Pulmonary embolism is a serious condition that is important to diagnose and treat effectively. The mortality of pulmonary embolism left untreated is approximately 33%.
Diagnosis of Pulmonary Embolism
In the past two-three years there have been two large studies on the diagnosis of PE that have been published. The Christopher study and PIOPED II (with associated editorial).
The first step in diagnosis is to establish what you believe the clinical probability of PE is. For this, I use the Wells Criteria for PE:
- PE is the most likely diagnosis (Score 3 Points)
- Clinical DVT on history and exam (Score 3 Points)
- Heart rate >100 (Score 1.5 Points)
- Immobility >3 days or surgery in last 4 weeks (Score 1.5 Points)
- PMH of PE or DVT (Score 1.5 Points)
- Haemoptysis (Score 1 Point)
- Malignancy within 6 months or palliative (Score 1 Point)
less than 2 = "Low" (1.3% of PE in original study)
2-6 =" Medium" (~17% chance of PE in original study)
>6 = High risk (37.5% Chance of PE in original study)
If the patient is low risk, I will perform a D-dimer assay and if negative I feel it is safe to say, based on the Christoper and other studies, that PE is excluded.
If the patient is medium or high risk, the D-dimer will not help you. They need some other form of investigation. I then think about which investigations are available, how well they perform, how long until I can get them and what contraindications the patient has.
V/Q Scan:
- Requires: Relatively normal chest x-ray and no significant COPD
- Difficult to get after hours (or even during normal hours)
- If positive PE is confirmed
- If negative PE is excluded
- Problem: "Low probability V/Q" is not normal, and not low enough to exclude PE and you will need a follow up test
- No radiation, no contrast, relatively easy to get (except after hours at some hospitals)
- Good at detecting symptomatic DVT, but relatively insensitive for asymptomatic DVT or pelvic DVT
- Will miss upper extremity sources
- I use this in a patient where V/Q isn't an option and I don't want to subject the patient to a CT angiogram if at all possible (i.e. contrast allergy).
- I also use doppler in patients for whom the V/Q is intermediate, or in whom the CT scan is negative/equivocal in whom there is still a significant post-test probability of PE (see CT scan, below)
- Rapidly becoming the most common test that we use and is readily available
- Contrast is used, so contrast allergy, contrast induced nephropathy are a concern
- Radiation exposure
- From PIOPED II (figure above) you can see that the performance characteristics of CT angiography are very dependent on the clinical probability and you should interpret them as such before making serious clinical decisions.
- High clinical probability -- Positive test rules in PE, negative test does not exclude (sensitivity 60%)
NB in the Christopher study <1.5> - Medium clinical probability -- Positive test essential rules in PE (PPV 92%), negative test performs well but could miss up to 10% (NPV 90%).
- Low clinical probability -- Negative study rules out PE, positive test positive predictive value only 60% so unless there is another compelling reason to anticoagulate perhaps other tests would be required.
- Supportive care
- Heparin -- either IV Heparin infusion, or low molecular weight heparin injection (I favor LMWH in most cases except for renal failure or high risk of bleeding)
- Long term anti-coagulation with coumadin or LMWH (duration depends on risk factors)
- Consider IVC filter -- UPDATE -- READ THIS and consider
- Can't anticoagulate (e.g. bleeding, other contraindication)
- Recurrent PE on appropriate therapy
- Unstable patient with large DVT
- Can't anticoagulate (e.g. bleeding, other contraindication)
"Massive PE" with hemodynamic instability -- there is little good evidence
Options include:
- Thrombolysis (either IV or IA) with TPA
- Clot fragmentation and aspiration (interventional radiology)
- Surgical thrombectomy
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