1. SAQ 7 Don Liew June 2015

2. Read the Stem A 20 year-old woman with a history of diabetes mellitus presents to your ED with fever, acute respiratory distress and chest pain. Vitals signs on arrival (pre treatment): GCS14 (E4,V4,M6) HR128 bpm BP85/45mmHg SpO 2 90% on 10L/min O 2 via Hudson Mask

3. Thoughts on the Stem Sick young woman with profound hypoxia and impending cardiovascular collapse. Respiratory sepsis and massive pulmonary embolism are 2 key Dx that come to mind. The arterial blood gases are expected to show features consistent with these, viz very high A-a gradient and HAGMA.

4. Qi The Aveolar Gas Equation No apologies for revising a basic physiological concept. This Q tests your knowledge about alveolar pO 2 (PAO 2 ), and how it’s determined by key variables: – PiO 2, which itself is affected by FiO 2 – pACO 2, which is practically same as paCO 2 – The Respiratory Quotient

5. Qii Alveolar – arterial Gradient Another basic concept. Most candidates know and use the combined formula, but were unable to demonstrate how the key parts work. Difference between oxygen in alveoli and systemic arteries is a key measure of effectiveness of: oxygen diffusion capacity and / or pulmonary circulation (if abN, this is known as shunt) Pneumonia is one example of the first, PE is one example of the latter. Both are very possible in our patient.

6. Qiii Causes of High A-a Gradient You were asked to identify causes of her profoundly high A-a gradient. Interpreting the stem, this should have been easy to answer. As mentioned, pneumonia and PE were the key differentials. Not only because of likelihood, but also because of potential to kill her unless treated. As such, these were both pass criteria. Had to mention both to score 2/2. Otherwise, scored zero for this section.

7. Qiv Anion Gap Another basic concept. Answers with or without K were acceptable. Tip: Always show your basic formula. In case your maths is wrong, we can at least allocate you half or more marks.

8. Qv Causes of HAGMA Easy Q in which most candidates scored 2/2. Lactic acidosis and ketoacidosis obviously the most important causes. Answers that did NOT score points: Metformin. The Q asked for “LIKELY” causes. Different sub-types of lactic acidosis. Don’t waste your points by writing “lactic acidosis” twice, when ketoacidosis is another bloody obvious answer.

9. Qvi Predicted serum K This Q stumped a lot of candidates. Please read handout for detailed explanation. In sum, the patient’s current pH is 7.20 (acidaemia), and her measured serum K is 6.0 mmol/L, which is high. The low pH raises the K. The Q asked what would happen to her K IF her pH was corrected to normal – ie 7.40. The answer is that it would drop from 6.0 to something lower (we see this when we treat DKA patients). As most of you identified, the serum K should drop by 0.5mmol/L for every 0.1 rise in pH. Doing the maths, the predicted K is 5.0 mmol/L.

10. Good Luck for the Real Thing!