25 year old female presents with altered level of consciousness. She has a history of Addisons disease and is on cortisone and fludrocortisone. She has been found by her family with altered conscious state, after going out the night previously.

Below is the patients VBG:

pH 7.2                         Na 140 mmol/l

pCO2 46 mmHg          K 3.6 mmol/l

HCO3 18 mmol/l         Cl 106 mmol/l

B/E -9                          Lactate 3.0 mmol/l

BSL 1.1 mmol/l

Describe and Interpret the VBG

Answer:

Metabolic acidosis pH 7.2 HCO3 18

Compensation – expected PCO2 = 1.5 x HCO3 + 8 = 35mmHg

AG = Na – (HCO3 +Cl) = 16

Delta ratio = Change in AG/ Change in HCO3 = 0.6

The above VBG shows an uncompensated HAGMA, with underlying respiratory acidosis and NAGMA. The VBG also shows a mildly elevated lactate and a life threateningly low BSL. The potassium is on the lower end of normal, is actually likely to be less than 3 given the pH.

The HAGMA in this clinical context can be caused by ketosis – starvation/alcohol related, which might explain the low BSL.  The patient might have also had a seizure from hypoglycaemia leading to a rise in lactate (lactate usually higher in this context) adding to the HAGMA. Toxins should also be considered in this context – toxic alcohols, valproate, massive paracetamol OD, insulin or oral hypoglycaemics.  The underlying respiratory acidosis in this context is likely due to altered GCS and airway obstruction leading to poor ventilation.

The combined NAGMA could be due to underlying Addisons disease in the context of patient being noncompliant with their medication or an acute stress response for example infection or excess alcohol consumption and vomiting the night before. In a true adrenal crisis you would expect hypoglycaemia with a hyperkalaemia and low sodium. This patient has a low potassium and normal sodium. RTA is another possible cause for the NAGMA which would explain the low potassium.