Pulmonary Embolism in the ICU — Structured Guide

🫀 1 · Overview

Pulmonary embolism

"PE kills through acute right-ventricular failure: a clot obstructs the pulmonary circulation, RV afterload rises abruptly, and a thin-walled RV dilates and fails. Everything — the risk score, the imaging, the decision to lyse — is a way of asking one question: is the right ventricle coping?"

Summarised from Irwin & Rippe's Intensive Care Medicine; with Marino's The ICU Book, Oh's Intensive Care Manual and ESC.

PE is the pulmonary end of venous thromboembolism (VTE) (with DVT). Most ICU patients are at high VTE risk; more than half of fatal PEs were never suspected — so the diagnosis is the hard part.

🎯 2 · Risk Factors (Virchow)

Who clots

Stasis	Endothelial injury	Hypercoagulability
Immobility, ICU stay	Surgery, trauma	Malignancy
Long travel, paresis	Central venous catheters	Pregnancy/puerperium, oestrogens
Heart failure	Prior DVT	Sepsis, inherited thrombophilia, antiphospholipid

Thrombophilia is present in up to half of young/idiopathic VTE, but screening rarely changes acute management — treat the clot, defer thrombophilia work-up.

🚦 3 · Risk Stratification (ESC)

Is the RV coping? — this decides treatment

Category	Haemodynamics	RV dysfunction (imaging)	Troponin
High-risk (massive)	Shock / persistent hypotension / arrest	Yes	Usually +
Intermediate-high	Stable	Yes	+
Intermediate-low	Stable	One or neither of RV dysfunction / troponin	±
Low-risk	Stable	No (sPESI 0)	−

Definitions you must know

Haemodynamic instability = cardiac arrest, obstructive shock (SBP <90 or vasopressors + hypoperfusion), or persistent hypotension (SBP <90 or a drop ≥40 mmHg for >15 min).
sPESI (each 1 point): age >80, cancer, chronic cardiopulmonary disease, HR ≥110, SBP <100, SpO₂ <90%. Score 0 = low risk.

🩺 4 · Diagnosis

Confirm it — pathway depends on stability

Unstable (suspected high-risk)

Don't wait for CT — bedside echo: RV dilatation/strain supports the diagnosis and justifies reperfusion. CTPA as soon as safe.

Stable

Wells / Geneva pre-test probability → if unlikely, D-dimer (age-adjusted) to rule out; if likely or D-dimer positive → CTPA (V/Q if contrast contraindicated).

Supporting tests

ECG (sinus tachy, S1Q3T3, RV strain), ABG (hypoxaemia, ↑ A–a), troponin/BNP (RV strain), leg compression ultrasound (DVT).

💉 5 · Management by Category

Treat to the risk

Category	Treatment
High-risk (shock)	Systemic thrombolysis (e.g. alteplase) unless contraindicated; if contraindicated/failed → catheter-directed therapy or surgical embolectomy. Support: cautious fluids, noradrenaline ± inotrope, O₂; ECMO as a bridge in extremis.
Intermediate-high	Anticoagulate + monitor closely; rescue thrombolysis (or catheter therapy) if they deteriorate. Not routine full-dose lysis.
Intermediate-low	Anticoagulation; admit/observe.
Low-risk	Anticoagulation; consider early discharge/outpatient (Hestia/sPESI 0).

⚠️ The RV-failure trap at intubation

Positive-pressure ventilation and induction agents can collapse a failing RV. Avoid intubation if possible; if unavoidable, optimise preload/pressor first, use gentle settings, and avoid fluid overload (a distended RV worsens by bowing the septum).

💊 6 · Anticoagulation

The backbone of every category

Agent	Use	Note
DOAC (apixaban, rivaroxaban)	First line for most	Single-drug; edoxaban/dabigatran need LMWH lead-in
LMWH	Cancer, pregnancy, initial therapy	Renally cleared; weight-based
UFH infusion	High-risk/unstable, severe renal failure, planned lysis	Titratable, rapidly reversible
Warfarin	Antiphospholipid syndrome, valves	Overlap with heparin until INR therapeutic

Duration: provoked by a transient factor → ~3 months; unprovoked, recurrent or ongoing risk (cancer, thrombophilia) → extended/indefinite, reassessing bleeding risk.

🧩 7 · Special Situations

Adjuncts & caveats

IVC filter: only when anticoagulation is contraindicated or PE recurs despite adequate anticoagulation — not routine.
Cancer-associated VTE: DOAC or LMWH; watch GI/GU bleeding with DOACs.
Pregnancy: LMWH (avoid DOAC/warfarin); tailored diagnostic pathway.
Prophylaxis: almost all ICU patients need pharmacological or mechanical VTE prophylaxis — prevention beats treatment.

🚫 8 · Common Mistakes

Common mistakes

❌ 1 — Large fluid boluses in RV failure

Over-filling a strained RV worsens septal bowing and cardiac output. Give small, cautious challenges and start noradrenaline early.

❌ 2 — Waiting for CT in the crashing patient

Use bedside echo — RV strain justifies reperfusion when CT isn't safe.

❌ 3 — Routine lysis of all intermediate-risk PE

Full-dose lysis in stable intermediate-high PE increases bleeding — anticoagulate and watch, lyse only if they deteriorate.

❌ 4 — D-dimer in high pre-test probability

A negative D-dimer does not exclude PE when probability is high — go to imaging.

❌ 5 — Forgetting prophylaxis

Most fatal PEs are unsuspected — VTE prophylaxis for nearly every ICU patient.

🎓 9 · Exam Pearls — DrNB / IDCCM / IFCCM

Exam pearls

Q: Define high-risk PE.
PE with haemodynamic instability — cardiac arrest, obstructive shock, or persistent hypotension — regardless of the imaging.

Q: Intermediate-high vs intermediate-low?
Both stable; intermediate-high has both RV dysfunction on imaging and raised troponin.

Q: When do you thrombolyse?
High-risk PE (shock) unless contraindicated; as rescue in intermediate-high PE that deteriorates.

Q: First-line anticoagulant?
A DOAC for most; UFH infusion if unstable/renal failure/planned lysis; LMWH in cancer/pregnancy.

Q: When is an IVC filter indicated?
Anticoagulation contraindicated, or recurrent PE despite adequate anticoagulation.

⭐ 10 · Key Differences

All the comparisons in one place

The distinctions that decide reperfusion and answers — gathered at the end.

High vs Intermediate vs Low-risk PE

Feature	High-risk	Intermediate	Low-risk
Haemodynamics	Unstable / shock	Stable	Stable
RV dysfunction	Yes	±	No
Treatment	Thrombolysis / embolectomy	Anticoagulate ± rescue lysis	Anticoagulate ± early discharge

Thrombolysis vs Anticoagulation

Feature	Thrombolysis	Anticoagulation
Action	Actively dissolves clot	Prevents propagation; body lyses over time
Speed	Rapid RV unloading	Gradual
Main risk	Major/intracranial bleeding	Bleeding (lower)
Indication	High-risk (shock); rescue	All PE — the backbone

CTPA vs V/Q scan

Feature	CTPA	V/Q scan
Availability/speed	Fast, first-line	Slower, limited hours
Best when	Most patients	Contrast allergy, renal failure, pregnancy (low radiation to breast), normal CXR
Extras	Alternative diagnoses, RV size	No alternative diagnosis

📚 11 · References

References

Irwin RS, Lilly CM, Mayo PH, Rippe JM (eds). Irwin & Rippe's Intensive Care Medicine. 9th ed. Wolters Kluwer; 2023.
Marino PL. Marino's The ICU Book. 5th ed. Wolters Kluwer; 2025.
Bersten AD, Handy JM (eds). Oh's Intensive Care Manual. Elsevier; 2026.
Konstantinides SV, Meyer G, Becattini C, et al. 2019 ESC Guidelines for the diagnosis and management of acute pulmonary embolism. Eur Heart J. 2020;41:543–603.
Meyer G, Vicaut E, Danays T, et al. (PEITHO). Fibrinolysis for intermediate-risk pulmonary embolism. N Engl J Med. 2014;370:1402–1411.
Stevens SM, Woller SC, Kreuziger LB, et al. Antithrombotic therapy for VTE disease: CHEST guideline. Chest. 2021;160:e545–e608.