**Core Concept**
In the management of hypovolemia in trauma patients, the initial fluid of choice is crucial to restore circulating volume and maintain adequate perfusion of vital organs. This involves administering a fluid that has a high colloid osmotic pressure, is easily administered, and does not cause significant hemodilution.

**Why the Correct Answer is Right**
The correct answer is a crystalloid solution, specifically 0.9% saline or lactated Ringer's solution. These fluids are chosen because they are isotonic and can expand the intravascular volume without causing significant hemodilution or altering the colloid osmotic pressure. Additionally, they can be easily administered in large quantities, which is essential in the initial management of hypovolemia. The administration of these fluids helps to restore circulating volume, maintain blood pressure, and ensure adequate perfusion of vital organs.

**Why Each Wrong Option is Incorrect**
**Option A:** Blood is not the initial fluid of choice in the treatment of hypovolemia in trauma patients, as it is not easily available and may be contaminated. It is typically reserved for cases where there is significant blood loss and a need for immediate blood transfusion.

**Option B:** Colloids, such as albumin or hetastarch, may be used in the management of hypovolemia, but they are not the initial fluid of choice. This is because they can be expensive and may cause significant hemodilution.

**Option D:** Hypertonic saline is not typically used as the initial fluid of choice in the treatment of hypovolemia in trauma patients. While it can help to increase blood pressure, it can also cause significant hemodilution and may not be suitable for all patients.

**Clinical Pearl / High-Yield Fact**
In trauma patients, the initial fluid of choice should be a crystalloid solution, such as 0.9% saline or lactated Ringer's solution. This is because these fluids are isotonic, can expand the intravascular volume without causing significant hemodilution, and can be easily administered in large quantities.

**Correct Answer:** D. Lactated Ringer's solution.