In acute respiratory acidosis, what typically happens to bicarbonate and compensation compared with chronic respiratory acidosis?

• A. Acute: elevated PaCO2 with pH drop and large bicarbonate increase.
• B. Acute: elevated PaCO2 with pH drop and no bicarbonate change; chronic: elevated PaCO2 with increased bicarbonate due to renal compensation.
• C. Acute: elevated PaCO2 with pH drop and minimal bicarbonate compensation; chronic: elevated PaCO2 with increased bicarbonate due to renal compensation.
• D. Acute: decreased PaCO2.

Answer: (C)

The key idea is how the body compensates for respiratory acidosis over time. When PaCO2 rises and ventilation is inadequate, the pH drops. In the short term (acute), the body's buffering by bicarbonate is minimal because renal adjustments take time to develop. So you see an elevated PaCO2 with a lower pH and only a small (minimal) increase in bicarbonate. Over days to weeks (chronic), the kidneys ramp up bicarbonate reabsorption and new bicarbonate generation, so the HCO3- level rises substantially to help correct the acidosis even though the PaCO2 remains elevated.

Thus the correct understanding is that acute respiratory acidosis shows elevated PaCO2 with a pH drop and minimal bicarbonate compensation, while chronic respiratory acidosis shows elevated PaCO2 with increased bicarbonate due to renal compensation.