Pulmonary embolism guidelines: will they work?

wo years ago several members of the British Thoracic Society independently suggested that, in the light of recent publications, the Standards of Care Committee should update their 1997 advice on suspected acute pulmonary embolism (PE). This issue of Thorax contains the results of this endeavour, with evidence sufficiently robust now to allow these to be called guidelines (see pp 470–83). Those familiar with the previous publication, to which the new document frequently refers, will recog-nise that the same basic structure has been used. Previously, the main recommended option in the face of a non-diagnostic ventilation-perfusion (V/Q) scan was pulmonary angiography, an invasive test that was little used before and probably little more after. This advice has been made redundant by developments in CT pulmonary angiography (CTPA), with strong evidence that, even though a negative result may not entirely exclude PE, it does make anticoagulation unnecessary. There is no doubt that CTPA should now be considered the central imaging investigation in suspected PE, and many acute hospitals are developing experience of the techniques. However, this adds a considerable workload to radiology departments already struggling to cope with the increased imaging requirements for cancer staging, not helped by the fact that PE is confirmed in only 20–35% of those where it has been suspected. This has led to different strategies for reducing the number of unnecessary CTPAs, but these too have their problems. Some hospitals continue to use V/Q scanning as a way of obtaining a definite answer, but 30–50% of such patients will require CTPA anyway, which delays definitive investigations and lengthens hospital stay, and others do not have nuclear medicine on site. Indeed, were CTPA easily and rapidly available, V/Q scanning would become largely obsolete. " There is no doubt that CTPA should now be considered the central imaging investigation in suspected PE " Another approach is to restrict CTPA to patients who do not have the combination of low clinical probability and a negative D-dimer test. Since this halves the number requiring lung imaging it is an attractive option, but practical experience shows that there are pitfalls. Firstly, although the 1997 clinical probability assessment system has been retained (now on good evidence), the fact that it is very simple does not mean that junior doctors use it properly, as many senior clinicians and radiologists have discovered. Secondly, the seductive simplicity and low cost of D-dimer assays mean that, in …