A nurse is reviewing the arterial blood gas results of a client with the following values: pH 7.51, HCO3 33 mEq/L, and PaCO2 45 mm Hg. Based on these results, which acid-base imbalance should the nurse identify, and what is the most appropriate initial nursing action?

Metabolic acidosis: prepare to administer sodium bicarbonate if condition worsens.

Metabolic alkalosis: monitor respiratory rate and monitor oxygenation status.

Respiratory alkalosis: administer a sedative to reduce hyperventilation.

Respiratory acidosis: prepare for intubation and mechanical ventilation immediately.