PH = 7.236, that is moderate acidaemia
HCO3 = 12 (<24), so we have metabolic acidosis.
Next we need to calculate the anion gap and the compensation.
Anion gap = Na – (Cl + HCO3) = 139 – (107 + 12) = 20. So, we have high anion gap metabolic acidosis (HAGMA).
To calculate the compensation we use Winter’s formula. That is expected CO2=HCO3x1.5+8 (+/- 2) = 24 – 28. We have PCO2 of 29. That is very close, also on venous blood gases PCO2 is usually higher than the arterial (Normal arterial PCO2 = 40, while normal venous PCO2 = 48)… Accordingly we can say that this patient have expected PCO2 (However, if there was mild respiratory acidosis or mild respiratory alkalosis it will not change the management of this patient).
Because we have HAGMA, we should calculate the delta ratio to exclude the presence of other metabolic process. That is (AG – 12)/(24-HCO3) = 0.66.
Delta ratio of 0.66 means we have combined NAGMA and HAGMA.
Other abnormal findings:
Cl = 107, that is mild hyperchloraemia.
Serum glucose = 2.6, we have hypoglycemia (Glucose level less than 3.3 mmol/L in fasting, nondiabetic person is considered hypoglycemia).
Lactate = 2.4 mmol/L. That is mild hyperlactataemia. An indication of reduced tissue perfusion.
Ketones = 5.9, that is very high.
So, final conclusion: We have combined HAGMA and NAGMA with severe ketosis and mild hyperchloraemia.
Now we will look through our differential diagnosis list
For 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
This patient has very high Ketones, high lactate and low serum glucose, typical presentation of starvation ketoacidosis.
For the NAGMA we use mnemonic USED CARP
- U = Ureteroenterostomy
- S = Small bowel fistula
- E = Extra chloride
- D = Diarrhea
- C = Carbonic anhydrase inhibitors
- A = Adrenal insufficiency/ Addison’s disease
- R = Renal tubular acidosis
- P = Pancreatic fistula.
This patient has high chloride, which can be the cause of NAGMA. Hyperchloraemia is caused by dehydration in this patient due to reduced water intake.
Read article: Accelerated starvation of childhood. Have I judged ketones?
Robert MILLAR and Anton HARDING