This VBG was from a young girl with sever gastroenteritis (Vomiting and diarrhoea) for 3 days.

PH = 7.52, that is moderate alkalaemia.

pCO2 = 21 mmHg. So, we have respiratory alkalosis.

Next we look at the compensation. From the history, the condition is acute.

For acute respiratory alkalosis, we expect HCO3 to drop by 2 for every 10 pCO2 less than 40. Accordingly, expected HCO3 should be:

24 – (2 x 19) = 20.2 mmol/L. This patient’s HCO3 is less than expected. (17 mmol/L). SO, we have additional metabolic acidosis.

Next, we need to calculate the Anion Gap to figure out what type of metabolic acidosis this patient has.

Anion Gap is calculated as: AG = Na – (Cl + HCO3) = 13, that is in the HAGMA range.