Pulmonary embolism

Quick Overview

Pulmonary embolism (PE) is a life-threatening condition requiring rapid diagnosis and treatment. NICE NG158 provides a structured approach using clinical probability assessment (Wells score), D-dimer testing, and imaging to confirm diagnosis, with immediate anticoagulation for most suspected cases. Risk stratification guides safe outpatient management versus admission.

Core Facts & Concepts

Two-Level PE Wells Score

• PE likely (>4 points): Proceed directly to CTPA
• PE unlikely (≤4 points): D-dimer first; if positive → CTPA

D-dimer Limitations

• High sensitivity (>95%), low specificity (~50%)
• False positives: pregnancy, malignancy, infection, post-op, elderly, hospitalised patients
• Age-adjusted threshold: age × 10 μg/L (for age >50 years)
• 🚩 Never use in "PE likely" patients - delays diagnosis

Imaging Selection (NICE NG158)

• First-line: CTPA - sensitivity 83%, specificity 96%
• V/Q scan if: contrast allergy, renal impairment (eGFR <30), pregnancy with normal CXR
• V/Q reported as: normal, low/intermediate/high probability

Immediate Anticoagulation

• Start before imaging if Wells >4 AND delay >1 hour expected
• Options: DOAC (apixaban/rivaroxaban), LMWH, or fondaparinux
• 📊 Contraindications: active bleeding, platelets <50×10⁹/L, recent neurosurgery

Problem-Solving Approach

Step-by-Step Diagnostic Pathway

1. Calculate two-level Wells score immediately
2. Wells ≤4 (PE unlikely):
   • Measure D-dimer (age-adjusted if >50 years)
   • Negative D-dimer → PE excluded, no imaging
   • Positive D-dimer → CTPA (or V/Q if contraindicated)
3. Wells >4 (PE likely):
   • Start anticoagulation if imaging delay >1 hour
   • Arrange immediate CTPA (or V/Q)
4. PE confirmed → Risk stratify using sPESI

🚩 Red Flags for Massive PE

• Systolic BP <90 mmHg or drop >40 mmHg
• Syncope, altered consciousness
• Severe hypoxia (SpO₂ <90%)
• Cardiac arrest
• → Consider thrombolysis (alteplase 50 mg IV over 1-2 hours)

Analysis Framework

Risk Stratification: Simplified PESI (sPESI)

• sPESI = 0: Low risk → outpatient management safe (mortality <1%)
• sPESI ≥1: Higher risk → consider admission, troponin/BNP, echo

Outpatient Management Criteria (All Must Apply)

• sPESI = 0
• No active bleeding/high bleeding risk
• Adequate social support
• Normal renal/hepatic function (for DOACs)
• Follow-up within 24 hours arranged

Visual Aid

CTPA vs V/Q Selection

Key Points Summary

✓ Two-level Wells >4 = PE likely → skip D-dimer, go straight to CTPA; start anticoagulation if imaging delayed >1 hour

✓ Age-adjusted D-dimer (age × 10 μg/L for >50 years) reduces false positives in elderly; never use in "PE likely" patients

✓ CTPA is first-line imaging; V/Q scan reserved for renal impairment, contrast allergy, or pregnancy with normal CXR

✓ sPESI = 0 permits safe outpatient management (mortality <1%); sPESI ≥1 requires admission and further risk assessment

✓ DOACs (apixaban/rivaroxaban) are first-line anticoagulation; no bridging with LMWH needed unlike warfarin

✓ Massive PE (hypotension/arrest) → consider thrombolysis with alteplase 50 mg IV; contraindications include recent surgery/stroke

✓ Common pitfall: Delaying anticoagulation in high-probability PE waiting for imaging - start treatment first if Wells >4 and delay expected