How to Assess Pretest Probability and Key History

Show Notes

Core Concepts and Initial Approach

• Definition: Obstruction of pulmonary arteries, usually from a DVT in the proximal lower extremity veins (iliac/femoral), but may be tumor, air, or fat emboli.
• Incidence & Mortality: 300,000–370,000 cases/year in the USA, with 60,000–100,000 deaths annually.
• Mantra: “Don’t anchor on the obvious. Always risk stratify and resuscitate with precision.”
• Risk Factors: Broad, including older age, inherited thrombophilias, malignancy, recent surgery/trauma, travel, smoking, hormonal use, and pregnancy.

Clinical Presentation and Risk Stratification

• Presentation: Highly variable, showing up as anything from subtle shortness of breath to collapse.
• Acute/Subacute: Dyspnea (most common), pleuritic chest pain, cough, hemoptysis, and syncope. Patients are likely tachycardic, tachypneic, hypoxemic on room air, and may have a low-grade fever.
• Chronic: Can mimic acute symptoms or be totally asymptomatic.
• Pulmonary Infarction Signs: Pleuritic pain, hemoptysis, and an effusion.
• High-Risk Red Flags: Signs of hypotension (systolic blood pressure < 90 mmHg for over 15 minutes), requirement of vasopressors, or signs of shock → activate PERT team immediately.
• Crucial Mimics: Think broadly; consider pneumonia, ACS, pneumothorax, heart failure exacerbation, and aortic dissection.

Workup & Diagnostics

• History/Scoring: Ask about prior clots, recent surgeries, hospitalizations, travel. Use Wells/PERC criteria to assess pretest probability.
• Labs:
  • D-dimer: A good test to rule out PE in a patient with low probability. If suspicion is high, proceed directly to imaging.
  • Troponin/BNP: Act as RV stress gauges. Elevated levels are associated with increased risk of a complicated clinical course (25-40%).
  • Lactate: Helpful in identifying patients in possible cardiogenic shock.
  • EKG: Most common finding is sinus tachycardia. Classic RV strain patterns (S₁Q₃T₃, T-wave changes/inversions) are nonspecific.
• Imaging:
  • CXR: Usually normal, but quick and essential to rule out other causes.
  • CTPA: The usual standard and gold standard for stable patients. High sensitivity (> 95%) and can detect RV enlargement/strain.
  • V/Q Scan: Option for patients with contraindications to contrast (e.g., severe contrast allergies).
  • POCUS (Point-of-Care Ultrasound): Useful adjunct for unstable patients.
    • Bedside Echo: Can show signs of RV strain (enlarged RV, McConnell sign).
    • Lower Extremity Ultrasound: Can identify a DVT in proximal leg veins.

Treatment & Management

• Resuscitation (Reviving the RV):
  • Oxygenation: Give supplementally as needed (nasal cannula, non-rebreather, high flow).
  • Intubation: Avoid if possible; positive pressure ventilation can worsen RV dysfunction.
  • Fluids: Be judicious; even the smallest amount can worsen RV overload.
  • Vasopressors: Norepinephrine is preferred as first-line for hypotension/shock.
• Anticoagulation (Start Immediately):
  • Initial choice is UFH or LMWH (Lovenox).
  • Lovenox is preferred for quicker time to therapeutic range, but is contraindicated in renal dysfunction, older age, or need for emergent procedures.
  • DOACs can be considered for stable, low-risk patients as an outpatient.

Escalation for High-Risk PE

• Systemic Thrombolytics: Consider for very sick patients with shock/cardiac arrest (e.g., Alteplase 100 mg over two hours or a bolus in cardiac arrest). High risk of intracranial hemorrhage; weigh risks versus benefits.
• PERT Activation: Engage multidisciplinary teams (usually including ICU, CT surgery, and interventional radiology).
• Interventions: Consult specialists for catheter-directed thrombolysis or suction embolectomy. Surgical embolectomy can also be considered.
• Bridge to Care: Activate the ECMO team early for unstable patients to buy valuable time.

Prognosis & Disposition

• Mortality: Low risk < 1%; intermediate 3-15%; high risk 25-65%.
• Complications: 3-4% of patients develop Chronic Thromboembolic Pulmonary Hypertension (CTEPH). Others may have long-term RV dysfunction and chronic shortness of breath.
• Recurrence: ∼ 30% chance in the next few weeks to months, if not treated correctly.
• Disposition:
  • ICU: All high-risk and some intermediate-high risk patients.
  • Regular Floor: Intermediate-low risk patients.
  • Outpatient Discharge: Low-risk patients can be sent home on anticoagulation. Use PSI or HESTIA scores to risk stratify suitability, typically starting a DOAC.
• Shared Decision-Making: Critical to ensure care is safe and consistent with the patient’s wishes.