Ann Intern Med. 2015;163:701-711
Background:
The evaluation of pulmonary embolism is a nearly daily challenge in the emergency department. The d-dimer test is frustrating in its high sensitivity but poor specificity and our current CT pulmonary embolism scans expose the patient to a high dose of radiation. It is not the patients with abnormal vital signs, pleuritic chest pain and dyspnea who create a diagnostic dilemma but instead the patients with atypical symptoms such as the patient who endorses only mild dyspnea on exertion with no risk factors and normal vital signs.
This article focuses on streamlining the workup of pulmonary embolism. Medicine is an art and there will be occasional patients that you do further evaluation on despite being low risk however I think the best practice advice is helpful for decreasing exposure to radiation and resource utilization.
Type of study:
Clinical guideline (review of literature on pulmonary embolism)
Risk of CT scans: cancer, dye-induced anaphylaxis, acute kidney injury
Interesting point: although the incidence of PE has increased with the increased use CT studies, the overall rate of mortality has not changed.
Best Practice Advice 1: Clinicians should use validated clinical prediction rules to estimate pretest probability in patients in whom acute PE is being considered.
Calculate a Wells score. If 0, calculate a PERC score.
Wells Criteria:
PERC Guideline:
Best Practice Advice 2: Clinicians should not obtain d-dimer measurements or imaging studies in patients with a low pretest probability of PE and who meet all Pulmonary Embolism Rule-Out Criteria.
If both Wells and PERC scores are 0, you are done. Risk of PE outweighs risk of radiation.
Best Practice Advice 3: Clinicians should obtain a high-sensitivity d-dimer measurement as the initial diagnostic test in patients who have an intermediate pretest probability of PE or in patients with low pretest probability of PE who do not meet all Pulmonary Embolism Rule-Out Criteria. Clinicians should not use imaging studies as the initial test in patients who have a low or intermediate pretest probability of PE.
Before highly sensitive d-dimers, imaging was recommended for intermediate risk patients. With highly sensitive d-dimer, if d-dimer is negative in intermediate risk patient, you are done.
Proposed guideline:
Best Practice Advice 4: Clinicians should use age-adjusted d-dimer thresholds (age × 10 ng/mL rather than a generic 500 ng/mL) in patients older than 50 years to determine whether imaging is warranted.
The threshold for a positive d-dimer in Epic is now age-adjusted.
Best Practice Advice 5: Clinicians should not obtain any imaging studies in patients with a d-dimer level below the age-adjusted cutoff.
Best Practice Advice 6: Clinicians should obtain imaging with CTPA in patients with high pretest probability of PE. Clinicians should reserve V/Q scans for patients who have a contraindication to CTPA or if CTPA is not available. Clinicians should not obtain a d-dimer measurement in patients with high pretest probability of PE.
If your patient has breast cancer, recently had a total hip arthroplasty, has previous history of PE, has hemoptysis and has a heart rate of 120, do not get a d-dimer. Proceed to CT. This is obvious.
As a bonus, pulmonary embolism in pregnancy!
Background:
Evaluation of pulmonary embolism in pregnancy is even more challenging. Many symptoms that occur due to physiologic changes in pregnancy (dyspnea, increased heart rate, lower extremity swelling) are also symptoms of pulmonary embolism. Physicians are hesitant to expose a pregnant woman to radiation.
The American College of Obstetricians and Gynecologists’ clinical guideline on evaluation of pulmonary embolism in pregnancy draws from the recommendations from the American Thoracic and American Thoracic Radiology Societies.
An Official American Thoracic Society/Society of Thoracic Radiology Clinical Practice Guideline: Evaluation of Suspected Pulmonary Embolism In Pregnancy
Am J Respir Crit Care Med Vol 184. pp 1200–1208, 2011
Their recommendations are summarized below:
This guideline does not include use of a d-dimer. One study showed that in pregnancy, the sensitivity of a d-dimer is low (around 70%) whereas the specificity is very low (around 15%). The normal d-dimer rises throughout pregnancy.
ACOG has recommended starting with lower extremity ultrasounds in patients with leg symptoms. If positive, treat for DVT and suspected PE.
If no leg symptoms, they recommend a chest xray followed by either CT PE study or VQ scan. This guideline is 5 years old and I think the recommendation for VQ scan is outdated. Most radiologists and OB/GYNs I have spoken to recently recommend CT PE study which contradicts the ACOG guideline.
Randomized controlled studies looking at risk of CT on fetus obviously cannot be done however the amount of radiation from CT theoretically should not result in congenital abnormalities. The risk of PE to mom and baby outweighs the risk of radiation.
The author of the PERC rule, Dr. Jeff Kline, has noted that 60% of healthy patients in normal pregnancy will have a raised D-dimer. He proposes using the PERC rule, adapted for normal physiological change in heat rate during pregnancy, in combination with an altered D-dimer threshold to risk stratify pregnant patients.
First trimester: Modified PERC, heart rate >105 and D-dimer threshold 50% higher than normal cut-off.
Second trimester: Modified PERC, heart rate >105 and D-dimer threshold 100% higher than normal cut-off.
Third trimester: Modified PERC, heart rate >105 and D-dimer threshold 125% higher than normal cut-off.
Not certain that this is ready for prime time yet but interesting.
ACOG guidelines:
1. In pregnant women with suspected PE, D-dimer should not be used to exclude PE.
2. In pregnant women with suspected PE and signs and symptoms of deep venous thrombosis (DVT), perform bilateral venous compression ultrasound (CUS) of lower extremities, followed by anticoagulation treatment if positive and by further testing if negative.
3. In pregnant women with suspected PE and no signs and symptoms of DVT, perform studies of the pulmonary vasculature rather than CUS of the lower extremities.
4. In pregnant women with suspected PE, order CXR as the first radiation-associated procedure in the imaging work-up.
5. In pregnant women with suspected PE and a normal CXR, order a lung scintigraphy (V/Q scan) as the next imaging test rather than computed tomographic pulmonary angiography (CTPA).
6. In pregnant women with suspected PE and a nondiagnostic V/Q scan, obtain further diagnostic testing rather than clinical management alone. In patients with a nondiagnostic V/Q scan in whom a decision is made to further investigate, order CTPA rather than digital subtraction angiography (DSA).
7. In pregnant women with suspected PE and an abnormal CXR, order CTPA as the next imaging test rather than lung scintigraphy.
Questions:
1. If the patient is low risk by Wells criteria and PERC negative, risk of pulmonary embolism is lower than risk of radiation and no further evaluation with imaging should be performed.
a. True
b. False
2. How do you calculate an age-adjusted d-dimer?
a. age x 10
b. age x 20
c. age x 30
d. age x 40
3. What is the initial test of choice in a pregnant patient in whom you are concerned about pulmonary embolism who presents with leg symptoms?
a. Lower extremity ultrasounds then anticoagulation for DVT and presumed PE if positive
b. Chest xray
c. CT PE Study
d. D-dimer
4. ACOG recommends: In pregnant women with suspected PE, D-dimer should not be used to exclude PE.
a. True
b. False
5. ACOG recommends: In pregnant women with suspected PE and a normal CXR, order a lung scintigraphy (V/Q scan) as the next imaging test rather than computed tomographic pulmonary angiography (CTPA).
a. True
b. False
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