NCLEX Review Guide: Pulmonary Embolism

Definition & Etiology

• A pulmonary embolism (PE) is a sudden blockage of a pulmonary artery caused by emboli, most commonly from deep vein thrombosis (DVT) in the lower extremities. The embolus travels through the venous system, through the right side of the heart, and lodges in the pulmonary vasculature.
• Risk factors include Virchow's triad: hypercoagulability (pregnancy, oral contraceptives, malignancy), venous stasis (immobility, surgery), and endothelial injury (trauma, surgery, IV drug use).

Pathophysiological Changes

• When a pulmonary artery becomes occluded, ventilation-perfusion (V/Q) mismatch occurs, leading to hypoxemia. The affected area of the lung is ventilated but not perfused, creating physiologic dead space.
• Pulmonary embolism can lead to increased pulmonary vascular resistance, which can cause right ventricular strain and failure in severe cases. The release of inflammatory mediators can cause bronchoconstriction and further impair gas exchange.

Signs and Symptoms

• Dyspnea is the most common symptom (85% of cases), typically of sudden onset. Other respiratory symptoms include pleuritic chest pain (sharp, worsened by inspiration) and hemoptysis (less common).
• Cardiovascular manifestations include tachycardia, hypotension (in massive PE), and signs of right heart failure such as jugular venous distention and a loud S2 heart sound. Anxiety, syncope, and diaphoresis may also be present.

Severity Classification

• Massive PE: Characterized by sustained hypotension (systolic BP <90 mmHg for >15 minutes), pulselessness, or persistent bradycardia. Associated with right ventricular dysfunction and high mortality.
• Submassive PE: Normotensive but with evidence of right ventricular dysfunction or myocardial necrosis. Low-risk PE: Normotensive with normal right ventricular function and no myocardial necrosis.

Diagnostic Tests

• D-dimer: A sensitive but not specific screening test. A negative D-dimer in a low-risk patient can help rule out PE, but an elevated D-dimer requires further diagnostic imaging.
• CT Pulmonary Angiography (CTPA): The gold standard diagnostic test, which directly visualizes the pulmonary arterial tree and can identify the location and size of emboli. Additional tests include V/Q scan, arterial blood gases, ECG, and echocardiogram.

Laboratory and Other Findings

• ABG findings typically show hypoxemia, hypocapnia, and respiratory alkalosis due to tachypnea. The A-a gradient is usually increased, reflecting V/Q mismatch.
• ECG changes may include sinus tachycardia, S1Q3T3 pattern (S wave in lead I, Q wave in lead III, and inverted T wave in lead III), right bundle branch block, and right axis deviation. Troponin and BNP may be elevated due to right ventricular strain.

Anticoagulation Therapy

• Unfractionated Heparin (UFH): Initial IV bolus followed by continuous infusion, monitored with aPTT. Preferred in massive PE, renal failure, or when rapid reversal may be needed. Protamine sulfate is the antidote.
• Low Molecular Weight Heparin (LMWH): Subcutaneous injection (enoxaparin, dalteparin) with more predictable pharmacokinetics. Direct Oral Anticoagulants (DOACs): Rivaroxaban, apixaban, dabigatran, or edoxaban may be used for initial or long-term treatment. Warfarin: Oral vitamin K antagonist for long-term therapy, requires INR monitoring (target 2-3).

Thrombolytic Therapy

• Thrombolytic agents (alteplase, tenecteplase, reteplase) are reserved for massive PE with hemodynamic instability or right ventricular dysfunction. These medications actively dissolve clots but carry a higher risk of bleeding complications.
• Contraindications include recent surgery, active internal bleeding, history of hemorrhagic stroke, or uncontrolled hypertension. Careful patient selection is critical to balance the benefits against bleeding risks.

Supportive Care

• Oxygen therapy to maintain SpO2 >90%, hemodynamic support with IV fluids, and vasopressors if needed for persistent hypotension. Pain management with analgesics for pleuritic chest pain.
• Mechanical ventilation may be required for respiratory failure. For patients with contraindications to anticoagulation, inferior vena cava (IVC) filters may be placed to prevent further emboli.

Procedure: Oxygen Administration for PE

1. Assess patient's respiratory status, including rate, depth, and oxygen saturation
2. Select appropriate oxygen delivery device based on patient needs (nasal cannula, simple mask, non-rebreather)
3. Start with low-flow oxygen and titrate to maintain SpO2 >90-92%
4. Position patient in high Fowler's or semi-Fowler's position to optimize ventilation
5. Monitor vital signs, oxygen saturation, and work of breathing continuously
6. Assess for signs of respiratory failure requiring escalation to high-flow oxygen or mechanical ventilation
7. Document oxygen flow rate, delivery method, and patient response

Assessment & Monitoring

• Perform frequent respiratory assessments including respiratory rate, depth, pattern, use of accessory muscles, and oxygen saturation. Monitor vital signs, particularly heart rate and blood pressure, to detect early signs of deterioration.
• Assess for signs of bleeding when on anticoagulation therapy. Monitor laboratory values including CBC, coagulation studies (PT/INR, aPTT), and renal function. Continuously evaluate pain levels and response to interventions.

Nursing Interventions

• Administer anticoagulation therapy as prescribed, ensuring proper technique for subcutaneous injections and maintaining accurate IV infusion rates. Provide oxygen therapy and position the patient to optimize ventilation, typically in high Fowler's position.
• Implement DVT prophylaxis measures including early mobilization (when stable), pneumatic compression devices, and graduated compression stockings. Provide patient education regarding medication adherence, signs of bleeding, and when to seek medical attention.

Primary Prevention Strategies

• Mechanical prophylaxis includes early ambulation, graduated compression stockings (applying 30-40 mmHg pressure at the ankle), and intermittent pneumatic compression devices. These methods increase venous return and reduce venous stasis.
• Pharmacological prophylaxis with LMWH, UFH, or fondaparinux is recommended for high-risk patients (major surgery, trauma, prolonged immobility). Risk assessment tools (e.g., Caprini score) help identify patients who would benefit from prophylaxis.

PE vs. Other Cardiopulmonary Conditions

Anticoagulant Medications

Memory Aids

Common Pitfalls

• Misinterpreting normal chest X-rays: A normal chest X-ray does not rule out PE. Many students incorrectly assume that a PE would be visible on a standard chest X-ray, but this is rarely the case.
• Confusing anticoagulation with thrombolysis: Anticoagulants prevent new clot formation but do not dissolve existing clots. Thrombolytics actively break down clots but carry higher bleeding risks.
• Overlooking PE in patients with COPD exacerbations: PE can mimic or trigger COPD exacerbations, leading to delayed diagnosis. Always consider PE in patients with risk factors who present with worsening respiratory symptoms.

NCLEX Practice Approach

• For PE questions, prioritize oxygenation and hemodynamic stability in your answers. Remember that PE is a potentially life-threatening condition, so answers that address immediate physiological needs take precedence.
• When presented with lab values, look for hypoxemia (decreased PaO2), respiratory alkalosis (decreased PaCO2, increased pH), and increased A-a gradient as classic findings in PE.
• For medication questions, understand the differences between anticoagulants and their monitoring requirements. Know that bridging therapy (heparin to warfarin) is necessary due to warfarin's delayed onset and initial procoagulant effect.