An 87-year-old nursing home resident is brought to the emergency department with a 2-day history of fever, vomiting, and progressive lethargy. The patient's past medical history is significant for advanced dementia and stroke. Temperature is 38.3 C (101 F), blood pressure is 88/62 mm Hg, and pulse is 120/min and regular. On examination, he is lethargic but arousable. Coarse rhonchi are heard over the right midlung. Laboratory results are as follows: Which of the following is the most likely cause of this patient's increased anion gap?

Question

An 87-year-old nursing home resident is brought to the emergency department with a 2-day history of fever, vomiting, and progressive lethargy.  The patient's past medical history is significant for advanced dementia and stroke.  Temperature is 38.3 C (101 F), blood pressure is 88/62 mm Hg, and pulse is 120/min and regular.  On examination, he is lethargic but arousable.  Coarse rhonchi are heard over the right midlung.  Laboratory results are as follows:   Which of the following is the most likely cause of this patient's increased anion gap?

Quizplus · Accepted Answer

11ec160b_3a17_00be_9249_7793b2d93e4c_MD0001_00 This patient's signs and symptoms (eg, fever, leukocytosis, hypotension, tachycardia) suggest that he is in septic shock. Decreased bicarbonate level and increased anion gap are indicative of anion-gap metabolic acidosis secondary to an elevated lactic acid level. Lactic acidosis may result from overproduction and/or impaired clearance of lactic acid. End-organ hypoperfusion in septic shock impairs tissue oxygenation and decreases oxidative phosphorylation, leading to a buildup of NADH and shunting of pyruvate to lactate following glycolysis. Hepatic hypoperfusion during sepsis also contributes to the accumulation of lactic acid as the liver is the primary site of lactate clearance (via conversion back into glucose). (Choice B) Impaired hepatic gluconeogenesis occurs with several inborn errors of metabolism (eg, pyruvate carboxylase deficiency, glucose-6-phosphatase deficiency) and can result in the buildup of lactic acid. These diseases usually present in infancy with hypoglycemia and lactic acidosis. (Choice C) Impaired renal tubular bicarbonate reabsorption is seen in type 2 (proximal) renal tubular acidosis. Poor bicarbonate reabsorption can occur in a variety of inherited or acquired conditions, including multiple myeloma and drug toxicity (eg, acetazolamide). (Choice D) Increased lipolysis and ketogenesis occur in patients with diabetic ketoacidosis (DKA), which also presents with anion-gap metabolic acidosis. Serum glucose is much higher in DKA (on average >350 mg/dL), and ketones can be detected in blood and urine in these patients. (Choice E) Increased protein breakdown can occur in the setting of chronic metabolic acidosis. However, it is not a direct cause of acidosis. Educational objective: Lactic acidosis in septic shock results from tissue hypoxia, which impairs oxidative phosphorylation and causes shunting of pyruvate to lactate following glycolysis. Hepatic hypoperfusion also contributes to the buildup of lactic acid as the liver is the primary site of lactate clearance.

An 87-Year-Old Nursing Home Resident Is Brought to the Emergency