Review Question - QID 109469

A 45-year-old Spanish-speaking man with type 1 diabetes mellitus presents to the emergency department with nausea and abdominal pain. He has a medical history of obesity, osteoarthritis, diabetes, diabetic nephropathy, and hypertension. His current medications include insulin, lisinopril, atorvastatin, and ibuprofen. His temperature is 100.5°F (38.1°C), blood pressure is 90/60 mmHg, pulse is 130/min, and respirations are 30/min. His pupils are equal and reactive to light bilaterally. He has poor skin turgor and capillary refill. Jugular venous distention is not detected. Bedside ultrasound reveals a collapsible inferior vena cava with light inspiration. His basic metabolic panel is displayed below:

Serum:
Na+: 119 mEq/L
Cl-: 95 mEq/L
K+: 5.0 mEq/L
HCO3-: not detectable
BUN: 50 mg/dL
Glucose: 960 mg/dL
Creatinine: 1.6 mg/dL
Ca2+: 8.9 mg/dL
PO4-: 3.5 mg/dL

He is admitted to the intensive care unit on a regular insulin drip and 0.9% isotonic saline. His basic metabolic panel 4 hours later is below:

Serum:
Na+: 120 mEq/L
Cl-: 90 mEq/L
K+: 4.2 mEq/L
HCO3-: 2 mEq/L
BUN: 50 mg/dL
Glucose: 680 mg/dL
Creatinine: 1.5 mg/dL
Ca2+: 8.5 mg/dL
PO4-: 3.0 mg/dL

Therapy remains unchanged. 3 hours later, the patient is found to have the ECG in Figure A. What is the most likely cause?