1. SAQ 25 Feedback Don Liew December 2015

2. Stem A previously well 55 year-old woman presents with … severe vomiting for 5 days. Observations: HR 110 BP100/60 Temp36.8 deg C

3. Thoughts on Stem Vomiting for 5 days should lead to dehydration. Expect loss of H+ and Cl- ions unless sufficiently replaced. Signs of hypovolaemia, with possible shock, so compensation not sufficient. No fever lessens but does not diminish possibility of sepsis. Previously well, so no pre-existent illnesses (that is, before the last 5 days). There are mechanisms in place to cause metabolic derangements: acidosis AND alkalosis. Could they currently co-exist??

4. Prop (Venous Gas) pH7.23 pO240 pCO222 HCO39 (wow!) Na140 K3.4 Cl77 (wow again!)

5. Thoughts on Prop Can identify profound met acidosis with high AG and resp compensation readily. K is very low, esp with low pH. HAGMA likely due to shock and probable acute (pre)renal failure. Co-existent met alkalosis?? I expect it, esp given the stem and severe hypochloraemia, so a Delta Ratio of >2.0 is expected! Hope they ask about this.

6. Q1. What is Primary Disturbance? Low pH and low HCO3 means acidaemia from primary metabolic acidosis. Low pCO2 reflects attempts at respiratory compensation.

7. Q2. Calculate the AG AG = Na – Cl – HCO3 = 140 – 77 – 9 = 54 Reference range is 12 or less, so this is HAGMA. K may be used, in which case calculated AG is 57.4, and the reference range is 16. Still HAGMA, of course.

8. Q3. Is there adequate compensation? In primary met acidosis, expected pCO2 = 1.5 x HCO3 + 8, +/- 2 =13.5 + 8 +/- 2 =21.5 +/- 2 = 19.5 to 23.5 Answers from 19 to 24 accepted. Precision is impossible, given assumptions. Moreover, this is a venous sample. Calculated pCO2 is 22, meaning the respiratory compensation is adequate.

9. Q4. What is the Delta Ratio? Glad they asked! Delta Ratio equals Addition of acid / Loss of HCO3 = (Measured AG – Reference AG) / (Reference HCO3 – Measured HCO3) = (54 – 22)/(24 – 9) = 42/15 = 2.8

10. Q5. What does DR tell us? DR > 2.0, meaning concurrent metabolic alkalosis, just as we expected from stem and serum Cl! That is, the patient has hypochloraemic metabolic alkalosis from protracted vomiting, leading to excessive loss of HCl. NB: She is previously healthy, so any comments about pre-existent disease such as chronic CO2 retention and pre-existent high HCO3 are silly.

11. Q6. Provide a Unifying Explanation Triple derangement from decompensated hypovolaemia secondary to vomiting. 1.Severe metabolic acidosis from tissue hypoperfusion (ie shock). HAG likely from lactic acidosis and pre-renal failure. 2.Concurrent hypochloraemic met alkalosis from loss of gastric HCl. 3.Respiratory alkalosis from compensatory hyperventilation as response to item 1.

12. Borderline Mark All of Qs 1, 2 and 3. One mark each from Qs 4 and 5. Makes total of 7, out of 11.

13. Thanks to Rachel, Jon and crew at Monash for yet another great product. Good luck everyone, for the real thing!