Which finding indicates respiratory acidosis?

Which finding indicates respiratory acidosis?

• A. PaCO2 > 45 mmHg
• B. HCO3- < 22 mEq/L
• C. pH < 7.35
• D. PaCO2 < 35 mmHg

Answer: (A)

Respiratory acidosis occurs when ventilation is inadequate and CO2 builds up, forming more carbonic acid and lowering the blood pH. The clearest indicator of this respiratory problem is an elevated arterial CO2 (PaCO2 above 45 mmHg). Among the options, a PaCO2 greater than 45 directly shows CO2 retention driving acidity. While a low pH confirms acidosis, it doesn’t specify the cause. A low bicarbonate would suggest a metabolic process rather than a primary respiratory issue, and a PaCO2 below 35 mmHg points to respiratory alkalosis from hyperventilation, not acidosis. In acute respiratory acidosis, CO2 rises and pH drops; in chronic cases, the kidneys partially compensate by increasing bicarbonate, which can blunt pH changes.

Respiratory acidosis occurs when ventilation is inadequate and CO2 builds up, forming more carbonic acid and lowering the blood pH. The clearest indicator of this respiratory problem is an elevated arterial CO2 (PaCO2 above 45 mmHg). Among the options, a PaCO2 greater than 45 directly shows CO2 retention driving acidity.

While a low pH confirms acidosis, it doesn’t specify the cause. A low bicarbonate would suggest a metabolic process rather than a primary respiratory issue, and a PaCO2 below 35 mmHg points to respiratory alkalosis from hyperventilation, not acidosis. In acute respiratory acidosis, CO2 rises and pH drops; in chronic cases, the kidneys partially compensate by increasing bicarbonate, which can blunt pH changes.