A 52-year-old woman with type 2 diabetes mellitus and cirrhosis presents to the emergency department with altered mental status, jaundice, and ascites. Laboratory findings: serum lactate 6.8 mmol/L (normal 0.5–2.2), blood glucose 178 mg/dL, serum albumin 2.1 g/dL, INR 2.8, and ammonia 95 µmol/L (normal 11–35). Arterial blood gas shows pH 7.28, HCO~3~^−^ 14 mEq/L. Which pathophysiologic mechanism best explains the elevated lactate in this patient?