Respiratory

Pulmonary Embolism

A venous clot, usually from a deep leg or pelvic vein, lodges in the pulmonary arterial tree, obstructing perfusion and abruptly loading the right ventricle.

In a nutshell

Pulmonary embolism is a venous clot obstructing the pulmonary arteries, and severity is set by the right ventricle, not the oxygen saturation. Score with two-level PE Wells, then anticoagulate: apixaban 10 mg by mouth twice daily for 7 days, then 5 mg twice daily.

Classic presentation

A patient two weeks after hip replacement with sudden pleuritic chest pain, breathlessness, a heart rate of 110 and a swollen tender calf.

Key points

Wells points: DVT signs 3, alternative diagnosis less likely 3, heart rate over 100 1.5, immobility or recent surgery 1.5, previous VTE 1.5, haemoptysis 1, malignancy 1.
NICE recommends considering an age-adjusted D-dimer threshold in people aged over 50 but publishes no formula. Use the local laboratory's age-adjusted cut-off.
Provoked means a transient major risk factor within 3 months: surgery, trauma, significant immobility, pregnancy, puerperium or hormonal therapy. Anything else is unprovoked.
Active cancer means active antimitotic treatment, diagnosis within 6 months, or recurrent, metastatic or inoperable disease. Squamous skin cancer and basal cell carcinoma do not count.
After an unprovoked PE, review the history, baseline bloods and examination. Do not investigate further for cancer unless symptoms or signs point somewhere.
Do not offer thrombophilia testing after a provoked PE, or to anyone continuing anticoagulation. Antiphospholipid antibody testing is different and may be considered.
Unfractionated heparin with a vitamin K antagonist is not routine treatment. Reserve it for renal impairment, established renal failure or an increased bleeding risk.
A simplified Pulmonary Embolism Severity Index (sPESI) of 0 predicts low 30-day mortality. NICE asks for a validated tool before outpatient treatment but names none.
In pregnancy, heparin and warfarin are both compatible with breastfeeding. Avoid oestrogen-containing contraception afterwards.

First-line investigation

Two-level PE Wells score: more than 4 points means PE likely and immediate CTPA (computed tomography pulmonary angiogram); 4 points or less means D-dimer first.

Management

Stabilise and grade the danger

ABCDE (airway, breathing, circulation, disability, exposure), monitoring and senior help. Oxygen to a target saturation of 94 to 98%, or 88 to 92% if at risk of hypercapnic respiratory failure.⁴
High-risk PE is cardiac arrest, obstructive shock, or systolic blood pressure below 90 mmHg (or a 40 mmHg fall) for over 15 minutes. Call critical care.²

Choose the diagnostic pathway

Two-level PE Wells score first. More than 4 points: CTPA immediately. 4 points or less: D-dimer, aiming for a result within 4 hours.¹
V/Q SPECT (ventilation/perfusion single photon emission computed tomography), or planar V/Q, replaces CTPA for contrast allergy, creatinine clearance under 30 mL/minute, or high irradiation risk.¹
Send FBC, renal and hepatic function, prothrombin time and APTT (activated partial thromboplastin time). Do not wait for them before the first anticoagulant dose.¹

Anticoagulate without avoidable delay

Apixaban 10 mg by mouth twice daily for 7 days, then 5 mg twice daily. Start it while awaiting imaging or a slow D-dimer.^1,6
Or rivaroxaban 15 mg by mouth twice daily with food for 21 days, then 20 mg once daily with food.^1,7
If neither suits: LMWH (low molecular weight heparin) for at least 5 days, then dabigatran or edoxaban, or LMWH with warfarin to an INR of 2.0 twice.^1,9
Enoxaparin treatment dose is 1.5 mg/kg subcutaneously every 24 hours, or 1 mg/kg every 12 hours with cancer, obesity, symptomatic PE or recurrent VTE.⁸

Reperfuse the unstable patient

Haemodynamic instability: unfractionated heparin 10 000 units intravenously, then 18 units/kg/hour by continuous infusion, titrated to the APTT with laboratory monitoring.^1,10
Consider alteplase 10 mg intravenously over 1 to 2 minutes, then 90 mg by infusion over 2 hours. Maximum 1.5 mg/kg if under 65 kg.^1,11
Do not thrombolyse a stable patient for right-ventricular dysfunction alone. Consider an inferior vena cava filter only if anticoagulation is contraindicated or PE recurs on treatment.¹

Cancer, pregnancy and renal impairment

Active cancer: 3 to 6 months of anticoagulation, reviewed at 3 to 6 months. Consider a DOAC (direct-acting oral anticoagulant), weighing tumour site, interactions and bleeding risk.¹
Pregnancy: NG158 does not apply. Enoxaparin twice daily by booking weight, 40 mg under 50 kg rising to 100 mg at 90 to 109 kg.^5,8
Massive PE in pregnancy: intravenous unfractionated heparin, urgent portable echocardiogram or CTPA within 1 hour, and consider immediate thrombolysis.⁵
Creatinine clearance under 15 mL/minute: LMWH or unfractionated heparin, not a DOAC. Weight below 50 kg or above 120 kg: monitor anticoagulant levels.¹

Duration, review and safe discharge

Treat for at least 3 months. Provoked and the factor has gone: consider stopping. Unprovoked: consider continuing, balancing recurrence against bleeding.¹
In pregnancy, continue until at least 6 weeks after birth and for at least 3 months in total.^5,12
HAS-BLED, a major-bleeding risk score, of 4 or more and unmodifiable: discuss stopping. If anticoagulation is declined, consider aspirin 75 mg or 150 mg daily. Review at least yearly.¹
Outpatient treatment for low-risk PE needs a validated risk tool, an anticoagulant alert card, thrombosis-team contact details and clear return advice.^1,3

Exam traps

A normal chest X-ray and a normal ECG do not exclude PE. The chest X-ray is there to find other causes.
Never send a D-dimer to confirm PE, and never send one in a PE-likely patient. It can only exclude.
D-dimer has no place at all in investigating venous thromboembolism in pregnancy.
PERC (pulmonary embolism rule-out criteria) applies only when suspicion is already low. It is not a universal rule-out, and it is unvalidated in COVID-19.
S1Q3T3, an S wave in lead I with a Q wave and inverted T wave in lead III, is rare. Sinus tachycardia is far commoner.
Right-ventricular dysfunction in a haemodynamically stable patient is not an indication for thrombolysis.
Do not decide on long-term anticoagulation from a prediction tool alone.
An inferior vena cava (IVC) filter is not a substitute for anticoagulation. Agree the removal plan before it goes in.
Direct-acting oral anticoagulants are not recommended in triple positive antiphospholipid syndrome, which raises recurrent thrombosis.

Illustrations

Embolus lodging in the pulmonary arterial treeDiagram showing a thrombus travelling from a deep leg vein through the right heart to occlude a pulmonary artery branch, creating dead space distally.PassFinals · original

CT pulmonary angiogram with filling defectAxial CTPA image showing a dark filling defect within a contrast-opacified pulmonary artery.James Heilman, MD, Wikimedia Commons · CC-BY-SA-4.0

Key sources

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.