Pulmonary embolism (PE)

Venous thrombi, usually from DVT, pass into the pulmonary circulation and block blood fl ow to lungs. The source is often occult.

Investigations

2-level Wells’ score for PE risk stratify.
Urea & Creatinine
Electrolytes
CBC
Baseline clotting
ECG: commonly normal or sinus tachycardia; right ventricular strain pattern V1–V3 right axis deviation, RBBB, AF, may be deep S waves in I, Q waves in III, inverted T waves in III (‘SI QIII TIII’).
CXR: often normal; decreased vascular markings, small pleural effusion Wedgeshaped area of infarction. Atelectasis.
ABG: hyperventilation + poor gas exchange: PaO2, PaCO2, pH.
Serum D-dimer:
- low specificity (increases if thrombosis, inflammation, post-op, infection, malignancy), so check only in patients with low pre-test probability.
- A -ve D-dimer in a low-probability patient effective excludes PE
CT pulmonary angiography (CTPA)
- Sensitive and specific
- The test of choice for high-risk patients or low-risk patients with a +ve D-dimer. - If unavailable, a ventilation–perfusion (V/Q) scan can aid diagnosis but frequently produces equivocal results

If good story and signs, make the diagnosis. Start treatment before definitive investigations: most PE deaths occur within 1h.
Oxygen if hypoxic, 10–15L/min
Morphine 5–10mg IV with anti-emetic if the patient is in pain or very distressed
IV access and start LMWH/fondaparinux
If low BP give 500mL IV fluid bolus Get ICU input
Haemodynamic instability
- Unstable: Consider thrombolysis (eg alteplase 10mg IV bolus then IVI 90mg/2h)
- Stable: If persistent low BP consider vasopressors, eg dobutamine 2.5–10mcg/kg min IV or noradrenaline; aim for systolic BP >90mmHg
Long-term anticoagulation
- DOAC: switch directly from LMWH
- Warfarin: continue LMWH until INR >2
- If obvious cause, 3 months of anticoagulation may be enough; otherwise, continue for ≥3–6 months (long term if recurrent emboli, or underlying malignancy).
- Investigate underlying cause, eg thrombophilia, SLE, or polycythaemia
- Consider malignancy: check CXR, CBC, LFT, Ca2+; urine alysis; consider CT abdomen/pelvis and mammogram.