## **Core Concept**
The administration of 100% oxygen at the end of anesthesia, after the discontinuation of nitrous oxide and removal of the endotracheal tube, is a common practice. This procedure is primarily aimed at preventing a condition that can arise due to the diffusion of gases out of the blood into the lungs.

## **Why the Correct Answer is Right**
The correct answer, , is related to **diffusion hypoxia**. When nitrous oxide (N2O) is discontinued at the end of anesthesia, it continues to diffuse out of the blood into the lungs. This diffusion dilutes the oxygen and nitrogen in the alveoli, potentially leading to a dilution of the oxygen and thus a temporary reduction in the partial pressure of oxygen in the blood, known as diffusion hypoxia. Administering 100% oxygen helps to prevent this dilution and ensures that the patient maintains an adequate level of oxygenation.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because, although atelectasis can be a concern post-anesthesia, the administration of 100% oxygen is not primarily aimed at preventing atelectasis.
- **Option B:** This option is incorrect as hypoventilation can occur post-anesthesia but the specific administration of 100% oxygen at this juncture is not mainly to prevent hypoventilation.
- **Option C:** This option seems to relate to a plausible concern but is not directly relevant to the immediate administration of 100% oxygen to prevent a specific gas-related dilution effect.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **diffusion hypoxia** is a well-recognized phenomenon that can occur when nitrous oxide is discontinued. Administering 100% oxygen at the end of anesthesia helps prevent this. A classic clinical scenario where this is particularly relevant is in patients who have received nitrous oxide as part of their anesthetic regimen.

## **Correct Answer: D. Diffusion hypoxia**