Respiratory alkalosis is primarily characterized by which of the following?

Respiratory alkalosis is primarily characterized by decreased blood CO2 levels. This condition occurs when there is hyperventilation, leading to an excess loss of carbon dioxide (CO2) from the bloodstream. When CO2 levels decrease, the equilibrium between carbon dioxide and bicarbonate (HCO3-) shifts, resulting in a higher blood pH, which is indicative of alkalosis.

In respiratory alkalosis, the rapid breathing reduces CO2 concentration in the blood, which in turn decreases the formation of carbonic acid and lowers hydrogen ion concentration, causing the pH to rise. Thus, a key clinical feature is the reduction of CO2 in the arterial blood, ultimately leading to the alkalotic state.

Other options either describe conditions unrelated to respiratory alkalosis or are inconsistent with the core characteristics of this disorder. For instance, increased blood CO2 would indicate respiratory acidosis, while increased metabolic HCO3- is more associated with metabolic alkalosis or compensation for acidosis, rather than being a defining feature of respiratory alkalosis. Decreased arterial oxygen levels may occur in some conditions but do not specifically indicate respiratory alkalosis. Hence, the focus on decreased blood CO2 directly highlights the hallmark of this physiological imbalance.