Final answer:
The likely diagnosis for the patient with acute epigastric pain, a history of alcohol abuse, and elevated pancreatic enzymes is acute pancreatitis.
Step-by-step explanation:
The diagnosis for the 50-year-old man with acute onset epigastric pain, a history of significant alcohol use, nausea, vomiting, and elevated amylase and lipase is likely acute pancreatitis. This condition is characterized by the inflammation of the pancreas and can be triggered by various factors, including alcohol abuse, gallstones, and hypertriglyceridemia, which the patient already has in his medical history.
The absence of muscle spasm upon percussion of the cheeks rules out other complications, such as parotitis. The aggressive fluid resuscitation is a critical step in the management of pancreatitis, alongside pain control and addressing any underlying causes, such as alcohol intake in this case.