Describe and interpret this venous blood gas.

History: 24-year-old woman with nausea and vomiting.

pH 6.98 Na 134 mmol/L
pCO2 19 mmHg K 6.3 mmol/L
HCO3 4 mmol/L Cl 107 mmol/L
Urea 12.9 mmol/L Glucose 45 mmol/L
Lactate 1.8 mmol/L

Interpretation

 

What is the pH?

6.98 = severe acidaemia

What is the primary process?

HCO3 4 = primary metabolic acidosis

Is there compensation?

Expected pCO2 = 1.5 x HCO3 + 8

= 1.5 x 4 + 8

= 14

Therefore almost complete respiratory compensation.

Are there other clues to diagnosis?

Anion gap = Na – (HCO3 + Cl)

= 134 – (4 + 107)

= 23

Therefore there is an elevated anion gap.

Delta gap = (Anion gap – 12) ÷ (24 – HCO3)

= (23 – 12) ÷ (24 – 4)

= 0.55

Suggests a coexisting non-anion gap acidosis.

Corrected Na = Na + (glucose – 5)/3

= 134 + (45 – 5)/3

= 147.3

Therefore there is mild hypernatraemia.

Calculated osmolality = (2 x Na) + urea + glucose

= (2 x 134) + 12.9 + 43

= 323.9 mOsm/L

Therefore there is increased osmolality.

Electrolyte clues:

Lactate is slightly elevated, glucose is markedly elevated. Potassium is elevated. Chloride is within the normal range. Urea is elevated.


 

Formulation:

Description: This venous blood gas shows a severe acidaemia secondary to combined high anion gap and non-anion gap metabolic acidosis with almost complete respiratory compensation. There is increased osmolality and mild hypernatraemia. Urea is elevated, potassium is elevated, glucose is markedly elevated.

Interpretation: In this clinical context, this VBG is consistent with severe diabetic ketoacidosis. There is significant volume loss/dehydration with elevated urea and sodium. Management includes resuscitation with normal saline, followed by commencement of insulin infusion and gradual rehydration. Hyperkalaemia in the context of acidosis will normalise with correction of the pH, and potassium replacement is likely to be required as acidosis resolves.

Blood Gas # 12
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