Pulmonary Thromboembolism

Trauma patients are at risk for the development of deep venous thrombosis (DVT) and consequent pulmonary thromboembolism (PTE) (444-446). The evolution of DVT involves interplay between blood stasis, endothelial injury and hypercoagulability. Risk

Fig. 46. Pulmonary fat embolism in a trauma case. Lung cut during autopsy. Numerous fat droplets on dissecting board (arrows). (Courtesy of Dr. C. Armstrong, London Health Sciences Centre, London, Ontario, Canada.)

Fig. 47. Pulmonary fat embolism, microscopic examination. (A) Intravascular vacuoles (formalin-fixed tissue H&E. Original magnification x200).(B) Multiple fat emboli (formalin-fixed tissue, postfixation with osmium tetroxide, original magnification x100). (C) Multiple fat emboli (fresh frozen tissue, oil-red-O stain; original magnification x100).

Fig. 47. Pulmonary fat embolism, microscopic examination. (A) Intravascular vacuoles (formalin-fixed tissue H&E. Original magnification x200).(B) Multiple fat emboli (formalin-fixed tissue, postfixation with osmium tetroxide, original magnification x100). (C) Multiple fat emboli (fresh frozen tissue, oil-red-O stain; original magnification x100).

Fig. 48. Bone marrow embolus (H&E, original magnification x100).

factors for DVT and PTE include the type of injury (fracture of a lower extremity or pelvis, head or spinal cord injury, vein trauma), age more than 40 yr, a thrombotic predisposition, prolonged time (>3 d) on a ventilator, coma, an indwelling central venous line, and performance of a major surgical procedure (444-451).

Most cases of DVT start in the calf veins and resolve spontaneously (452). DVT can develop in the extremity contralateral to the injury (448). The frequency of asymptomatic DVT in the lower extremities in trauma cases, as determined by venography, is high. A study of 716 patients admitted to a regional trauma unit showed DVT in about half of cases of injuries of the head, face, chest, or abdomen, in about two-thirds of pelvic and spinal trauma victims, and in more than three-fourths of individuals with femoral and tibial fractures (451). Extension into the proximal veins runs the risk of embolization (452). PTE is not necessarily preceded by clinical evidence of DVT (451 ). About half of patients with symptomatic proximal DVT, without PTE symptoms, have ventilationperfusion lung scan findings associated with a high probability of embolism (452). The clinical incidence of venous thromboembolic events (DVT, PTE) in admissions to US trauma centers was less than 1% in one study (447). Other studies have shown an incidence of PTE below 1% (445,451). The overall incidence of PTE in a series of pediatric trauma patients aged less than 19 yr, as documented in the US National Pediatric Trauma Registry, was 0.000069% (1.85% for spinal cord injury [449]).

Autopsy studies give a skewed perspective of the incidence of DVT and PTE (448). DVT has been found in 65% of fatal trauma cases, and PTE caused death in 20% (453,454). Young healthy individuals without cardiopulmonary disease can tolerate PTE (452). In about 10% of the PTE cases, there is sudden death (452). A large thrombo-embolus at the main pulmonary artery bifurcation (saddle embolus) or its main branches is usually rapidly fatal (Fig. 49; ref. 455). Smaller emboli filling more than half of secondary pulmonary artery branches can also be rapidly fatal (455).

Fig. 49. Bifurcation of main pulmonary artery opened to reveal "saddle" thromboembolus.

At autopsy, the pathologist must open and digitally examine the pulmonary artery bifurcation before the heart is removed from the body. If PTE is suspected by palpation, then the pulmonary artery can be clamped to prevent dislodging the embolus. The heart and lungs are then removed together and the pulmonary artery branches are opened further. Microscopic sections are required for confirmation of thromboembolism. Thigh and calf circumferences are compared to assess whether edema secondary to DVT has occurred. If there is a difference, then the bilateral femoral and popliteal veins, i.e., proximal veins, are opened. This limited dissection may be unproductive because the thrombus may have completely dislodged, lysed, or been situated at another site.

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