**Core Concept**
Epidural opioids are used to manage postoperative pain by delivering analgesics directly to the spinal cord. They work by binding to opioid receptors in the spinal cord, which reduces the transmission of pain signals to the brain. This can provide effective pain relief with fewer systemic side effects compared to intravenous opioids.

**Why the Correct Answer is Right**
The correct answer is related to the pharmacokinetics and pharmacodynamics of epidural opioids. Epidural opioids have a slower onset of action compared to systemic opioids due to their need to cross the blood-brain barrier and bind to opioid receptors in the spinal cord. However, their duration of action can be longer due to their slower metabolism and excretion. Additionally, epidural opioids can cause respiratory depression, but this effect is typically delayed compared to systemic opioids.

**Why Each Wrong Option is Incorrect**
**Option A:** This statement is incorrect because epidural opioids can cause respiratory depression, just like systemic opioids. The difference is in the timing and severity of the effect.
**Option B:** This statement is incorrect because epidural opioids can cause urinary retention, but this is not a unique effect compared to systemic opioids.
**Option C:** This statement is incorrect because epidural opioids can cause pruritus, but this is a common side effect of many opioids, not a unique characteristic of epidural opioids.

**Clinical Pearl / High-Yield Fact**
When using epidural opioids, it's essential to monitor the patient's respiratory status closely, especially if they have pre-existing respiratory disease or are taking other sedatives. This is because the delayed onset of respiratory depression can be unpredictable and potentially life-threatening.

**Correct Answer:** B.