2013 First Sitting SAQs

23% pass. A good answer to this question required candidates to think broadly about how drugs act and have a system for classifying their actions. One possible classification is action via receptors or non-receptor actions. Many candidates used categories such as physiochemical, receptor and enzymes. Common problems were failure to mention a whole class of drug actions e.g. drugs acting via voltage-gated ion channels or gene transcription regulation. Candidates also gave far too much detail in some sections e.g. a description of zero order and first order kinetics is not required. Candidates often did not give examples of the drug action they described.

Most candidates performed well in this question. The physiology of cerebrospinal fluid (CSF) required candidates to write about CSF formation, circulation and absorption, compare the composition of CSF to plasma and describe normal volumes and pressures. The functions of CSF also need to be listed. Some candidates described the displacement of CSF when intracranial pressure rises as a function of CSF. No marks were given for this. The best approach to the anatomy of a lumbar puncture was to describe the lumbar intervertebral space at which the lumbar puncture is done and then describe the anatomical structures that the needle would traverse from the skin to the subarachnoid space. Mentioning the indications for a lumbar puncture was not required.

A good answer to this question required attention to detain and an ability to describe changes in many variables at each stage e.g. intrathoracic pressure, blood volumes, baroreceptor firing and the subsequent cardiovascular response (e.g. heart rate and blood pressure). Using graph(s) is a useful way to assist in the explanation and was requires as part of the answer. Dividing the response into four stages makes answering the question much easier. Overall there was a deficiency in a deep understanding of the integrated physiology associated with the Valsalva manouvre. The most common mistakes were describing a change but not saying why it happened, not considering each element at each stage and confusing terms e.g. saying increased cardiac output when the response was increased mean arterial pressure. Very few candidates drew accurate grahs. Graphs required were those of the changes in intrathoracic pressure, the pulse pressure response and the heart rate response

For a good answer candidates were expected to have an integrated knowledge of gastrointestinal physiology. Gut function is regulated by the enteric nervous system and by paracrine and endocrine hormones released by hormone secreting cells in the mucosa of the gut (enteroendocrine cells). These cells secrete hormones in response to neural innervation or in response to triggers associated with ingested food. Gut functions influenced include secretion, digestion, absorption and motility. The endocrine system also has an important role in the handling of nutrients following absorption and some mention of insulin was required.

A good answer would have best been served by a tabular structure and some understanding of the information required. One system of classification of oral hypoglycaemic drugs is by their mechanism of action, or drug group e.g. Biguanides, Sulfonylureas, Thiazolidinediones, Alpha-glucosidase inhibitors, Meglitinides and Dipeptidyl peptidase (DPP) -IV inhibitors. Click to Open CICMWrecks Pharmacopeia Table: Hypoglycaemic Agents

This question required anatomical detail relating to the upper airway and bronchial tree, which was generally answered well. The functional implications of a highly compliant chest wall in defending FRC and the relationship of FRC to closing volume was less clearly explained. Better answers mentioned the high physiological dead space, oxygen consumption and work of breathing. Additional points were awarded for discussing the immaturity of the respiratory control centre and propensity for apnoea. Common omissions included not providing comparative adult data or a written description of how neonates differed from adults (or the significance of this). Candidates confused chest wall compliance (increased in newborns) with lung compliance (reduced in newborns but rapidly approaches normal adult values as “specific compliance”). Increased oxygen consumption necessitates increased minute ventilation (with tidal volumes equivalent to adults on a weight basis) via respiratory rate. Functional Residual Capacity FRC (equivalent to adults) and Closing Capacity (increased relative to adults) were often confused. Better answers provided responses often in tabular format. Discussion of cardiovascular responses and response to drugs were not requested and gained no marks.

Outline type questions require a comprehensive list and a brief explanation of each major function of the kidney. This should have included water balance, electrolyte balance, endocrine function, filtration, metabolism, acid-base balance, excretion and blood pressure control. Adequate breadth was lacking in many answers. Marks were awarded for discussion of water reabsorption at specific points along the length of the nephron and the control mechanism through Aquaporins and ADH. It was expected answers would include calcium, magnesium, glucose and amino acid handling by the kidney (as well as sodium and potassium). Better answers discussed the elimination of fixed as well as volatile acids and outlined the role of ammonia. Discussion of the endocrine functions would include EPO, ,25 dihydroxy-cholecalciferol, prostaglandin E, renin, angiotensin II and kallekrein. Superficial responses such as, “the kidney is important in regulating volume” (or “waste” or “water” or “sodium”) were not sufficient.

This topic is a core aspect of respiratory physiology. The vast majority of the candidates could draw the oxygen cascade, but were let down by not having sufficient breadth and/or depth of information (e.g. alveolar gas equation was either omitted, inaccurate or poorly described in relation to the oxygen cascade) to describe the physiological principals at each step of the cascade.

Potassium is the second most common cation in the body and the main intracellular cation.
It is widely distributed and has many important roles. Maintenance of potassium balance
depends mainly on secretion by the kidneys in the distal and collecting tubules. Candidates
were expected to mention the influence of aldosterone, and other hormones such as
glucocorticoids, catecholamines and vasopressin have as well as factors such as
acidosis/alkalosis. Candidates who had a systematic and structured approach performed
better.

Most candidates answered the question under the subheadings absorption, distribution, metabolism and elimination. However, they didn’t give any details of the direction or mechanism of change, often used vague statements without specifically addressing the question and failed to give examples. The impact of the shock state on different kinetic parameters including absorption from skin, tissue, muscles, enteral absorption and inhalational was often overlooked. Similarly, the consequences of changes in volume of distribution, protein binding (e.g. albumin and globulin, ionisation) was poorly understood as was alteration in liver and kidney function. Although this topic is very broad candidates were asked to only outline the details of this topic.

Many candidates described the technique for insertion of an intercostal catheter which was not requested. Few identified the nerve supply to the area. Most identified the “safe” triangle but failed to correctly identify its borders or draw a diagram to show anatomic landmarks. Describing the anatomy from skin to lungs, including the neurovascular bundle, was needed to pass this part of the question. Although most knew that 100% oxygen reduce the nitrogen content in a pneumothorax and this accelerates its adsorption, but did not go on to provide any quantification of partial pressure changes in blood and in the pneumothorax bubble.

Overall, this question was well answered. Candidates were expected to classify the hypersensitivity reactions into their typical groups (Type I – IV) and to describe the mechanisms within each group. Similar such questions have been asked in previous exams. Again, those candidates who could provide some structure to their answer tended to score well.

This question asked candidates to compare and contrast the mechanism of action, pharmacokinetics, and side effects of these drugs in the context of the treatment of anaphylaxis. Information beyond that did not score marks. A structured approach (e.g. a table) assisted in presenting the information.

The liver has a unique dual supply – a portal venous system, and a hepatic arterial system, that floods the hepatic sinusoids and drain into the hepatic veins and then the inferior venacava. Knowledge of liver blood flow is essential for the understanding of certain pathophysiological mechanisms associated with disease and/or injury states of the liver. These two systems have unique characteristics, which most candidates seemed to have some knowledge of. A common area of weakness was the understanding/omission of the factors/mechanisms involved in the regulation of liver blood flow.

A fundamental aspect of cardiac physiology, that overall was well answered. The majority of candidates used figures to good effect. Candidates are reminded that all figures must be correctly labelled (e.g. X and Y axis, phases of action potential, etc.). Common omissions were those that reflected an adequate depth of knowledge (e.g. some of the current flows).

This is a core topic (syllabus Level 1) and a high level of understanding was expected. Overall candidates failed to demonstrate sufficient depth and breadth in their knowledge. A structured response considering the three basic elements underpinning the control of alveolar ventilation (the Sensors, Central integration and control and the Effectors) was core material. A detailed description of each was expected.

Overall answers lacked structure and depth, to what is a very fundamental topic. This topic is generally covered within the opening chapters of most physiology texts. Common errors were not answering the question, writing lists rather than describing and explaining, and poor categorisation. Candidates were expected to mention and give example for mechanisms such as hormones binding to cytoplasmic or intra-nuclear receptors, binding to transmembrane receptors coupled to G proteins, cAMP, cGMP, tyrosine kinase, etc.

Candidates often appeared to have a sufficient awareness of the choice of drugs (e.g. oxytocin analogues, ergot alkaloids, beta-receptor agonists, calcium channel blockers, etc.), but then failed to produce sufficient depth of knowledge to adequately describe their mechanisms of action in respect to uterine tone. Candidates are reminded that if asked to mention side effects, mentioning side effects of greatest relevance to intensive care (e.g. bronchospasm) in addition to the more generic side effects (e.g. rash). Click here for CICMWrecks Pharmacopeia Table for Oxytocics and Tocolytics