SAQ 436 – Respiratory – suspected pulmonary embolism imaging and thrombolysis
Model Answer
Respiratory – suspected pulmonary embolism imaging and thrombolysis.
a. D-dimer
- No useful role: pre-test probability is high, so definitive imaging or bedside evidence of massive PE is required rather than rule-out testing.
b. Imaging options
| Investigation | Pros | Cons |
|---|---|---|
| CT pulmonary angiogram | Widely available, quick, and can identify alternative thoracic pathology. | Requires contrast with allergy/nephropathy risk; radiation; unstable patient may deteriorate away from ED. |
| Echocardiography/TOE | Bedside, no radiation, and can show right-heart strain in massive PE. | Operator dependent; indirect test and less useful for segmental emboli. |
| V/Q scan | Lower radiation and may be useful if contrast is contraindicated or prior V/Q is available. | Often delayed, may be indeterminate in elderly lungs, and does not diagnose alternative pathology. |
| Lower limb Doppler ultrasound | Bedside, no radiation, and may provide indirect evidence when unstable. | Requires skilled operator and does not directly diagnose pulmonary embolism. |
c. Thrombolysis indications
- Cardiac arrest where PE is the likely cause, with expectation of prolonged resuscitation.
- Massive PE with persistent hypotension, for example systolic BP below 90 mmHg for more than 15 minutes.
- Evidence of right-heart strain with clinical compromise or positive biomarkers in selected intermediate-high-risk PE.
- Large clot burden such as main pulmonary trunk involvement may be considered in selected patients.
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