Pulmonology

Pulmonary Embolism (PE)

Respiratory-focused PE overview with severity triage, anticoagulation selection, thrombolysis decision points, and duration planning.

Typical Source
Lower-extremity DVT
Massive PE
Hypotension or shock
Stable PE
DOAC preferred
Minimum Duration
3 months

PE Risk Stratification and Treatment Trigger Map

Massive PE Hypotension / shock Consider thrombolysis Submassive PE RV dysfunction / troponin+ Escalated monitoring Low Risk PE Hemodynamically stable Anticoagulation first Initiate anticoagulation early when suspicion is high and bleeding risk is acceptable Choose UFH/LMWH/DOAC based on stability, renal function, and bleeding profile

1. Definition

Pulmonary embolism is obstruction of the pulmonary arterial circulation, most often due to thrombus migration from lower-extremity DVT.

2. Clinical Presentation

Common

  • Sudden dyspnea
  • Pleuritic chest pain
  • Tachycardia
  • Hypoxia

Severe

  • Hypotension
  • Shock

3. Risk Stratification

Massive: hypotension / shock Submassive: RV dysfunction + troponin elevation Low-risk: stable hemodynamics
Severity category drives urgency and whether thrombolysis is indicated.

4. Initial Anticoagulation

Start promptly when PE is suspected and bleeding risk is acceptable.

Agent MOA Dose Monitoring Contraindications
Unfractionated heparin (UFH) Antithrombin activation; inhibits thrombin (IIa) and Xa 80 units/kg IV bolus, then 18 units/kg/hour infusion aPTT target about 1.5 to 2.5x control Active major bleeding, prior HIT
Enoxaparin (LMWH) Predominantly inhibits factor Xa 1 mg/kg SC every 12 hours OR 1.5 mg/kg once daily Clinical bleeding surveillance; renal function; anti-Xa in select high-risk settings Active bleeding, history of HIT (use caution), severe renal dysfunction without adjustment

UFH Preferred When

  • Severe renal impairment
  • High bleeding concern (short half-life and reversibility)

Shared Risks

  • Bleeding
  • HIT risk (lower with LMWH than UFH)

5. Direct Oral Anticoagulants (DOACs)

Preferred for most hemodynamically stable PE patients.

Agent MOA Dose Monitoring Contraindications
Apixaban Direct factor Xa inhibitor 10 mg BID for 7 days, then 5 mg BID; extended prevention 2.5 mg BID No routine coagulation monitoring; monitor renal/hepatic function and bleeding Active bleeding, severe renal failure, major hepatic disease with coagulopathy
Rivaroxaban Direct factor Xa inhibitor 15 mg BID for 21 days, then 20 mg once daily No routine coagulation monitoring; monitor renal/hepatic function and bleeding Active bleeding, severe renal failure, major hepatic disease with coagulopathy
Main advantage: fixed dosing without routine lab anticoagulation checks.

6. Thrombolysis (Massive PE Only)

Alteplase (tPA)

  • MOA: converts plasminogen to plasmin for fibrin clot lysis
  • Dose: 100 mg IV over 2 hours
  • Monitoring: hemodynamics, bleeding signs, neurologic status
  • Contraindications: active bleeding, recent stroke, recent major surgery
Reserve for hemodynamic instability due to substantial bleeding risk.

7. Duration of Anticoagulation

Provoked PE

  • Typically 3 months

Unprovoked PE

  • At least 3 months, then reassess for indefinite treatment

Cancer-Associated PE

  • DOAC often preferred unless bleeding profile suggests otherwise

8. Inferior Vena Cava (IVC) Filter

  • Use when there is an absolute contraindication to anticoagulation
  • Remove when anticoagulation can be safely initiated

Management Recap Drill

Stable PE: start DOAC in most cases.
Severe renal impairment: prefer UFH.
Massive PE: evaluate for thrombolysis.
Duration anchor: minimum 3 months.

PE Treatment Flow

Suspected / confirmed PE Assess bleeding + stability Hemodynamically stable DOAC or heparin pathway Shock / hypotension Massive PE, consider tPA Continue anticoagulation and plan duration by provoked/unprovoked/cancer context Reassess bleeding risk periodically throughout therapy

Guideline References (Management)

CHEST Guidance

https://www.chestnet.org

ESC PE Guidance

European Society of Cardiology pulmonary embolism guidance

DOAC dosing Thrombolysis criteria Duration recommendations

9. Common Exam Traps

Apixaban initial loading: 10 mg BID for 7 days.
Rivaroxaban initial phase: 15 mg BID for 21 days.
Massive PE with instability can warrant thrombolysis.
IVC filter is for anticoagulation contraindication, not routine use.
Stable PE generally favors DOAC-based treatment.

10. Quick Revision Summary

Must Remember

  • Most PE events originate from DVT
  • DOAC first-line for most stable patients
  • UFH is useful in severe renal failure or unstable contexts
  • tPA is reserved for hemodynamic compromise
  • Minimum anticoagulation duration is usually 3 months

High-Yield Subtopics

  • DOAC loading and maintenance dose transitions
  • UFH infusion and aPTT adjustment logic
  • Thrombolysis indications and contraindications
  • Provoked vs unprovoked duration decisions

Practice Questions

1) What loading schedule is used for apixaban in acute PE?

Answer: 10 mg twice daily for 7 days, then 5 mg twice daily.

2) Which anticoagulant is often preferred in severe renal impairment?

Answer: UFH, because it is short-acting, reversible, and easier to titrate with aPTT.

3) What is the standard rivaroxaban transition schedule in PE?

Answer: 15 mg twice daily for 21 days, then 20 mg once daily.

4) When is systemic thrombolysis most appropriate in PE?

Answer: Massive PE with hemodynamic instability (for example hypotension/shock), if no major contraindication.

5) What is the typical minimum duration of anticoagulation after PE?

Answer: At least 3 months, then extended based on recurrence and bleeding risk profile.