A 45-year-old male patient is brought into the emergency department after being found unconscious. Blood gas analysis reveals the following values: pH 7.28, PaCO2 55 mmHg, HCO3- 24 mEq/L. Which of the following represents the most likely acid-base imbalance?
Metabolic acidosis
Combined respiratory and metabolic acidosis
Respiratory acidosis
Respiratory alkalosis