**Core Concept**
Epidural anesthesia involves injecting a local anesthetic into the epidural space surrounding the spinal cord, providing regional analgesia. The effects of epidural anesthesia are influenced by various factors, including the type of anesthetic used, the dosage, and the patient's individual response.

**Why the Correct Answer is Right**
The correct answer, **A. bd**, includes two key points: **b) C/I in coagulopathies** and **d) Venous return decreases**. Epidural anesthesia is contraindicated in patients with coagulopathies due to the risk of hematoma formation, which can lead to nerve compression and permanent damage. Additionally, epidural anesthesia can cause a decrease in venous return due to the compression of the epidural veins, leading to a decrease in cardiac preload and potentially causing hypotension.

**Why Each Wrong Option is Incorrect**
**Option A:** a) Effects start immediately is incorrect because the onset of epidural anesthesia can take anywhere from 15 to 30 minutes, depending on the type of anesthetic used and the individual patient's response.

**Option B:** Given in subarachnoid space is incorrect because epidural anesthesia is administered in the epidural space, not the subarachnoid space (which is where spinal anesthesia is given).

**Clinical Pearl / High-Yield Fact**
It's essential to carefully assess patients for coagulopathies before administering epidural anesthesia, as this can significantly reduce the risk of complications.

**Correct Answer:**
✓ Correct Answer: A. bd