**Core Concept**
In the context of water intoxication, also known as water poisoning or hyponatremia, the underlying principle is the excessive ingestion of water, leading to an imbalance in sodium levels in the body. This condition can be particularly dangerous in surgical patients, as it can cause swelling of brain cells and potentially lead to seizures, coma, or even death.

**Why the Correct Answer is Right**
The most common cause of water intoxication in surgical patients is the administration of hypotonic IV fluids, specifically 0.45% saline or lactated Ringer's solution. These solutions contain a lower concentration of sodium than the body's natural fluids, which can dilute the sodium levels in the blood and cause water to move into cells, leading to swelling. This is particularly concerning in patients undergoing surgery, as they may be unable to effectively regulate their fluid balance.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specify a type of fluid that is commonly associated with water intoxication.

**Option B:** This option is incorrect as it refers to a condition where the body loses excess water, which is the opposite of water intoxication.

**Option C:** This option is incorrect as it refers to a medication that is not directly related to the development of water intoxication.

**Clinical Pearl / High-Yield Fact**
A key point to remember when managing surgical patients is that hypotonic IV fluids can cause a significant shift of water into cells, leading to hyponatremia. It is essential to carefully monitor fluid balance and sodium levels in these patients to prevent this potentially life-threatening complication.

**Correct Answer: D. Hypotonic IV fluids.**