A. Jejunojejunal leak: This is the most likely diagnosis given the symptoms of abdominal pain, distension, and the presence of serous fluid in the drains. A leak from the jejunojejunal anastomosis can lead to these symptoms, especially if it occurs early in the post-operative period.

B. Duodenal blow out: Although less common than a jejunojejunal leak, a duodenal blowout (also known as a duodenal stump leak) is a possible complication after a total gastrectomy. It can present with similar symptoms, including abdominal pain and distension, and the presence of fluid in the drains.
C. Afferent loop syndrome: This condition occurs when there is an obstruction of the afferent limb of the small intestine, which can happen after a gastric bypass or total gastrectomy. Symptoms can include abdominal pain, distension, and vomiting, making it a plausible diagnosis in this scenario.

Infection or Sepsis: Although not explicitly listed among the options, infection or sepsis is a critical diagnosis that must not be missed. The patient's fever (T 38.5) and tachycardia (P 98) could indicate an infectious process, which could be related to any of the surgical complications listed or a separate issue altogether.
Bleeding: Post-operative bleeding is another condition that could present with abdominal pain and distension. It is crucial to consider this diagnosis, especially if the patient shows signs of hemodynamic instability.

D. Post gastrectomy syndrome: This is a broader term that encompasses various symptoms that can occur after gastrectomy, including dumping syndrome, diarrhea, and malabsorption. While it's a possible long-term complication, it's less likely to present acutely in the immediate post-operative period with the symptoms described.
Other rare complications such as intestinal obstruction, pancreatitis, or cholecystitis could also be considered but are less directly related to the specific symptoms and surgical history provided.