**Question:** A patient is breathing air at sea level and has a respiratory exchange ratio of 1.0. The aerial blood values are: PO2 90 mm Hg ;PCO2 20 mm Hg and pH 7.30. These indicate that the:

**Core Concept:**
The respiratory exchange ratio (RER) is a measure of the balance between oxygen consumption and carbon dioxide production. It is calculated as the ratio of the amount of oxygen consumed (O2) to the amount of carbon dioxide produced (CO2). A RER of 1.0 indicates that the respiratory system is in equilibrium, meaning that the amount of O2 consumed is equal to the amount of CO2 produced.

**Why the Correct Answer is Right:**
In this scenario, the patient is breathing air at sea level, and the RER is 1.0, indicating a balanced respiratory system. The aerial blood values (PO2 90 mm Hg, PCO2 20 mm Hg, pH 7.30) suggest that the respiratory system is functioning normally.

**Why Each Wrong Option is Incorrect:**
A. This option is incorrect because a RER of less than 1.0 would indicate an imbalance between O2 consumption and CO2 production, which is not the case in the given scenario.

B. This option is incorrect because an RER greater than 1.0 would indicate a surplus of CO2 production, which is not supported by the given blood values (PO2 90 mm Hg, PCO2 20 mm Hg, pH 7.30).

C. This option is incorrect because a pH of 7.30 (slightly alkalotic) is not consistent with the given blood values (PO2 90 mm Hg, PCO2 20 mm Hg). A normal pH is around 7.35-7.45, which is not the case in this scenario.

D. This option is incorrect because a PCO2 value of 20 mm Hg is too low, indicating hypoventilation or hypocapnia. A normal PCO2 value is around 40-45 mm Hg.

**Clinical Pearl:**
In clinical practice, it is essential to assess a patient's respiratory status by examining RER, arterial blood gases (PO2, PCO2, pH), and other vital signs (e.g., oxygen saturation, heart rate). This helps in diagnosing respiratory insufficiency, hypercapnia, hypoxia, or alkalosis, and appropriate management strategies can be implemented. Paying attention to these parameters is crucial in determining the patient's respiratory condition and ensuring proper treatment decisions.