**Core Concept**
The question is testing the knowledge of the pharmacokinetics and pharmacodynamics of anesthetics, specifically their onset and duration of action. The correct answer requires understanding the relationship between the route of administration and the speed of onset of anesthesia.

**Why the Correct Answer is Right**
Inhalational anesthetics have a rapid onset of action due to their direct entry into the bloodstream and subsequent diffusion into the brain. This is in contrast to intravenous (IV) anesthetics, which require time to bind to receptors and produce an effect. Among the inhalational anesthetics, desflurane is known for its fastest onset of action, making it ideal for rapid sequence intubation. Its low blood solubility and high vapor pressure contribute to its rapid onset and recovery characteristics.

**Why Each Wrong Option is Incorrect**
* **Option A:** Intravenous anesthetics like propofol have a rapid onset of action, but they are not the fastest. Their onset is still slower than that of inhalational anesthetics like desflurane.
* **Option B:** Topical anesthetics are used to numb a specific area of the body and are not suitable for general anesthesia.
* **Option C:** Regional anesthesia, such as epidural or spinal anesthesia, provides pain relief to a specific region of the body and is not used for general anesthesia.

**Clinical Pearl / High-Yield Fact**
When choosing an anesthetic agent, consider the patient's airway management and the need for rapid sequence intubation. Desflurane's fast onset of action makes it an ideal choice in these situations.

**Correct Answer:** D. Desflurane