Exploring the Relationship Among BNP, Fluid Status and Acute Kidney Injury in Critically Ill Patients

B-type natriuretic peptide (BNP) is rapidly released by the ventricles of the heart in response to myocardial stretch. This cardiac neurohormone is mostly elevated in patients with fluid overload or myocardium dysfunction. BNP is a very useful and important marker. It can predict mortality and cardiac events in patients in the ICU setting. In stable hemodialysis patients with normal LV function on echocardiography, high BNP levels are likely the result of blood volume expansion and require reduction in postdialysis dry weight. On the other hand, ample recent data have highlighted the role of fluid accumulation on mortality and non-recovery of kidney function in critically ill patients with acute kidney injury (AKI). In the past, there were many methods to evaluate fluid status. Some are not reliable such as central venous pressure or physical examination. Some are invasive and expensive such as Swan Ganz、PiCCO catheter or bioimpedance device. Nevertheless, About the relationship between BNP and fluid status, a study found a significant relation between bioimpedance-derived body composition (BC) (fluid distribution) parameters and BNP concentrations. This relationship was independent of the cardiac history of the patient and suggests that the natriuretic peptide levels are to some degree modifiable by changing a patient's fluid distribution. In this study, we want to observe that if the level of BNP can predict the occurrence of acute kidney injury and the need of renal replacement therapy. Besides, we also want to see if BNP can be a useful and convenient marker to guide adjustment of optimal fluid status and then to improve outcome.