Describe and interpret this blood gas:

History: 85-year-old man found unconscious at home. He has not been seen for several days.

pH 7.21 Na 165 mmol/L
pCO2 36 mmHg K 6.2 mmol/L
HCO3 14 mmol/L Cl 136 mmol/L
Lactate 10.3 mmol/L Glucose  39 mmol/L

Interpretation

 

What is the pH?

7.21 = acidaemia

What is the primary process?

HCO3 14 = metabolic acidosis

Is there compensation?

Expected pCO2 = 1.5 x HCO3 + 8

= 1.5 x 14 + 8

= 29

Actual pCO2 is higher suggesting incomplete compensation or co-existing respiratory acidosis.

Are there other clues to diagnosis?

Anion gap = Na – (Cl + HCO3)

= 165 – (136 + 14)

= 15

Therefore there is a non-anion gap metabolic acidosis.

Corrected Na = Na + (glucose – 5) / 3

= 165 + (39 – 5)/3

= 176.3

Therefore there is severe hypernatraemia.

Electrolyte clues:

Lactate, chloride, potassium and sodium are markedly elevated. Glucose is markedly elevated.


 

Formulation:

Description: This ABG shows an acidaemia secondary to mixed non-anion gap metabolic acidosis and respiratory acidosis. There is hyperglycaemia and severe hypernatraemia with a severe lactic acidosis, elevated chloride and potassium.

Interpretation: In this clinical context, this gas would suggest severe dehydration and a hyperglycaemic, hyperosmolar state. Elevated lactate is normally associated with an elevated anion gap, however the severity of hyperchloraemia is masking this. There is likely to be acute renal failure contributing to the acidosis and elevated potassium. Respiratory compensation is incomplete, probably due to impairment associated with altered mental state. Hypernatraemia and volume deficit must be corrected slowly. Underlying sepsis or other precipitating cause should be sought and treated, however prognosis is likely to be poor.

Additional information: Sepsis with altered conscious state and reduced oral intake for several days, severe dehydration and acute renal failure (creat 400). Patient died in ED soon after presentation.

Blood Gas #3
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