Q: Patient with history of hypertension and anxiety presented to the hospital with tachypnea.  Patient 

sodium  140meq/l,
potassium 3meq/l, 
chloride  94meq/l and 
HCO₃  34.  

On arterial blood gas, 

ph 7.67
pCO2 30.  

What is the acid base disturbance?

A)  Respiratory alkalosis

B)   Metabolic  alkalosis

C)  Respiratory and metabolic alkalosis

D)  Hyperchloremic non-anion gap metabolic acidosis

Answer: C

Rationale: Patient HCO₃ is high suggestive of metabolic alkalosis.

Patient expected CO₂ should be (pCO₂=HCO₃x0.9+9;34x0.9+9=39.6); 
CO₂ is 30, which is lower than expected pCO₂,
suggestive of mixed respiratory and metabolic alkalosis.