A patient with severe secretory diarrhea loses large amounts of bicarbonate-rich intestinal fluid and develops metabolic acidosis. Using pH = 6.1 + log_ 10 dfrac [HCO_3^-] 0.03 times PaCO_2 , which combination of changes is expected as the body compensates?

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MBBS QUESTION #10261

Question 1

A patient with severe secretory diarrhea loses large amounts of bicarbonate-rich intestinal fluid and develops metabolic acidosis. Using $pH = 6.1 + \log_{10}\dfrac{[HCO_3^-]}{0.03 \times PaCO_2}$, which combination of changes is expected as the body compensates?

A primary fall in plasma bicarbonate, with compensatory hyperventilation lowering PaCO2 to partially normalize pH✔️
A primary rise in plasma bicarbonate with an unchanged PaCO2
A primary rise in PaCO2 with a normal bicarbonate level
No change in either bicarbonate or PaCO2, since diarrhea does not affect acid-base status

Correct Answer Explanation

Diarrhea causes direct loss of bicarbonate, producing a primary metabolic acidosis (low HCO3-). The resulting fall in pH stimulates chemoreceptor-driven hyperventilation, lowering PaCO2 as a rapid respiratory compensation that partially restores the HCO3-/PaCO2 ratio and pH toward normal, though full renal compensation takes longer.

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