Which symptom can be indicative of a primary respiratory acidosis?

Hypoventilation is a key symptom of primary respiratory acidosis because it leads to an accumulation of carbon dioxide (CO2) in the blood, resulting in increased levels of carbonic acid and decreased blood pH (acidosis). In this condition, the respiratory system is unable to effectively eliminate CO2, which is a byproduct of metabolism.

When ventilation is inadequate, CO2 levels rise, causing the blood to become more acidic, and this is the hallmark of respiratory acidosis. Symptoms associated with this condition may include confusion, lethargy, and in severe cases, respiratory failure due to the body's inability to maintain adequate ventilation.

The other options do not directly correspond to primary respiratory acidosis. Hyperventilation typically results in respiratory alkalosis, fluid retention is more associated with various metabolic and renal conditions, and erythema is related to inflammation or an allergic response, not a direct indicator of respiratory acidosis.