## Core Concept
Total Parenteral Nutrition (TPN) is a method of providing essential nutrients to the body through intravenous (IV) infusion when a patient cannot or should not receive feedings or fluids by mouth. Complications associated with TPN can be metabolic, infectious, or mechanical in nature.

## Why the Correct Answer is Right
The most common complication associated with TPN is hyperglycemia, which occurs due to the infusion of glucose-containing solutions that can exceed the body's ability to produce insulin or effectively utilize insulin. This is particularly problematic in patients with diabetes mellitus or those who are under stress, as they may have insulin resistance. Hyperglycemia can lead to osmotic diuresis, dehydration, and electrolyte imbalances.

## Why Each Wrong Option is Incorrect
- **Option A:** While infections, particularly central line-associated bloodstream infections (CLABSIs), are a serious complication of TPN, they are not the most common metabolic complication but rather a significant infectious risk.
- **Option B:** Electrolyte imbalances are common but are often considered secondary to the metabolic complications like hyperglycemia. They can occur due to the composition of the TPN solution or the patient's underlying condition.
- **Option C:** Malnutrition is actually what TPN aims to prevent or treat, not a complication of TPN itself.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **hyperglycemia** is a frequent complication of TPN, particularly in the initial phases of therapy. Monitoring blood glucose levels regularly and adjusting the TPN formulation as needed can help mitigate this risk.

## Correct Answer Line
**Correct Answer: D. Hyperglycemia**