Pulmonary Embolism

Life-Threatening PE and CEN Exam Priorities

Pulmonary embolism (PE) is a life-threatening respiratory emergency caused by the sudden occlusion of one or more pulmonary arteries, most often by a thrombus originating from the deep veins of the lower extremities. In the emergency department, PE is a high-acuity, time-sensitive diagnosis that requires rapid recognition, risk stratification, and intervention to reduce morbidity and mortality. For the CEN exam, mastery of PE presentation, diagnostic workup, and evidence-based management is essential, as this topic appears frequently in both adult and geriatric patient scenarios.^[1]^[2]

PE Terminology and Severity Classification

Pulmonary Embolism (PE): Occlusion of one or more pulmonary arteries by a thrombus, air, fat, or amniotic fluid. The most common cause is deep vein thrombosis (DVT).
Thromboembolism: A blood clot that forms in a vein (usually in the leg or pelvis) and travels to the pulmonary circulation.
Massive PE: PE with sustained hypotension (SBP <90 mmHg for >15 minutes) or requiring inotropic support; carries a high risk of obstructive shock and death.^[3]
Submassive PE: PE with evidence of right ventricular (RV) strain on imaging or elevated biomarkers (e.g., troponin, BNP) but without hypotension.
Low-risk PE: Hemodynamically stable, no RV strain, normal biomarkers; often managed with anticoagulation alone.
Virchow's Triad — the three factors that predispose to venous thromboembolism: venous stasis, endothelial injury, and hypercoagulability.

Thrombus Cascade and Right Ventricular Failure

3.1 Pathophysiologic Cascade

A thrombus forms in a deep vein (usually in the lower extremity or pelvis).
The thrombus dislodges and travels through the right heart into the pulmonary arterial circulation.
The embolus lodges in a pulmonary artery branch, causing mechanical obstruction to blood flow.
Obstruction increases pulmonary vascular resistance (PVR), leading to right ventricular afterload.
Right ventricle (RV) dilates and fails → decreased LV preload → decreased cardiac output → hypotension and shock.
Ventilation-perfusion (V/Q) mismatch occurs: ventilated alveoli are not perfused → hypoxemia.
Release of inflammatory mediators and vasoactive substances worsens pulmonary vasoconstriction and edema.^[4]

3.2 Key Clinical Correlation

The severity of PE depends on the size and location of the embolus, the patient's cardiopulmonary reserve, and the degree of RV adaptation. A large, centrally located embolus (saddle embolus) can cause obstructive shock and cardiac arrest.^[5]

Recognizing PE in Emergency Presentations

Sudden-onset dyspnea — most common symptom (present in >80% of cases).
Pleuritic chest pain — sharp, worse with inspiration; may mimic pericarditis or pneumonia.
Tachypnea — respiratory rate >20/min (very sensitive but not specific).
Tachycardia — early sign of hemodynamic stress.
Hemoptysis — suggests pulmonary infarction; less common.
Syncope or near-syncope — indicates massive PE or significant RV compromise.
Hypotension — ominous sign; indicates massive PE.
Signs of DVT — unilateral leg swelling, warmth, erythema, or palpable cord.
Anxiety, diaphoresis, and sense of impending doom.
Jugular venous distention (JVD) — reflects elevated right-sided heart pressures.
Lung exam may be normal, or may reveal focal wheezing, crackles, or a pleural rub.

➡ On the CEN exam, remember that the classic triad of PE is dyspnea, chest pain, and hemoptysis, but most patients present with only dyspnea and tachypnea.^[1]^[6]

Risk Stratification and Diagnostic Workup

5.1 Risk Stratification Tools

Wells Criteria for PE — pre-test probability scoring based on clinical signs, symptoms, and risk factors (e.g., prior DVT/PE, hemoptysis, malignancy, heart rate >100). Scores stratify patients into low, moderate, or high probability.^[7]
Revised Geneva Score — another validated clinical prediction rule; less subjective than Wells.
PERC Rule — for low-probability patients: if PERC negative (no criteria present), D-dimer testing may be safely deferred.

5.2 Diagnostic Testing

D-dimer (high sensitivity ELISA): Elevated in acute thrombosis, but non-specific. A negative D-dimer essentially rules out PE in low- or moderate-risk patients.^[8]
CT Pulmonary Angiography (CTPA): Gold standard imaging study; visualizes clot in pulmonary arteries. Requires IV contrast.
Ventilation-Perfusion (V/Q) Scan: Alternative for patients with contraindications to contrast (e.g., renal impairment, contrast allergy). Less specific than CTPA.
ECG: Often shows sinus tachycardia; may show S₁Q₃T₃ pattern (S wave in lead I, Q wave in lead III, inverted T wave in lead III) — classic but low sensitivity. Also look for right axis deviation, RBBB, or atrial fibrillation.^[9]
Chest X-ray: Can be normal; may show atelectasis, pleural effusion, or a Hampton's hump (wedge-shaped opacity indicating infarction).
Bedside Echocardiography (ECHO): Useful for assessing RV strain, RV dilation, and McConnell's sign (hypokinesis of the RV free wall with apical sparing). Findings help risk-stratify for massive vs. submassive PE.^[3]
Arterial Blood Gas (ABG): May show respiratory alkalosis, hypoxemia, and an increased A-a gradient.

5.3 Key Exam Points for Diagnosis

In hemodynamically unstable patients, bedside ECHO is often the quickest way to confirm RV strain and guide emergent treatment.
In stable patients, CTPA is the imaging study of choice.
D-dimer is most useful in low- to moderate-risk patients; it should not be used in high-risk patients (go straight to CTPA).^[8]

Anticoagulation, Thrombolysis, and Nursing Care

6.1 Emergency Department Management

Airway, Breathing, Circulation (ABCs): Administer high-flow oxygen via non-rebreather mask. Prepare for intubation if respiratory failure develops.
Hemodynamic support: IV fluids (cautiously, as excessive fluids can worsen RV failure). Start norepinephrine or vasopressin for hypotension.
Anticoagulation: Initiate immediately once PE is confirmed or strongly suspected.^[10]
- Unfractionated heparin (UFH): Bolus 80 units/kg, then 18 units/kg/hr (titrate to PTT 60–80 sec). Preferred in massive PE and if thrombolysis is anticipated.
- Low molecular weight heparin (LMWH): Enoxaparin 1 mg/kg SC q12h (for stable, low-risk patients).
- Direct oral anticoagulants (DOACs): Rivaroxaban, apixaban, or edoxaban for stable patients without severe renal impairment.
Thrombolytic therapy (fibrinolysis): Indicated for massive PE with obstructive shock or cardiac arrest. Use alteplase (tPA) 100 mg IV over 2 hours (or 50 mg IV push in cardiac arrest).^[3]^[11]
Embolectomy (surgical or catheter-directed): Consider for patients with massive PE who have contraindications to fibrinolytics or fail thrombolysis.^[12]
IVC filter placement: Consider if there is a contraindication to anticoagulation (e.g., active bleeding) or recurrent PE on adequate therapy.

6.2 Nursing Interventions and Monitoring

Continuous cardiac monitoring for dysrhythmias and signs of RV strain.
Frequent vital signs including blood pressure, heart rate, respiratory rate, and SpO₂.
Monitor for bleeding complications from anticoagulation or thrombolysis (e.g., intracranial hemorrhage, retroperitoneal bleed).
Prepare for emergent transvenous pacing or CPR if patient deteriorates.
Administer pain management for pleuritic chest pain (avoid NSAIDs if anticoagulated).
Provide emotional support and explain all procedures to the patient and family.^[13]

Critical Warnings and Complication Avoidance

7.1 Key Safety Warnings

Do not delay anticoagulation in high-probability PE pending confirmatory imaging if the patient is unstable — clinical judgment supersedes test results.
Avoid liberal IV fluids in massive PE: over-resuscitation worsens RV failure by causing further RV dilation and septal bowing.
When using thrombolytics, monitor for signs of intracranial hemorrhage (sudden severe headache, altered mental status, neurological deficits).
IVC filters carry a risk of filter migration, thrombosis, and perforation; they reduce the risk of PE but do not treat the DVT itself.

7.2 Common Complications

Obstructive shock — leading cause of death in massive PE.
Cardiac arrest — often pulseless electrical activity (PEA) due to RV outflow obstruction.
Right ventricular infarction — increased wall stress can cause RV ischemia.
Pulmonary infarction — necrosis of lung tissue distal to the clot; can cause hemoptysis and fever.
Paradoxical embolism — clot crosses a patent foramen ovale (PFO) causing systemic arterial embolism (e.g., stroke).
Recurrent PE — more likely if anticoagulation is inadequate or underlying hypercoagulable state is not addressed.^[14]

CEN Exam Essentials and Memory Aids

🔑 Most common ECG finding in PE = sinus tachycardia. S₁Q₃T₃ is classic but present in only ~20% of cases.
🔑 Most sensitive indicator of PE = elevated D-dimer. Most specific test = CTPA.
🔑 Massive PE = hypotension + RV strain → treat with thrombolytics. Submassive PE = RV strain but stable BP → anticoagulate and monitor.
🔑 McConnell's sign on ECHO: RV free wall hypokinesis with apical sparing — highly suggestive of PE.
🔑 Remember the PERC rule: Age >50, HR >100, SpO₂ <95%, prior DVT/PE, surgery, hemoptysis, estrogen use, unilateral leg swelling. If all negative (PERC negative), no D-dimer or CTPA needed in low-risk patients.^[8]
🔑 Heparin + warfarin overlap for 5 days (until INR 2–3) is the traditional approach for stable PE; many now use DOACs as first-line therapy.
🔑 For the CEN exam, know the S₁Q₃T₃ pattern and that it represents acute right heart strain — not specific to PE but a high-yield board question.
🔑 Nursing pearl: If a patient with PE suddenly deteriorates after starting anticoagulation, consider heparin-induced thrombocytopenia (HIT) or recurrent PE.

Memory Aid — "PE is a Block"

Letter	What to Remember	Clinical Action
P	Pain (pleuritic), Pressure (RV afterload)	Oxygen, monitor vitals
E	Embolus (clot), ECG changes, ECHO evaluation	CTPA or V/Q, ECHO
B	Blocked vessel, Breathing difficulty	Anticoagulation ± thrombolysis
L	Low cardiac output, Leg swelling (DVT)	IVC filter if contraindication to anticoagulation
O	Obstructive shock, Oxygen desaturation	Prepare for embolectomy or CPR
C	Clot, Cardiac arrest (PEA)	tPA in cardiac arrest
K	Knowledge of well's criteria, Kill the clot	Risk stratify, treat early