Pulmonary Embolism
By the end of this post you will be able to:
- Apply the Wells score — for both pulmonary embolism and deep vein thrombosis — and combine it with a D-dimer to decide who needs imaging.
- Risk-stratify a confirmed pulmonary embolism into high, intermediate and low risk, and match the treatment and the care setting to that risk.
- Select an anticoagulant and set its duration, including cancer-associated disease, and manage it around surgery.
TL;DR
What you need to know before seeing your first patient on your IM rotation with this condition
Estimated read time: 4 minutes
- What it is: A thrombus, usually from a deep vein of the leg or pelvis, lodged in the pulmonary arterial tree. Deep vein thrombosis (DVT) and pulmonary embolism (PE) are one disease — venous thromboembolism (VTE) — seen at two points.
- How it presents: Classically pleuritic chest pain, dyspnea and hemoptysis; in practice often only unexplained breathlessness or tachycardia. Syncope, hypotension or a new oxygen requirement suggest a large clot. There is no examination finding sensitive enough to rule it out.
- Initial tests to order: Every patient — Wells score first, because it determines what the D-dimer means. Then D-dimer, ECG, chest radiograph, troponin, complete blood count, creatinine and an arterial or venous gas if hypoxemic. Imaging — CT pulmonary angiogram (CTPA); a ventilation-perfusion scan if contrast is contraindicated, and compression ultrasound of the legs if the question is DVT.
- If unstable: hypotension (systolic <90 mmHg for 15 minutes, or needing vasopressors) defines high-risk PE. Call critical care and consider thrombolysis before the patient arrests, not after.
- If stable — the sequence: score Wells → interpret the D-dimer against that score → image if not excluded → start anticoagulation as soon as PE is likely, unless bleeding risk forbids it — apixaban 10 mg PO BID for 7 days, then 5 mg BID, or rivaroxaban 15 mg PO BID with food for 21 days, then 20 mg daily → risk-stratify → decide ward, monitored bed or ICU.
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Read Around the Case
Based on the Thrombosis Canada clinical guides, with the ESC 2019 acute PE guideline for risk stratification
Estimated read time: 12 minutes
1. Diagnosis — Wells, D-dimer and Who Gets Scanned
The single most common error is ordering a D-dimer before deciding how likely PE actually is. The score comes first, because it changes what the result means.
- Score before you send the D-dimer. The score decides what the number means — see the Clinical Pearl.
- The D-dimer threshold moves with the score. In PEGeD (Kearon, NEJM 2019, Canadian) the cut-off was 1000 µg/L when clinical probability was low and 500 µg/L when moderate — which safely avoided imaging in far more patients than a single fixed number.
- D-dimer is a rule-out test only. It is raised by infection, malignancy, surgery, pregnancy and age; a positive result narrows nothing.
- CTPA is the default confirmatory test. Use a ventilation-perfusion scan when contrast is contraindicated — renal impairment, contrast allergy — or to limit breast radiation in a young woman.
- Do not wait for imaging to anticoagulate when PE is likely and bleeding risk permits; the scan can be hours away.
The diagnostic sequence
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2. Deep Vein Thrombosis — The Other Half
Same disease, different Wells score, different first test. Do not carry the PE score across.
- Compression ultrasound is the first test, not a D-dimer, once DVT is likely.
- Proximal (popliteal and above) DVT is treated exactly as PE is.
- Isolated distal (calf) DVT can often be watched with serial ultrasound over 2 weeks rather than anticoagulated, if the patient is not high risk and symptoms are mild — a genuine choice, not an oversight.
- An unremarkable leg does not exclude PE. Most patients with PE have no clinical DVT at all.
≤1 = DVT unlikely → D-dimer; if negative, DVT is excluded. ≥2 = DVT likely → compression ultrasound.
3. Treatment — Anticoagulation, Duration and Surgery
Three decisions follow every confirmed VTE: which drug, for how long, and what happens when the patient needs an operation.
- A DOAC is first-line for most patients, and no longer needs a heparin lead-in — unless you choose dabigatran or edoxaban, which do.
- Cancer-associated VTE: CARAVAGGIO (NEJM 2020) showed apixaban non-inferior to dalteparin without excess major bleeding, so an oral agent is reasonable — with care in gastrointestinal and genitourinary tumors.
- Apixaban has the best bleeding profile of the class. In cancer-associated VTE, ADAM-VTE found significantly less major bleeding than dalteparin, alongside CARAVAGGIO. For gastrointestinal bleeding specifically, Ray (JAMA 2021) found lower bleeding with apixaban than rivaroxaban — in an atrial fibrillation population, so supportive rather than direct VTE evidence.
- After an unprovoked VTE, screen for cancer the ordinary way — and no further. SOME (Carrier, NEJM 2015, Canadian) found that adding routine abdominal-pelvic CT to age-appropriate screening detected no additional cancers. History, examination, basic bloodwork and up-to-date breast, cervical and colorectal screening is the workup.
- Three months is a minimum, not a default answer. What follows depends on the provocation, below.
Duration follows the provocation, so name it explicitly. “Provoked” is not one category — a post-operative clot and a clot on the oral contraceptive pill do not carry the same recurrence risk.
When rivaroxaban can be dose-reduced. The rules differ by indication, which is exactly where the error happens.
- Treatment of VTE: 15 mg BID with food for 21 days, then 20 mg once daily with food.
- Extended treatment beyond 6 months: 10 mg once daily (EINSTEIN-CHOICE, NEJM 2017), once the goal has shifted from treating this clot to preventing the next one.
- Do not carry the atrial fibrillation renal rule across. The AF and VTE indications use different thresholds, and applying the AF reduction to a VTE patient under-doses them.
- Apixaban has the equivalent step down — 2.5 mg BID after 6 months. See the AF post for DOAC pharmacology and bleeding risk in general.
Pre-operative planning — previous VTE, already anticoagulated
Two separate questions, routinely merged into one: when do I stop it, and do I bridge.
- How long ago was the VTE? This dominates everything else. Within 3 months the thrombotic risk is high, and the first question becomes whether elective surgery can simply be deferred.
- DOACs — interrupt by a schedule, do not bridge. PAUSE (Douketis, JAMA Intern Med 2019, Canadian) validated stopping based on renal function and the bleeding risk of the procedure, with no heparin bridging and no pre-operative testing. Note the evidence was generated in atrial fibrillation patients — applying it to VTE is a reasonable extrapolation, not a trial result.
- Warfarin — bridging is usually unnecessary. BRIDGE (NEJM 2015) showed no benefit for most patients. Reserve LMWH bridging for VTE within 3 months or high-risk thrombophilia.
- If surgery cannot wait. Truly urgent surgery within 3 months of a VTE is the high-risk scenario. Discuss with thrombosis or haematology rather than deciding alone; keep the interruption as short as the procedure allows, consider bridging with therapeutic LMWH in the highest-risk window, and reserve a retrievable inferior vena cava filter for the patient whose VTE is within roughly a month and who genuinely cannot be anticoagulated at all — with a documented plan and date for removal, because unretrieved filters cause their own complications.
- Restarting is driven by bleeding risk, not the calendar. Resume once hemostasis is secure — typically 24 hours after low-bleeding-risk surgery, 48–72 hours after high-risk.
- Confirm the specifics against the Thrombosis Canada perioperative guide before you act on memory.
A negative D-dimer only means something if you scored the patient first. In the group where PE is likely, a D-dimer below 500 does not exclude it — and that is exactly the patient in whom false reassurance is most costly. Ordering the test before the score does not merely waste it; it invites you to trust a number that was never going to be interpretable.
Trial Files
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4. Risk Stratification and High-Risk PE
Once PE is confirmed, the next question is not “which anticoagulant” but how sick is this patient. Blood pressure answers it first; the echocardiogram and troponin answer it second. Clot position does not answer it at all — “saddle” is a description, not a risk category.
The three tiers
sPESI — age >80, cancer, chronic cardiopulmonary disease, heart rate ≥110, systolic BP <100 mmHg, SaO2 <90%. Any one point means not low risk.
Intermediate risk — what monitoring actually means
- Continuous cardiac and oximetry monitoring, blood pressure at least hourly for the first 6–12 hours, and a repeat troponin. Deterioration here is gradual and then sudden.
- Escalate on: systolic pressure below 90 mmHg or a fall of 40 mmHg from baseline, a rising heart rate with a falling pressure, a new oxygen requirement, or new confusion. Any of those starts the rescue-thrombolysis conversation — early, not at the arrest.
High-risk PE
Obstructive shock from a right ventricle that cannot overcome the sudden afterload. The RV dilates, its own coronary perfusion falls, and the spiral to arrest can be quick — which is why fluids must be given cautiously. A litre into a failing right ventricle can make the obstruction worse.
- Alteplase 100 mg IV over 2 hours, or an accelerated 0.6 mg/kg over 15 minutes (maximum 50 mg) in arrest or peri-arrest. Decide before the arrest — thrombolysis during CPR is a rescue, not a plan.
- Absolute contraindications: prior intracranial hemorrhage, known structural cerebral vascular lesion or malignancy, ischemic stroke within 3 months, active bleeding, recent head trauma or neurosurgery.
- Catheter-directed therapy or embolectomy where thrombolysis is contraindicated or has failed. Find out what your centre offers before you need it at 3 a.m.
- Call early — critical care, and the local PE response pathway if one exists.
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5. PE in Pregnancy
Pregnancy changes every step of the pathway, so none of the usual shortcuts hold.
- D-dimer rises physiologically through pregnancy and cannot be interpreted against the usual cut-off.
- Use the pregnancy-adapted YEARS algorithm (van der Pol, NEJM 2019): with none of its three criteria and a D-dimer below 1000 µg/L, PE is excluded without imaging.
- Clinical signs of DVT? Scan the leg first. That is the first YEARS criterion, and it changes the test: compression ultrasound before chest imaging, because a proximal DVT is treated exactly as PE is — a positive scan confirms VTE and the chest is never imaged. Without leg symptoms the branch does not open.
- Imaging is still safe when indicated. Both CTPA and V/Q deliver fetal doses well below the threshold of concern — V/Q gives less breast radiation, CTPA less to the fetus. Do not let radiation fear delay a diagnosis that kills.
- Treat with low-molecular-weight heparin. DOACs cross the placenta and are contraindicated; warfarin is teratogenic. Continue at least 6 weeks postpartum and for a minimum of 3 months total.
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Test Yourself
Click on your answer to reveal the explanation.
A 55-year-old man is on the ward four days after an elective hip replacement when he develops sudden breathlessness. Heart rate 112 beats/min, blood pressure 130/80 mmHg and stable, respiratory rate 24 breaths/min, SpO2 92% on room air. His right calf is swollen and tender. His Wells score is 9 — PE likely. The D-dimer comes back at 420 µg/L, below the laboratory cut-off of 500.
What is the most appropriate next step?
A 58-year-old man is admitted with a confirmed segmental PE. He is alert and comfortable at rest. Blood pressure 126/74 mmHg and stable with no vasopressor requirement, heart rate 96 beats/min, SpO2 94% on 2 L by nasal prongs. The CT report notes right ventricular dilatation with an RV/LV ratio of 1.2, and his troponin is elevated. Creatinine and hemoglobin are normal.
How should he be managed?
Reflect
An abdominal CT ordered to investigate weight loss in a 71-year-old woman reports, in its final line, “incidental subsegmental pulmonary emboli in the right lower lobe” — that is, in the small distal branches. She has no chest symptoms and is haemodynamically well. It is 9 p.m., you are covering overnight, and the day team has gone home. What do you do with this finding, and how do you hand it over?
Please do not include patient identifying details — no names, initials, dates, medical record numbers, or any detail that could identify a specific patient or encounter. Write about your reasoning, not about a real person.
Further Reading
- Canadian GuidelineThrombosis Canada Clinical Guides — VTE diagnosis, treatment and perioperative management
- Landmark TrialPEGeD: D-Dimer Adjusted to Clinical Probability — Kearon et al, NEJM 2019
- Landmark TrialPregnancy-Adapted YEARS Algorithm — van der Pol et al, NEJM 2019
- Landmark TrialCARAVAGGIO: Apixaban for Cancer-Associated VTE — Agnelli et al, NEJM 2020
- Landmark TrialPAUSE: Perioperative DOAC Management — Douketis et al, JAMA Intern Med 2019
Week 2