Differentiating disorders of ECF volume/Na content regulation versus disorders of total body fluid osmolarity/water regulation

Abstract

When one is teaching students who are new to concepts of body fluid and electrolyte regulation, a major challenge is to convey the separate but interactive nature of the two systems that respectively regulate extracellular fluid (ECF) volume/Na content and total body fluid osmolarity/water. We have developed a series of strategies/tools designed to both optimize conceptual understanding and translate concepts to clinical practice. These include 1) clear delineation of the distinct differences between the two homeostatic systems, reinforced in instructional objectives, lectures, and small group sessions; 2) anticipation and direct confrontation of the common 'Na content = Na concentration' error, soliciting student participation in ousting this misconception; 3) modification of terminology to clarify body fluid reality; 4) facilitation of active problem-based learning in small group sessions focused on clinical cases of increasing complexity (50% of course hours); 5) use of whole body/single-eyeful graphics to convey essential details within a clinically meaningful context; 6) standardization of diagnostic algorithms and pathophysiological graphs across lecturers and course components; and 7) provision of hands-on instruction/practice in physical examination of ECF volume in parallel with conceptual learning, thus emphasizing the importance of the bedside exam in detecting disorders of ECF volume/Na content. These approaches require an enthusiastic and well-prepared faculty committed to a high level of consistency and are designed for second-year students with a solid basic science background.