**Core Concept**
Colloidal plasma expanders are used to treat hypovolemic shock by increasing the intravascular volume, thereby improving cardiac output and tissue perfusion. These agents work by expanding the plasma volume due to their large molecular size, which prevents them from being excreted by the kidneys.

**Why the Correct Answer is Right**
The correct answer, **Dextrans**, is a type of colloidal plasma expander that is commonly used in the treatment of hypovolemic shock. Dextrans are a group of polysaccharides that are derived from the bacterium Leuconostoc mesenteroides. They work by increasing the plasma volume, which helps to improve cardiac output and tissue perfusion. Dextrans are effective in treating hypovolemic shock because they are retained in the intravascular space for a prolonged period, thereby providing sustained volume expansion.

**Why Each Wrong Option is Incorrect**
* **Option A:** **Hypertonic Saline** is a colloidal solution, but it is not a plasma expander. It works by increasing the osmolality of the blood, which helps to draw fluid from the interstitial space into the vascular space. However, it does not provide sustained volume expansion like colloidal plasma expanders.
* **Option B:** **Albumin** is a plasma protein that can be used as a volume expander, but it is not a colloidal plasma expander. It works by increasing the plasma volume, but it is rapidly metabolized and excreted by the kidneys.
* **Option C:** **Gelatin** is another type of colloidal plasma expander, but it is not the correct answer. Gelatin solutions, such as Haemaccel, are used to treat hypovolemic shock, but they are not as effective as dextrans in providing sustained volume expansion.

**Clinical Pearl / High-Yield Fact**
Colloidal plasma expanders, such as dextrans, are effective in treating hypovolemic shock because they are retained in the intravascular space for a prolonged period. This is in contrast to crystalloid solutions, such as normal saline, which are rapidly excreted by the kidneys and provide only temporary volume expansion.

**Correct Answer: D. Dextrans**