JJ 12 BNP for Diagnosis of Acute CHF

ED physicians are only about 80% accurate in their diagnosis of acute CHF. Why? There is no single element of past medical history, presenting symptoms or physical exam findings that can reliably rule in or rule out acute CHF in the ED. Orthopnea, PND and weight gain are not especially helpful in making the diagnosis and even the lauded S3 gallop which most of us cannot identify on the best of ED shifts is not that helpful. The classic signs of CHF are often absent on CXR and interobserver agreement (whether you are an ED doc or a radiologist) on the diagnosis of CHF by CXR is enormous. Nonetheless, when all of these elements are put together, ED physician clinical gestalt is not bad at diagnosing CHF. But we could do better. Enter BNP. BNP is currently in use in many EDs across North America and Europe. In this Journal Jam podcast we discuss the clinical utility of BNP and pro-NT-BNP in the work-up of the dyspneic ED patient. We ask the questions: does BNP add much beyond physician gestalt? Which patients might BNP be useful for? Should we abandon BNP as a dichotomous rule-in/rule-out variable and instead use it as a continuous variable? Does using BNP effect patient oriented outcomes? Is lung POCUS a better test? Are prediction models that include BNP useful? and many more.... Podcast production by Anton Helman, Justin Morgenstern & Rory Spiegel. Editing and sound design by Anton Helman, March 2018. Blog post by Anton Helman Cite this podcast as: Helman, A, Morgenstern, J, Spiegel, R. BNP for Diagnosis of Acute CHF. Emergency Medicine Cases. March, 2018. https://emergencymedicinecases.com/epinephrine-cardiac-arrest/. Accessed [date]. BNP is a vasoactive hormone that is released by strained myocardium from a variety of causes. Since its discovery about 30 years ago, BNP has been utilized as a biomarker for the diagnosis and prognosis of acute heart failure both in the ED and the inpatient setting. Many factors potentially alter BNP:  age, kidney disease, obesity, hypertension, coronary artery disease, atrial fibrillation, and chronic respiratory disease. Many of the patients in which we have diagnostic uncertainty about CHF are older, have renal disease, are obese, hypertensive with respiratory or other cardiac disease. Nonetheless, there have been several observational studies and RCTs examining the role of BNP in the ED as a diagnostic aid and there remains controversy as to its utility. This Journal Jam podcast reviews these studies and suggests a clinical bottom line.   EBM topic highlighted in this Journal Jam: Spectrum Bias Spectrum bias or case-mix bias is the inherent variability when performing a diagnostic test in different clinical scenarios. This is because in each clinical scenario you have a different case-mix or population of patients. As such, spectrum bias can be classified as a type of sampling bias. Tests unfortunately don’t perform the same along the spectrum of disease or across all populations. A tests accuracy depends on the prevalence and severity of the disease within the study population. If you have a discrepancy between the study population and the population you are looking at, the test will be inaccurate due to spectrum bias. Using a test in a cohort of patients that don’t have the disease in question – well that’ll inflate the sensitivity. If you test a population that obviously have the disease, then you’ll inflate the specificity. This has all to do of where patients lie on the disease spectrum. If you are looking at urine infections, a urinalysis will look a lot more sensitive if you only test young healthy males. On the other hand, it will look a lot more specific if you only test women coming in for a chief complaint of a typical UTI. In this case, it’s important to know what mix of patients the study is meant for. It’s important to contextualize the study population.