Professional and Linguistic Assessments Board (PLAB) Practice Exam

What does ABG indicate for a patient experiencing hyperventilation?

1. Respiratory acidosis

2. Metabolic alkalosis

3. Respiratory alkalosis

4. Metabolic acidosis

The correct answer is: Respiratory alkalosis

In cases of hyperventilation, the body expels carbon dioxide (CO2) at a much higher rate than normal. This rapid loss of CO2 leads to a decrease in its concentration in the blood, which in turn causes a rise in blood pH, resulting in respiratory alkalosis. Respiratory alkalosis is characterized by an increased blood pH and decreased levels of carbonic acid as CO2 levels drop. This condition can often present with symptoms such as light-headedness, tingling in the extremities, and in some cases, muscle cramps due to changes in calcium levels as a result of altered pH. In contrast, respiratory acidosis occurs when there is an accumulation of CO2, often due to hypoventilation, leading to a decrease in pH. Metabolic alkalosis can occur from causes such as excessive vomiting or diuretic use, and would not typically result from hyperventilation. Metabolic acidosis, which might result from conditions like renal failure or lactic acidosis, is also not applicable in this scenario. Thus, for a patient experiencing hyperventilation, the correct indication is respiratory alkalosis.