; 336: 586.
50. Turpie AGG, Gallus AS, Hoek JA. A synthetic pentasaccharide for the prevention of deep-vein thrombosis after total hip replacement. N Engl J Med. 2001; 344: 619-625.
51. Bauer KA, Eriksson BI, Lassen MR, et al. Fondaparinux compared with enoxaparin for the prevention of venous thromboembolism after elective major knee surgery. N Engl J Med. 2001; 345: 1305-1310.
52. Webb LX, Rush PT, Fuller SB, et al. Greenfield filter prophylaxis of pulmonary embolism in patients undergoing surgery for acetabular fracture. J Orthop Trauma. 1992; 6: 139-145.
53. Jarrell BE, Posuniak E, Roberts J, et al. A new method of management using the Kim-Ray Greenfield filter for deep venous thrombosis and pulmonary embolism in spinal cord injury. Surg Gynecol Obstet. 1983; 157: 316-320.
54. Cipolle M, Marcinczyk M, Pasquale M, et al. Prophylactic vena caval filters reduce pulmonary embolism in trauma patients [abstract]. Crit Care Med. 1995; 23: A93.
55. Rodriguez JL, Lopez JM, Proctor MC, et al. Early placement of prophylactic vena caval filters in injured patients at high-risk for pulmonary embolism. J Trauma. 1996; 40: 797-804.
56. Rogers FB, Shackford SR, Ricci MA, et al. Routine prophylactic vena cava filter insertion in severely injured trauma patients decreases the incidence of pulmonary embolism. J Am Coll Surg. 1995; 180: 641-647.
57. Rosenthal D, McKinsey JF, Levy AM, et al. Use of the Greenfield filter in patients with major trauma. Cardiovasc Surg. 1994; 2: 52-55.
58. Wilson JT, Rogers FB, Wald SL, et al. Prophylactic vena cava filter insertion in patients with traumatic spinal cord injury: preliminary results. Neurosurgery. 1994; 35: 234-239.
59. Winchell RJ, Hoyt DB, Walsh JC, et al. Risk factors associated with pulmonary embolism despite routine prophylaxis: implications for improved protection. J Trauma. 1994; 37: 600-606.
60. Zolfaghari D, Johnson B, Weireter LJ, et al. Expanded use of inferior vena cava filters in the trauma population. Surg Annu. 1995; 27: 99-105.
61. Rogers FB, Shackford SR, Wilson J, et al. Prophylactic vena cava filter insertion in severely injured trauma patients: indications and preliminary results. J Trauma. 1993; 35: 637-642.
62. Patton JH Jr, Fabian TC, Croce MA, et al. Prophylactic Greenfield filter: acute complications and long-term follow up. J Trauma. 1996; 41: 231-237.
63. Leach TA, Pastena JA, Swan KG. Surgical prophylaxis for pulmonary embolism. Am Surg. 1994; 60: 292-295.
64. Khansarinia S, Dennis JW, Veldenz HC, Butcher JL, Hartland L. Prophylactic Greenfield filter placement in selected high-risk trauma patients. J Vasc Surg. 1995; 22: 235-236.
65. Gosin JS, Graham AM, Ciocca RG, Hammond JS. Efficacy of prophylactic vena cava filters in high-risk trauma patients. Ann Vasc Surg. 1997; 11: 100-105.
66. Sekharan J, Dennis JW, Miranda FE, et al. Long-term follow-up of prophylactic Greenfield filters in multisystem trauma patients. J Trauma. 2001; 51: 1087-1091.
67. Greenfield LJ, Proctor MC, Michaels AJ, Taheri PA. Prophylactic vena cava filters in trauma: the rest of the story. J Vasc Surg. 2000; 32: 490-495.
68. Van Natta TL, Morris JA Jr, Eddy VA, et al. Elective bedside surgery in critically injured patients is safe and cost effective. Ann Surg. 1998; 227: 618-624.
69. Langan EM III, Miller RS, Casey WJ, et al. Prophylactic inferior vena cava filters in trauma patients at high-risk: follow-up examination and risk/benefit assessment. J Vasc Surg. 1999; 30: 484-488.
70. Velmahos GC, Kern J, Chan L, et al. Prevention of venous thromboembolism after trauma: an evidence-based report-part II: analysis of risk factors and evaluation of the role of vena cava filters. J Trauma. 2000; 49: 140-144.
71. Greenfield LJ, Proctor MC. Recurrent thromboembolism in patients with vena cava filters. J Vasc Surg. 2001; 33: 510-514.
72. Golueke PJ, Garrett WV, Thompson JE, et al. Interruption of the vena cava by means of the Greenfield filter: expanding the indications. Surgery. 1988; 103: 111-117.
73. Rohrer MJ, Scheidler MG, Wheeler HB, et al. Extended indications for placement of inferior vena cava filter. J Vasc Surg. 1989; 10: 44-50.
74. Ferris EJ, McCowan TC, Carver DK, et al. Percutaneous inferior vena cava filters: follow-up of seven designs in 320 patients. Radiology. 1993; 188: 851-856.
75. Nunn CR, Neuzil D, Naslund T, et al. Cost-effective method for bedside insertion of vena cava filters in trauma patients. J Trauma. 1997; 45: 752-758.
76. Headrick JR, Barker DE, Pate LM, Horne K, Russell WL, Burns RP. The role of ultrasonography and inferior vena cava filter placement in high-risk trauma patients. Am Surg. 1997; 63: 1-8.
77. McMurtry AL, Owings JT, Anderson JT, Battistella FD, Gosselin R. Increase use of prophylactic vena cava filters in trauma patients failed to decrease overall incidence of pulmonary embolism. J Am Coll Surg. 1999; 189: 314-320.
78. Ashley DW, Gamblin TC, Burch ST, Solis MM. Accurate deployment of vena cava filters: comparison of intravascular ultrasound and contrast venography. J Trauma. 2001; 50: 975-981.
79. Greenfield LJ. Post trauma thromboembolism prophylaxis. Paper presented at: Eighth Annual Meeting of the American Venous Forum, February 1996; San Diego, CA.
80. Tola JC, Hotzman R, Lottenberg L. Bedside placement of inferior vena cava filters in the intensive care unit. Am Surg. 1999; 65: 833-837.
81. Lorch H, Welger D, Wagner V, et al. Current practice of temporary vena cava filter insertion: a multicenter registry. J Vasc Intervent Radiol. 2000; 11: 83-88.
82. Neuerburg JM, Gunther RW, Vorwerk D, et al. Results of a multicenter study of the retrievable tulip vena cava filter: early clinical experience. Cardiovasc Intervent Radiol. 1997; 20: 10-16.
83. Wheeler HB, Anderson FA Jr. Diagnostic methods for deep vein thrombosis. Haemostasis. 1995; 25: 6-26.
84. Wheeler HB, Anderson FA Jr. Use of noninvasive tests as the basis for treatment of deep vein thrombosis. In: Bernstein EF, ed. Vascular Diagnosis. 4th ed. St. Louis: Mosby; 1993: 1894-1912.
85. Burns GA, Cohn SM, Frumento RJ, et al. Prospective ultrasound evaluation of venous thrombosis in high-risk trauma patients. J Trauma. 1993; 35: 405-408.
86. Napolitano LM, Garlapati VS, Heard SO, et al. Asymptomatic deep venous thrombosis in the trauma patient: is an aggressive screening protocol justified? J Trauma. 1995; 39: 651-659.
87. Meythaler JM, DeVivo MJ, Hayne JB. Cost-effectiveness of routine screening for proximal deep venous thrombosis in acquired brain injury patients admitted to rehabilitation. Arch Phys Med Rehabil. 1996; 77: 1-5.
88. White RH, Goulet JA, Bray TJ, et al. Deep-vein thrombosis after fracture of the pelvis: assessment with serial duplex-ultrasound screening. J Bone Joint Surg Am. 1990; 72: 495-500.
89. Meredith JW, Young JS, O'Neil EA, et al. Femoral catheters and deep venous thrombosis: a prospective evaluation of venous duplex sonography. J Trauma. 1993; 35: 187-191.
90. Brasel KJ, Borgstrom DC, Weigelt JA. Cost effective prevention of pulmonary embolus in high-risk trauma patients. J Trauma. 1997; 42: 456-463.
91. Agnelli G, Radicchia S, Nenci GG. Diagnosis of deep vein thrombosis in asymptomatic high-risk patients. Haemostasis. 1995; 25: 40-48.
92. Wells PS, Lensing AW, Davidson BL, et al. Accuracy of ultrasound for the diagnosis of deep venous thrombosis in asymptomatic patients after orthopedic surgery: a meta-analysis. Ann Intern Med. 1995; 122: 47-54.
93. Prandoni P, Bernardi E. Upper extremity deep vein thrombosis. Curr Opin Pulm Med. 1999; 5: 222-226.
94. Chu DA, Ahn JH, Ragnarson KT, et al. Deep venous thrombosis: diagnosis in spinal cord injured patients. Arch Phys Med Rehabil. 1985; 66: L365-L368.
95. Myllynen P, Kammonen M, Rokkanen P, et al. Deep venous thrombosis and pulmonary embolism in patients with acute spinal cord injury: a comparison with nonparalyzed patients immobilized due to spinal fractures. J Trauma. 1985; 25: 541-543.
96. Brach BB, Moser KM, Cedar L, et al. Venous thrombosis in acute spinal cord paralysis. J Trauma. 1977; 17: 289-292.
97. Satiani B, Falcone R, Shook L, Price J. Screening for major deep venous thrombosis in seriously injured patients: a prospective study. Ann Vasc Surg. 1997; 11: 626-629.
98. Sandler DA, Martin JF, Duncan JS, et al. Diagnosis of deep-vein thrombosis: comparison of clinical evaluation, ultrasound, plethysmography and venoscan with x-ray venogram. Lancet. 1984; 2: 716-719.
99. Burke B, Sostman HD, Carroll BA, Witty LA. The diagnostic approach to deep venous thrombosis. Clin Chest Med. 1995; 16: 253-268.
100. Freeark RJ, Boswick J, Fardin R. Posttraumatic venous thrombosis. Arch Surg. 1967; 95: 567-575.
101. Montgomery KD, Potter HG, Helfet DL. Magnetic resonance venography to evaluate the deep venous system of the pelvis in patients who have an acetabular fracture. J Bone Joint Surg Am. 1995; 77: 1639-1649.
102. Rabinov K, Paulin S. Roentgen diagnosis of venous thrombosis in the leg. Arch Surg. 1972; 104: 134-144.
103. Bettmann MA, Robbins A, Braun SD, et al. Contrast venography of the leg: diagnostic efficacy, tolerance, and complication rates with ionic and nonionic contrast media. Radiology. 1987; 165: 113-116.
104. Kakkar VV, Howe CT, Nicolaides AN, et al. Deep vein thrombosis of the leg: is there a high-risk group? Am J Surg. 1970; 120: 527-530.
105. Brathwaite CE, Mure AJ, O'Malley K, et al. Complications of anticoagulation for pulmonary embolism in low risk trauma patients. Chest. 1993; 104: 718-720.

Table

Lose-Dose Heparin