**Core Concept**
The I-brush, also known as an I-gel or I-gel airway, is a type of supraglottic airway device used for maintaining a patent airway during anesthesia or emergency situations. It works by sealing the airway above the vocal cords, allowing for ventilation and protection of the airway.

**Why the Correct Answer is Right**
The I-brush is particularly useful in situations where endotracheal intubation is difficult or impossible, such as in patients with a difficult airway or those who are at risk of aspiration. It is also used in cases where rapid sequence induction of anesthesia is required, as it allows for quick and effective establishment of a secure airway. The I-brush is inserted above the vocal cords, where it forms a seal, allowing for ventilation and protection of the airway.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the I-brush is not typically used for patients with a normal airway. It is reserved for situations where a difficult airway is anticipated or encountered.

**Option B:** This option is incorrect because the I-brush is not a type of endotracheal tube. It is a supraglottic airway device that is used above the vocal cords, rather than being inserted into the trachea.

**Option C:** This option is incorrect because the I-brush is not used for patients who are at risk of cardiac arrest. While it may be used in emergency situations, its primary purpose is to establish a secure airway, not to manage cardiac arrest.

**Clinical Pearl / High-Yield Fact**
The I-brush is a useful device for managing difficult airways, but it requires proper training and technique to insert correctly. It is essential to verify the correct placement of the I-brush before initiating ventilation.

**Correct Answer:** D