2011 First Sitting SAQs

The question related to physiological changes occurring when FiO2=1. Many candidates focused on the toxic effects of oxygen, which were often incorrect (CNS symptoms will not occur at one atmosphere). Candidates simply lacked knowledge, those that did have some understanding failed to provide adequate detail (ie. it was occasionally mentioned oxygen stores are increased but not the mechanism by which or extent to which stores are increased). In addition, it was expected that candidates would outline and describe the mechanism behind the changes in PaO2in arterial and mixed venous blood, shift in CO2 ventilation, hypoxic pulmonary vasoconstriction as well as pulmonary toxic effects.

this question. Most candidates had a basic knowledge of diaphragmatic function however were uncertain of anatomy and rarely related the two. Candidates were expected to describe the attachments of the diaphragm, openings, nerve supply, actions, including it’s role upon the oesophageal sphincter Syllabus: B1b 2c Recommended sources: Anatomy for Anaesthetists, Ellis and Feldman, pages 317 - 323

this question The question sought an understanding of the diverse roles of calcium. Some candidates spent considerable time in details of one or two roles. Limited marks were awarded for demonstrating knowledge of calcium distribution & homeostasis. Few candidates had a good understanding of the differences between calcium chloride and gluconate.

this question. A number of candidates had absolutely no understanding of this subject. Some candidates had a basic understanding of either digestion or absorption but few demonstrated knowledge of both processes. Inaccuracies were common with many discussing the role of the gastric acid & enzymes in carbohydrate digestion. Most forgot to mention simple dietary carbohydrates. For a good answer candidates were expected to outline the forms of dietary carbohydrates, gastro-intestinal enzyme action and mechanism of absorption Syllabus: Q1, 2c Recommended sources: Review of Medical Physiology, Ganong, Chp 27

this question. Candidates were expected to provide a definition of important terms such as mixed venous. Many candidates provided much information about the partial pressure of carbon dioxide in arterial blood without discussing the factors which alter the mixed venous pressure. Partial pressure of CO2 in mixed venous blood depends on the CO2 content of the mixed venous blood, which in turn represents a balance between CO2 production in the tissues and the CO2 content in arterial blood. Good answers demonstrated an understanding of this and provided relevant details about these aspects. The partial pressure of CO2 is related to the CO2 content by the CO2 dissociation curve, the position of which is determined by the state of oxygenation of haemoglobin, the Haldane effect. CO2 production is related to aerobic metabolism in cells and total production is defined by the metabolic rate. Examples of increased and decreased CO2 production gained additional marks. The partial pressure of CO2 in mixed venous blood is related to the partial pressure or content of CO2 in arterial blood. This is determined mainly by alveolar ventilation under the control of chemoreceptorsand the brainstem respiratory centre. Syllabus: B1h, 2c Recommended sources: Applied Respiratory Physiology, Nunn 5th edition, Chp 10 pages 222 to 239

this question. An approach that covered the main determinants of right ventricular cardiac output including heart rate, right ventricular preload, contractility, afterload and the relationship with left ventricular output, ventricular interdependence, and the respiratory system would have provided the framework for a good answer. Some candidates used this approach but described more features of left ventricular than right ventricular output. The observation that the right ventricle is relatively thin walled and its output is very sensitive to changes in right ventricular preload and afterload particularly was central to this question. The unique shape of the right ventricle and its contraction characteristics involving ventricular interdependence were rarely mentioned. Also details on right ventricular afterload and the importance of factors affecting pulmonary vascular resistance were lacking in most answers. Syllabus: C1c Recommended sources: Review of Medical Physiology, Ganong, Chps 31 and 33, Textbook of Medical Physiology, Guyton & Hall Chp 9 and 20

this question. A useful introduction could include a definition of medullary concentration gradient and its function. The answer was expected to describe the roles of sodium, chloride and urea in the countercurrent multiplier and the features of the vasa recta countercurrent exchange system. The 3 main areas that needed to be addressed to pass this question included: [1] The loops of Henle with their water permeable descending limbs and water impermeable ascending limbs, which actively remove solutes from the tubular lumen. The counter current multiplier system. [2] The vasa recta which run parallel to the loops of Henle and are permeable to water and solute and have low flow. This allows the medullary concentration gradient to be maintained. The counter current exchange mechanism. [3] The role of urea which is concentrated in the medulla by mechanisms which involve changes in permeability to urea in different regions of the tubules partly influenced by the effects of antidiuretic hormone. Some candidates elected to draw the loop of Henle and vasa recta together with the movement of various solutes and water and answer the question from it. Unfortunately mistakes in these diagrams only confused their answers further. Syllabus: Section D1, 2c Recommended sources: Principles of Physiology for the Anaesthetist, Power and Kam, page 234

The first part of the question on bactericidal activity of gentamicin was better answered than the second part on its toxicity. Details on the cellular mechanisms of bactericidal action and toxicity were lacking in most answers. Most candidates did not appreciate that gentamicin is avidly accumulated and retained by proximal renal tubular cells in concentrations many times higher than the plasma concentration. Also these high tubular cell concentrations of gentamicin are maintained long after the plasma concentrations have fallen to very low levels, thus enhancing its toxic effects. Gentamicin has multiple toxic effects within the tubular cell including adverse effects on protein synthesis, translation and folding, impairment of mitochondrial function and production of reactive oxygen species and damage to the nucleus. Syllabus: M2a, 2d. Recommended sources: Pharmacological Basis of Therapeutics, Goodman and Gillman, Chp 45 and page 1162

this question. Answers framed around the structure of absorption, distribution, metabolism and excretion performed better. An approach based on the physiologic changes of pregnancy performed less well because important areas of pharmacokinetics were omitted. The effects of pregnancy on oral absorption should have included a discussion of gastrointestinal motility, nausea and vomiting and gut blood flow. Absorption from sites other than the gastrointestinal tract, such as skin, lung and the epidural space and the effect of pregnancy on these should have been mentioned. Many answers were vague on the effects of increases in total body water and plasma volume and cardiac output and changes in plasma protein binding on the distribution of drugs. Most answers did not provide enough specific examples. The effect of pregnancy hormones on liver enzyme activity were mentioned by few. Syllabus: Generic Pharmacology III 2d Recommended sources: Foundations of Anaesthesia: Basic clinical Science. Hemmings and Hopkins, and Anaesthesia, Miller.

this question. Most candidates chose to describe the thermodilution technique of cardiac output measurement. Descriptions of other techniques and indicators such as dye dilution using indocyanine green were acceptable alternatives. Better answers included a description of the Fick Principle and the fact that it is based on the law of conservation of matter. For thermodilution, heat lost from the blood = heat gained from the injectate. Also required were an accurate description of the technique, a description of the indicator-time curve and errors encountered in the technique. For thermodilution these included the requirement for a Swan Ganz catheter, nature and temperature of the injectate, temperature measurement using a thermistor in the pulmonary artery and an appreciation that it is the curve of a decrease in temperature versus time that is being analysed. Syllabus: S2c Recommended sources: Anaesthesia, Miller, Chp 40

this question. Candidates were expected to provide sufficient detail in answers. Extra marks were awarded for diagrams relating the ECG accurately to pressure events during the cardiac cycle. Time intervals, units of measurement and clear labels were essential for diagrams. Mechanisms pertaining to ion flux and ion channels needed to be specifically explained. Discussion of mechanisms needed to be accurate and relevant to the effect on the ECG. For example, better answers noted that AV conduction was depressed by Digoxin, predominantly due to an increase in Vagal tone

this question. The question was answered well overall. Better answers included detail of the platelet receptor and mediator interactions. Discussion of the role of the platelet in providing a phospholipid surface to enable the formation of the activated Xa complex was expected. Modulation of the coagulation cascade and prevention of clot propagation via protein C, nitric oxide, thrombomodulin and fibrinolysis was important to note in a comprehensive answer. The pharmacodynamic action of aspirin was generally understood. Syllabus: J1,2c and J2, 2d Recommended sources: Basic and Clinical Pharmacology, Katzung, Chp 34, 36

this question. The question required an accurate statement of Starling’s Equation, including the filtration and reflection co-efficients, and definitions of terms. Marks were awarded for numerical values pertaining to hydrostatic and oncotic pressure gradients and net filtration in a 24 hour period. A satisfactory answer explained the factors which cause imbalance in Starling’s relationship including; precapillary vasodilation, increased venous pressures, gravity/ posture, fall in plasma protein concentration, changes to capillary permeability and lymphatic obstruction. Syllabus: E1 Recommended sources: Review of Medical Physiology, Ganong, Chp 23 and other sections

this question. To pass this question, the candidate only needed to define a buffer (weakly ionised acid or base in equilibrium with its full ionised salt), what it does, then discuss how Haemoglobin functions in this capacity. In that regard, brief review of how CO2 is buffered, the role of haemoglobin histidine residues, buffering capacity of oxy haemoglobin and deoxy haemoglobin and how this contributes to the Haldane effect would have rounded out a very good answer. Additional credit was given for an understanding that histidine contains an imidazole group and how these groups are effective as a buffer. Few candidates mentioned that haemoglobin was quantitatively significant and no candidate mentioned that it is the primary buffer for CO2. Many answers were quite brief and did not explore the subject matter asked. Syllabus: B1h, 2c, 2b and Section F Recommended sources: Nunn’s Applied Respiratory Physiology, Lumb, page 228 to 230

this question. Providing a statement about what vaccines do followed by some detail about the processes involved in triggering a response and the nature of that response in both Innate immunity and acquired immunity would have achieved a good pass. Many candidates failed to adequately describe the nature of the primary and the secondary response to antigen exposure. The fact that previous immunisation enabled a brisk secondary response was recognised by most candidates but that this was largely due to the proliferation of IgG antibody producing B lymphocytes and effector T cells was not appreciated. Many answers simply did not include sufficient information to achieve a pass mark. Syllabus: M2i Recommended sources: Review of Medical Physiology, Ganong, Chp 3

this question. One possible way to answer this question is to offer a definition of the diastolic period then to split the events up for description into mechanical events, ECG events and electrical/ionic events. Few candidates defined the diastolic period, and whilst many talked about opening and closing of valves, there was generally a poor understanding of the sequence of events whereby the left ventricle comes to be filled with blood. The better answers included a description of the ionic events that occurred at the various stages of diastole. Many answers lacked any reference to the ECG events in diastole. The major weakness in answers was again the failure to include sufficient information to achieve a pass mark. This was probably as a result of the lack of a systematic approach when answering a question of this nature. Syllabus: C1b, 2d,e and C1c, 2e,f Recommended sources: Textbook of Medical Physiology, Guyton & Hall, Chp 9 – 11 and Review of Medical Physiology, Ganong, Chp 31

this question. Moderately well answered overall, however many candidates lacked a systematic approach to their comparison of the pharmacology of drugs that alter the pH of gastric fluid. Few candidates discussed pharmacokinetics in sufficient detail, with only a very limited discussion comparing the absorption, metabolism and elimination of even common drugs. Relevant information such as bioavailability, duration of effect, and available formulations with dosing was often lacking. Similarly, little attention was given to important drug interactions. Many candidates included drugs which are used for gastric problems or mucosal protection, but do not specifically influence gastric pH e.g. sucrulfate. Some candidates gave unnecessarily detailed accounts of the physiology of gastric fluid production and the acid-base mechanisms involved. All candidates provided details of H2 blockers and PPIs, but often did not list representative examples or compare the effects on basal versus stimulated acid secretion. Many candidates also discussed antacids, but did not indicate their mechanisms of action properly and did not outline potential adverse effects. Some candidates included prostaglandin analogues and anticholinergic drugs for completeness and were able to indicate their roles in affecting gastric acid secretion. Syllabus: Q2a 2b,c Recommended sources: Basic and Clinical Pharmacology, Katzung, Chp 62

this question. This question required candidates to describe the physical principles of blood flow through a dialysis circuit and the movement of solute across a dialysis membrane. While most candidates were able to allude to important factors contributing to the flow of a fluid through a hollow tube, few did so in a systematic way and only some provided relevant formulae showing the relationship between pressure, fluid viscosity and tube resistance. A short discussion proceeding to flesh out the factors that determine blood viscosity, circuit pressures and practical examples was expected. Some candidates discussed convective processes extensively, which was not required in this question focussed on dialysis. Most candidates were able to describe the physical chemistry involved in diffusion across a semipermeable membrane in basic terms, however few provided sufficient details of these important principles. Very few candidates went on to properly discuss electrochemical forces affecting solute and water movement across a membrane or the factors that influence the performance of dialytic therapies in practical application. Syllabus: A2c, R2e, D1, 2b,c Recommended sources: Basic Physics and Measurement in anaesthesia, Davis and Kenny, various sections. Also Review of Medical Physiology, Ganong, chp 2, 32