This man presents with typical signs and symptoms associated with small bowel obstruction, presumably secondary to intra-abdominal adhesions. The change in pain pattern from intermittent to persistent, is a concern.
Persistent pain 
can be produced by severe bowel distention or bowel ischemia secondary to strangulation.
Other features of this patient´s presentation suggesting the presence of a complicated bowel obstruction, like:
Fever
Leukocytosis
Elevated serum amylase level Radiograph signs of a high-grade small bowel obstruction
Mechanical obstruction of the bowel produces accumulation of fluid in the bowel lumen, in addition to extravasation of fluid into the peritoneal cavity. Therefure its necessary to restoration of intravascular volume to reestablish organ perfusion.