Disorders of Volume: Core Curriculum 2025.

Historically, the paradigm for all maladies was associated with an imbalance of the 4 humors: blood, black bile, yellow bile, and phlegm. Although our understanding of disease has evolved significantly since the time of Hippocrates, a similar cornerstone of inpatient and ambulatory care involves understanding and correcting imbalances of volume. The kidneys are the principal organs controlling extracellular volume, capable of both sensing and altering salt retention through multiple redundant pathways, including the sympathetic nervous system and the renin-angiotensin-aldosterone system. Various disease states including sepsis, heart failure, and liver cirrhosis can dramatically alter the movement of volume across body compartments, leading to pathologic responses. Greater understanding of the role of the endothelial glycocalyx, the harms of volume overload among critically ill patients, and the impact of venous congestion on kidney function has challenged the traditional paradigms of volume management. Because both hypovolemia and hypervolemia are symptomatic conditions associated with adverse outcomes, managing volume is an essential skill for the nephrologist. In this Core Curriculum, we review the physiology of volume disorders and management strategies through a series of clinical cases.