Number Needed to Scan: Evidence-Based Point-of-Care Ultrasound (POCUS).

Interest and enthusiasm, regarding the use of point-of-care ultrasound (POCUS), continues to grow among clinicians in multiple medical specialties. Ultrasound machines technology has advanced to allow for smaller, even handheld machines. Integration of automated imaging technology has made these machines more user-friendly. However, one of the concerns with the widespread availability of POCUS is the overuse and misuse of this technology. In order to maximize the clinical impact of POCUS, this manuscript seeks to discuss a novel concept called the "Number needed to scan" (NNS). The NNS is an expression of the number of POCUS examinations needed to be performed to attain a benefit to the patient or to prevent an adverse outcome of a procedure. NNS serves a dual purpose: it can help clinicians understand the magnitude of clinical impact when they apply POCUS, and it can help clinicians explain this magnitude in layman terms to their patients. In this manuscript, we have focused our NNS calculations on landmark articles in three major categories: change in management; safety and accuracy; and catching a missed diagnosis. As clinicians seek to be good stewards of POCUS, NNS should be a concept used to consider which patients will be most likely to benefit from a clinician performed ultrasound.