To PERC, or not to PERC?
Mahir Mameledzjuia MD, MBA
Editor: Omar Lopez, MS3
1) What clinical prediction rule can be used to identify a group of patient at very low risk for PE (pulmonary embolism) for whom no additional diagnostic workup is required?
Why do we care?
PEs are scary and dangerous
Brief Tidbit on Pathophysiology:
Risk factors put you at higher risk, and like a teeter-totter, patients present on a spectrum. Taking a thorough history and combining that with your clinical gestalt can parse out how you work up patients with a PE. In adult patients with suspected acute pulmonary embolism (PE), can a clinical prediction rule be used to identify a group of patients at very low risk (<15% risk of PE) for the diagnosis of PE for whom no additional diagnostic workup is required? ACEP’s policy is clear and follows with Level B Recommendations: For patients who are at low risk for acute PE, use the Pulmonary Embolism Rule-out Criteria (PERC) to exclude the diagnosis
What is the PERC rule?
Remember, using the PERC rule is only appropriate in patients who is at very low risk (<15% risk of PE) for the diagnosis of PE. This can be done through clinical gestalt, or through using the two or three-tiered Wells score. There have been studies which have compared clinical gestalt to these decision rules, and clinical gestalt assessment seems to perform better than clinical decision rules (Wells, rGeneva) at estimating the pretest probably of PE and classifying patients with low and high clinical probability [Penaloza A, Verschuren F, Meyer G, et al. Comparison of the unstructured clinician gestalt, the Wells score, and the revised Geneva score to estimate pretest probability for suspected pulmonary embolism. Ann Emerg Med. 2013;62(2):117-124.e2].
Before its application you have to appreciate the importance of clinical judgement and history taking prior to its use. Risk stratify, and apply the rule appropriately based on stratification. The PERC rule requires a clinical suspicion of <15% before it can be applied; it should not be applied to all patients in whom you are considering PE. Similarly, the Wells score is not meant to be used on all patients with chest pain or dyspnea; you must first have a genuine clinical suspicion for PE. And finally, these tools do not force you to order any diagnostic testing. A positive PERC is not an indication for ordering a d-dimer, and a high-risk Wells score does not necessarily mean you must order a CTPE. Think through each individual patient, be mindful of how you are working up these patients. These tools can be helpful in finding the appropriate balance between being too conservative and too cavalier about PE.
Some food for thought: