PH = 7.16, that is severe acidaemia.
HCO3 is low (> 24), So we have metabolic acidosis. Next we need to calculate compensation and anion gap.
To calculate compensation we use Winter’s formula, that is:
Expected pCO2 = 1.5 x HCO3 +8 (+/-2). That is 1.5 x 13.3 + 8 = 27.95. The expected range will be 26 – 30. pCO2 here is 31, that is very close. We can consider it well compensated especially when the gases that we have here are venous. (Even if this patient has very mild additional respiratory acidosis, that won’t change the management).
Anion gap = Na – (Cl +HCO3) = 26.7, So we have HAGMA here.
Because we have HAGMA, we are going to calculate the delta ratio, that is: (AG – 12) / ( 24 – HCO3) = 1.37/ Delta ratio between 0.8 and 2, means we have pure HAGMA here.
Other abnormal finding here is Glucose level of 2.1 (Moderate hypoglycemia).
Usually for the differential diagnosis of HAGMA we use the mnemonic CAT MUDPILES
- C = cyanide, carbon monoxide
- A = alcoholic ketoacidosis and starvation Ketoacidosis.
- T = toluene
- M = methanol, metformin
- U = uraemia
- D = diabetic ketoacidosis
- P = phenformin, pyroglutamic acid, paraldehyde, propylene glycol, paracetamol
- I = iron, isoniazid
- L = lactate
- E = ethanol, ethylene glycol
- S = salicylates
Here, for this case we are going to use LTKR mnemonic.
L – Lactate is within normal range
T – Toxin ???
K – Ketones. The level was 0.4 mmol/L (with in acceptable range).
R – Renal, Urea level was 5.7 mmol/L. (within normal range)
Toxicological cause was initially expected, However, it was hard to find the cause (What toxicological cause can cause hypoglycemia and HAGMA??).
Then, Random cortisol test, revealed low serum cortisol.
*** This patient suffers from NAGMA due to Addison’e disease. But, because of vomiting, patient was losing K and Cl, this led to relative hypochloraemia that affected the AG calculation and led to relatively normal K level.
The condition improved with intravenous hydrocortisone.
Next morning, Synacthen test revealed low cortisol level, that confirmed primary addison’s disease. The patient was discharged on prednisolone and and her condition improved completely.