Q&A Medicine>>>>>Nephrology
Question 15#

As part of a study, a healthy volunteer with no medical problems is asked to hyperventilate for a few minutes, after which laboratory values are drawn.

Which of the following findings would you expect?

A. (A)
B. (B)
C. (C)
D. (D)

Correct Answer is B

Comment:

 pH 7.55, Anion gap normal, HCO₃ 22 mEq/L, PaCO₂ 25 mmHg. (A) Acute hyperventilation will produce a respiratory alkalosis, decreasing serum PaCO₂ and increasing the pH. (C) The serum bicarbonate will not decrease very much with acute respiratory alkalosis; the formal calculation for predicting the decrease in HCO₃ is: 0.2 × ΔPaCO₂ (predicts a drop in HCO₃ of 3.2 mEq/L; 14 mEq/L is therefore too low). (D) The presence of an anion gap indicates a metabolic acidosis, which would not be present as a result of hyperventilation.