Question

What acid-base disturbance is expected in a person trekking at high altitude due to hyperventilation?

• A. Metabolic acidosis
• B. Metabolic alkalosis
• C. Respiratory acidosis
• D. Respiratory alkalosis

Hint:

High altitude causes hypoxia-induced hyperventilation, leading to respiratory alkalosis.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks for the primary acid-base change that occurs when an individual breathes rapidly in a low-oxygen environment.
Step 2: Detailed Explanation:

Trigger: At high altitude, the low partial pressure of inspired oxygen (\(P_iO_2\)) leads to hypoxemia. This is sensed by peripheral chemoreceptors (carotid and aortic bodies).

Response: The chemoreceptors trigger a hypoxic ventilatory response, causing the individual to breathe faster and deeper (hyperventilation) to increase oxygen intake.

Impact on CO2: A side effect of this hyperventilation is that it "blows off" excessive amounts of carbon dioxide (\(CO_2\)) from the lungs. This leads to a drop in the partial pressure of arterial \(CO_2\) (\(PaCO_2<35 \text{ mmHg}\)).

Acid-Base Result: According to the carbonic acid equation, a drop in \(CO_2\) leads to a decrease in hydrogen ion concentration and an increase in blood pH. This is defined as Respiratory Alkalosis.

Compensation: Over the next 24–48 hours, the kidneys will begin to compensate by excreting more bicarbonate (\(HCO_3^-\)) to bring the pH back toward normal, but the initial acute disturbance is respiratory alkalosis.

Step 3: Final Answer:
Hyperventilation at high altitude results in a drop in \(PaCO_2\), leading to primary respiratory alkalosis.