**Core Concept**
The Whipple procedure, also known as pancreaticoduodenectomy, is a complex surgical operation that involves the removal of the head of the pancreas, the duodenum, the gallbladder, and a portion of the bile duct. This operation is performed to treat various conditions, including pancreatic cancer, ampullary cancer, and chronic pancreatitis. The procedure carries a significant risk of surgical complications.

**Why the Correct Answer is Right**
The most common surgical complication following a Whipple procedure is pancreatic fistula. A pancreatic fistula is an abnormal connection between the pancreas and other organs or the skin, which can lead to the leakage of pancreatic enzymes into the abdominal cavity. This can cause severe abdominal pain, infection, and other complications. The risk of pancreatic fistula is higher in patients who have a history of pancreatitis, diabetes, or other conditions that affect pancreatic function.

**Why Each Wrong Option is Incorrect**
* **Option A:** Bleeding is a potential complication of the Whipple procedure, but it is not the most common complication. Bleeding can occur due to the extensive dissection of tissues and blood vessels during the operation.
* **Option B:** Infection is a possible complication of any surgical procedure, including the Whipple procedure. However, it is not the most common complication of this particular operation.
* **Option C:** Delayed gastric emptying is a complication that can occur after the Whipple procedure, but it is not as common as pancreatic fistula. Delayed gastric emptying is caused by the disruption of the vagus nerve, which regulates digestive function.

**Clinical Pearl / High-Yield Fact**
It is essential for surgeons and anesthesiologists to closely monitor patients after the Whipple procedure and be prepared to manage potential complications, including pancreatic fistula. Early recognition and treatment of complications can significantly improve patient outcomes.

**Correct Answer:** D.