In chronic respiratory alkalosis, HCO3- falls by _____ mmol/L for every 10 mm Hg decrease in C02

**Core Concept**
Chronic respiratory alkalosis is a condition characterized by a decrease in carbon dioxide (CO2) levels in the blood, leading to an increase in blood pH. This condition can occur due to hyperventilation, which can be caused by various factors such as anxiety, asthma, or chronic obstructive pulmonary disease (COPD). The kidneys compensate for this alkalosis by excreting more bicarbonate (HCO3-) ions.

**Why the Correct Answer is Right**
The correct answer is related to the concept of renal compensation for chronic respiratory alkalosis. In this condition, the kidneys increase the excretion of bicarbonate ions to compensate for the alkalosis. The rate of bicarbonate excretion is proportional to the degree of respiratory alkalosis. Specifically, for every 10 mmHg decrease in CO2, the bicarbonate level (HCO3-) falls by approximately 2-3 mmol/L in the first 24 hours. This is because the kidneys can only compensate for the alkalosis at a rate of 2-3 mmol/L per day.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it suggests a more rapid decline in bicarbonate levels than what is actually observed in chronic respiratory alkalosis.
* **Option B:** This option is incorrect because it suggests a linear relationship between CO2 levels and bicarbonate excretion, which is not accurate.
* **Option C:** This option is incorrect because it suggests a more rapid decline in bicarbonate levels than what is actually observed in chronic respiratory alkalosis.

**Clinical Pearl / High-Yield Fact**
A classic exam trap is to remember that the kidneys can only compensate for chronic respiratory alkalosis at a rate of 2-3 mmol/L per day.

**Correct Answer:** D. 2-3