Review Question - QID 215095

A 55-year-old man presents to the emergency department with abdominal pain, nausea, and vomiting for the past 24 hours. He states that he has had these symptoms for many years, but it seems to be occurring more frequently with more severe symptoms during each episode. He is often constipated and has difficulty with bowel movements. He last had a bowel movement earlier in the morning. His past medical history is significant for diabetes, obesity, hyperlipidemia, and hypertension for which he is prescribed lisinopril, metformin, and atorvastatin. He is poorly compliant with his medications. The patient states that he last smoked marijuana 1 month ago. His temperature is 98.9°F (37.2°C), blood pressure is 130/85 mmHg, pulse is 125/min, and respirations are 16/min. Physical exam reveals an obese man with no focal tenderness, guarding or rigidity. He is acutely vomiting. Laboratory studies are ordered as seen below.

Serum:
Na+: 140 mEq/L
K+: 4.0 mEq/L
HCO3-: 27 mEq/L
Blood urea nitrogen (BUN): 58 mg/dL
Creatinine: 1.1 mg/dL
Glucose: 255 mg/dL
Hemoglobin A1c: 13%
Lipase: 100 U/L

Which of the following is the most likely cause of this patient's symptoms?