Answer:

Metabolic Acidosis pH 7.24 HCO3 9

Expected pCO2 = 1.5 x HCO3 + 8 = 21.5

AG = Na – (Cl+HCO3) = 19

Delta gap = AG-12/ 24-HCO3 = 0.46

Expected PAO2 = (713xFiO2) – (pCO2 x 1.25) = 257

A-a gradient 257-115= 142

The ABG shows a compensated metabolic acidosis with mixed HAGMA and NAGMA. There is a severe hyperlactataemia with elevated chloride and glucose. Sodium and potassium are within normal limits. Significantly elevated A-a gradient

The likely cause of the above ABG is due to severe sepsis cause a lactic acidosis. The severely elevated lactate is likely due to hypoperfusion, but other causes should be considered – is the patient on metformin, do they have liver failure? The associated NAGMA could be the result of saline infusion or adrenal insufficiency. The raised A-a gradient is likely due to underlying pneumonia

(ABG obtained from RPH collection of ABG’s – with thanks)