Solution to Blood Gas #7

History: A 55-year-old man presents with epigastric pain after drinking alcohol. Below is his venous blood gas on arrival:

pH 7.48 Na 128 mmol/L
pCO2 50 mmHg K 4.1 mmol/L
HCO3 36 mmol/L Cl 79 mmol/L
Lactate 2.2 mmol/L Glucose 36 mmol/L

5-step-approach-to-blood-gas-analysis

What’s the pH?

7.48 = alkalaemia

What’s the primary process?

HCO3 36 = primary metabolic alkalosis

Is there any compensation?

Metabolic Alkalosis: 0.7 plus 20 rule

Expected pCO2 = 0.7 x HCO3 + 20 (+/-5)

= 0.7 x 36 + 20

= 45.2

Actual pCO2 is 50, therefore there is complete respiratory compensation.

Are there any other clues?

Electrolyte clues:

Corrected sodium = Na + (glucose – 5)/3

= 128 + (36 – 5)/3

= 138.3

Therefore corrected sodium is within normal limits.

Potassium is normal.

Chloride is markedly low.

Lactate is mildly elevated.

Glucose is markedly elevated.

What’s the differential diagnosis?

Description: This venous blood gas reveals a maximally compensated, hypochloraemic metabolic alkalosis with overall mild alkalaemia. There is marked hyperglycaemia and pseudohyponatraemia; the sodium corrects into the normal range when the elevated glucose is accounted for. The potassium is normal and lactate is mildly elevated.

Interpretation: In this clinical situation, the metabolic alkalosis is likely to be secondary to volume contraction from hyperglycaemia, or vomiting secondary to abdominal pathology. Endocrine causes (hyperaldosteronism, Cushing’s syndrome, Conn’s syndrome) should also be considered, although the relatively normal sodium and potassium results would argue against this. The severe hyperglycaemia is likely to be secondary to diabetes mellitus without ketoacidosis or coma. This may be type 2 diabetes, but could also be type 1 due to pancreatic failure from chronic alcoholic pancreatitis (in view of the epigastric pain). Management will include assessment of volume status, rehydration with normal saline and administration of insulin.

Additional information: The patient was diagnosed with alcoholic gastritis and dehydration, which resolved with IV fluid supplementation. This was a first presentation of diabetes secondary to chronic pancreatic failure due to chronic alcoholism.

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