Difficult diagnosis to make – PE is misdiagnosed 80% of the time; conversely, up to 80% of diagnoses are missed
Dangerous condition
– present in 500,000 autopsies/yr; major cause of death: 50,000/yr; adequate prophylaxis can cut risk (ß mortality by 30% in one study of medical students)
High risk conditions
– orthopedic surgery (hip fracture, total hip replacement, total knee replacement); patients in these groups require immediate prophylaxis treatment (Heparin, high pressure stockings on lower extremities)
Other conditions – urologic surgery, general and gynecologic surgery, neurologic surgery, medical patients
Traditional methods
– ABG’s, V/Q, leg studies, angiogram
(1) ABG’s
– most patients with PE have abnormal ABG’s but not always, thus cannot be used to confirm/exclude a diagnosis
(2) V/Q
– compare ventilation (radiolabeled xenon) and perfusion (radiolabeled albumin) scans Þ conclusions made are low, intermediate, or high probability; should be initial diagnostic test in almost all patients
find matched defects
Þ intermediate/indeterminate probability for PE
find unmatched defect
Þ normal ventilation scan but abnormal perfusion scan Þ classic for PE Þ high probability
both scans are negative
Þ essentially rules out PE
PE probability
Ý with – Large perfusion defects; mismatched defects; multiple perfusion defects; perfusion defects in area of clear chest X-ray
Need to correlate clinical probability (patient risk factors: sedentary lifestyle, heart failure, sudden trauma, taking birth control pills) with the PE probability derived from V/Q scan
Þ increases yield tremendously
high probability and 90% clinical probability
Þ 96% chance of having PE
high probability and 10% clinical probability
Þ 50% chance of having PE
intermediate probability and 90% clinical probability
Þ 50% chance of having PE
(3) Leg studies
– Deep Venous Thrombosis (DVT) Þ clots can arise in heart, arms, pelvis but most (95%) from legs.
Can diagnose leg clots non-invasively with ultrasound or impedance plethysmography. Very good yield (up to 95%) in symptomatic patients but worse yield (down to 25%) if no leg symptoms.
Contrast venography more invasive but more accurate
Failure to find a leg clot does not rule out concern that a PE has occurred
(4) Angiogram
– look for filling defects, vessel cut off
specificity/sensitivity of this test are very high; however, angiography may "miss" some PE
Special techniques (selective injection, magnification techniques, image enhancement)
Ý the yield
mortality of 0.05 – 0.5% associated with angiography
Test is either positive or negative
(5) Newer modalities for Diagnosis
– D-dimer (useful to rule out disease if ELISA test negative); echocardiography (can detect clots in transit; often see enlarged RV; useful to rule disease in); spiral cut CT (detects larger clots but misses smaller clots); MRI (also detects larger clots but misses smaller clots; requires patient to hold breath; may be used if dye allergy)
Therapy for Pulmonary Emboli
(1) Heparin
– reacts with anti-thrombin III and neutralizes thrombin; neutralizes activated factor X
Major complications:
bleeding
(need to monitor coagulation times), hypokalemia, osteoporosis, white clot syndrome, thrombocytopenia
risk of bleeding ß with continuous therapy
primarily used for short term therapy (i.e., 10 days)
(2) Coumadin
(Warfarin)– inhibits production of vitamin K dependent clotting factors and inhibits activated factor X
do not administer too early or too late (has initial clotting effects so always start after administration of Heparin)
low dose therapy for approximately 6 months
(3) Low MW Heparin
– less bleeding than regular heparin with the same benefits
clearly more effective in some situations than regular heparin
currently used primarily for prophylaxis
more expensive
(4) Thrombolytic therapy
(i.e., t-PA, Streptokinase, Urokinase) – much greater potency for lysing clots
carries much higher risk of bleeding
contraindicated in patients with recent stroke or trauma
(5) Filter placement
(filters blood for clots) indications Þ recurrent PE despite optimum anticoagulation, PE with contraindication to anticoagulation, possible use if massive PE present