Complications after car accident

[HumanCompanion]

After a complex ligament tear (due to a car accident) surgery, our dog had a fever of 104F for 3-4 days, loss of appetite. Initial blood workup showed band cells, iron deficiency, leukomoid changes and neutrophilic leukocytosis. Second blood test showed no band cells, some improvement in anemia but the rest remained the same. He was put on more oral antibiotics but when fever didn't recede, he was given Ceftriaxone (IV). His pain medication has been tramadol.

He then had bilious vomiting and fresh blood in stool. He's on fluids now.

Vet isn't sure if this is a complication from surgery or if the accident catalyzed another underlying problem. He asked for XRay of the chest and abdomen but those didn't confirm whatever he suspected. He then felt it was pancreatitis (even though the blood in stool was fresh) but tests ruled it out.

Can anyone offer differential diagnosis? Thanks