Investigations Summary

1. Investigations Summary • Use Well’s Criteria to determine pre-test probability • D-Dimers, a degradation product of cross-linked fibrin, can be used in low probability cases of suspected PE or DVT to rules out the diagnosis • Clinically suspected PE - Patient haemodynamically unstable (ie. In shock), urgent CTPA required, if not available urgent ECG • If patient haemodynamically stable • Everybody gets a chest xray… • Low probability- CXR and D- Dimers • Higher probability- CTPA gold-standard, if contraindicated or unavailable V/Q scan • If initial imaging negative but still high clinical suspicions, do the other scan CTPA/VQ +/- US of lower limbs • Clinically suspect DVT - Ultrasound + doppler • Imaging has a high specificity, but not necessarily high sensitivity…. Clinical reasoning is very important

2. Assessing the Risk / Benefit Ratio of Imaging Essentially the rules are: • The potential benefit of the test should always outweigh the risk. • A diagnostic imaging examination is indicated only if it is likely to be useful in the management of the patient and if the risk of the procedure is less than the risk of missing a treatable disorder. • It is the responsibility of the imaging specialist to ensure radiation dosage during imaging is kept to a minimum according to the ALARA principle (As Low As Reasonably Achievable), while maintaining the diagnostic quality of the examination. Before requesting an imaging investigation, the referring doctor must ask him/herself the following questions: 1. Have I taken a history, performed a physical examination and come to a provisional clinical diagnosis? (the significance of the result of a test cannot be assessed without a pre-test probability of the disease being tested for) 2. Is imaging indicated? • Am I duplicating recent tests? • Will it change my diagnosis? • Will it effect my management? • Will it do more harm than good? 3. If imaging is indicated, is a test that does not employ IR a feasible option (Ultrasound or MRI)?