In a patient with mechanical ventilation, what blood gas result indicates respiratory alkalosis?

Respiratory alkalosis is characterized by a primary decrease in carbon dioxide levels (PaCO2) due to hyperventilation, resulting in an increased blood pH. In this context, the pH value is significant because a high pH, above the normal range of around 7.35 to 7.45, indicates alkalemia.

The given pH of 7.51 clearly falls outside the normal range and suggests alkalosis. To further support the diagnosis of respiratory alkalosis, a low PaCO2 would typically accompany the elevated pH. While neither PaO2 nor HCO3- directly indicate respiratory alkalosis, a PaCO2 of 26 mm Hg would point towards respiratory alkalosis due to its low level, which is consistent with hyperventilation.

However, the question specifically asks for the blood gas result that indicates respiratory alkalosis, and the elevated pH of 7.51 is the most direct indicator of alkalosis itself. Thus, among the choices, the elevated pH is the definitive indicator of a respiratory alkalotic state.