G1.ii · Acid–Base Disturbances

This VIVA will examine acid-base and renal physiology and pharmacology. Outline the principles of the Stewart (physicochemical) approach to acid base disturbances. Using this approach interpret the arterial blood gas below. (Image removed from report.)

a period of prolonged vomiting. An arterial blood gas analysis was performed on room air, revealing the following findings. pH 7.59 (7.35 – 7.45) PaCO2 58 mmHg (35 – 45) PaO2 72 mmHg (90 – 110) HCO3- 59 mmol/L (22 – 32) Interpret the findings. This viva tested the candidate’s knowledge of renal physiology related to the control of urinary pH, effects of acetazolamide and frusemide upon metabolic acid base state and respiratory response to metabolic acid base changes. The main points expected for a pass were knowledge of : • Respiratory response to changes in metabolic acid base. Use of correctly labelled graph or common formulae • Renal handling of H+ at the proximal and distal tubules. • Mechanism of HCO3- reabsorption and regeneration • Urinary buffers such as phosphate, ammonia and glutamine • Mechanism of frusemide associated metabolic alkalosis • Affect of acetazolamide on HCO3- The use of illustrations greatly assisted candidates to answer questions within this viva Syllabus : D1-2e, D2a and B1c-2a & b Reference : Textbook of Medical Physiology by A. C Guyton & J. E Hall.