F1.iii · Plasma Osmolality

This VIVA will examine renal physiology and pharmacology. How does the kidney concentrate urine? (Image removed from report.)

This VIVA will examine fluid physiology. How is water distributed in the body and how are these compartments measured?

This viva will explore your understanding of urea and renal tubular function. Why do we produce urea and how effective is it as an osmole?

This viva is on the physiology and pharmacology as it relates to blood volume and tonicity. Outline the response to loss of 1 L of circulating blood in an adult.

This viva tested knowledge of intravenous fluid physiology and pharmacology and concepts of osmolarity, osmolality and tonicity.

This Viva will explore your knowledge of fluids and colligative properties. What is in a bag of 0.9% Saline? Subsequent questions explored knowledge of osmolality, osmolarity, mannitol, colligative properties of fluids, anion gap, classification of diuretics and mechanism of actions.

This Viva will examine knowledge of intravenous fluids, colligative properties What is in a bag of Normal Saline? Areas of knowledge that candidates were tested on included concepts of osmolality, osmolarity, anion gap, mannitol, and colligative properties of fluid. In addition this viva tested knowledge of the pituatary gland, specifically anatomy, hormones secreted and in particular, Anti Diuretic Hormone.

The initial information given to the candidates was – This is an analysis of urine from a patient on the intensive care unit: Glucose negative Ketones trace pH 6.0 urobilinogen moderate Specific gravity >1.030 You will be asked to comment upon these findings In this viva candidates were asked to explain the physiological basis to the urinanlysis provided above. Further knowledge was sought in reference to ketones and ketone body generation and metabolism, generation of urobilinogen and significance of specific gravity.

In order to pass this viva, candidates were expected to know the distribution of water in different body compartments, the difference in electrolytes composition in different compartments (E1), definition of osmosis and diffusion, and where osmosis and diffusion occurs in the body (B1f and D1), measurement and calculation of osmolality (E1), and how different intravenous fluids will be distributed in different body compartments (E2a). The common deficiency in the candidates’ answers included the difference in electrolytes composition between interstitial fluid and plasma and the reason behind it (F2a), how osmolality can be measured, the presence of an osmotic process in the medulla of the kidney where re-absorption of water occurs through the collecting tubules in the presence of anti- diuretic hormone (D1), and how the fluids will be distributed in the body when different intravenous fluids are administered. Syllabus : E1 2 References : Chapter 1 of Review of Medical Physiology by Ganong Vander’s Renal Physiology for details on this topic.