Which of the following conditions is least likely to cause respiratory acidosis?

Respiratory acidosis results from an accumulation of carbon dioxide in the bloodstream, typically due to inadequate ventilation. This condition is characterized by decreased blood pH and elevated carbon dioxide levels.

Severe head injury, opioid overdose, and CNS depressant consumption can all lead to respiratory acidosis by impairing the respiratory centers in the brain, leading to hypoventilation and consequently the retention of carbon dioxide. In contrast, severe exercise typically results in the opposite effect where the body compensates for increased carbon dioxide production through increased ventilation. During intense physical activity, the respiratory rate increases to expel excess carbon dioxide produced by the working muscles, which helps maintain normal acid-base balance.

Thus, during severe exercise, the body's physiological response acts to prevent the development of respiratory acidosis by enhancing respiratory function, making it the condition least likely to cause this imbalance.