13: Pulmonary Embolism

INCIDENCE AND MORTALITY

Since the advent of CT pulmonary angiography, there has been a marked increase in the incidence of diagnosed pulmonary embolism (PE), from 62.1 to 112.3 cases per one hundred thousand, although it is still believed that more than half of all cases remain undetected. Concomitantly over the last 30 years, the incidence of pulmonary emboli in all hospitalized patients has tripled, from 0.5% to 1.5%.¹ Although the incidence of PE has increased markedly, the absolute mortality has not, suggesting a new over-diagnosis.^2,3

PATHOPHYSIOLOGY—RISK FACTORS

The pathogenesis of PE classically stems from Virchow's triad of endothelial injury, circulatory stasis and hypercoagulable state. Reversible risk factors include major factors such as surgery, hospitalization or plaster cast immobilization all within the prior month. Minor factors include estrogen therapy, pregnancy, prolonged travel >8 hours and or the major factors when they occurred 1 to 3 months before VTE diagnosis.⁴ Newer epidemiologic studies in the last several years have interestingly focused on physical inactivity, steroids and even blood type as potential risk factors.^5–7 In a study of 69,950 female nurses, PE risk was more than doubled in women who were sedentary compared with those who were more active.⁵ A population based case control study in Denmark recently showed that systemic steroids increased venous thromboembolism (VTE) risk two-fold.⁶ Finally, VTE patients were 2.21 times more likely to have non-O blood type than their control counterparts.⁷ Notwithstanding these interesting findings, the most common reversible risk factor for PE remains obesity, followed by cigarette smoking and hypertension⁸ (Table 13-1). In view of the multiplicity of risk factors, updated models—such as the IMPROVE risk assessment model—have been developed to guide appropriateness of VTE prophylaxis in hospitalized patients^9–11 (Table 13-2).

PATHOPHYSIOLOGY—THROMBOPHILIA ...