Severe Lactic Acidosis and Acute Kidney Injury in a 74-Year-Old Woman

Ward round presentation. A 74-year-old woman was admitted from the emergency department with a three-day history of vomiting, abdominal pain, and poor oral intake. Her background includes type 2 diabetes mellitus, hypertension, and heart failure with preserved ejection fraction. Her regular medications are metformin 500 mg twice daily for two years, lisinopril 10 mg once daily for five years, and furosemide 40 mg once daily for the last eight months. She had been taking these as usual until the day before admission when she could not tolerate them due to vomiting. On initial assessment, she was lethargic but rousable. Blood pressure 90/58 mmHg, heart rate 108 bpm, respiratory rate 26/min, temperature 36.9°C. There was no focal abdominal tenderness or peritonism. Mucous membranes were dry. Initial investigations: arterial blood gas showed pH 7.08, bicarbonate 10 mmol/L, lactate 9.0 mmol/L, PaCO2 2.9 kPa. Serum creatinine 240 µmol/L (eGFR 22 mL/min/1.73 m²), urea 28 mmol/L. A urine dipstick was negative for blood and leukocytes. There was no history of recent alcohol excess. A serum metformin concentration drawn on admission was 12.3 mg/L (therapeutic range 0.5-5 mg/L). Her medications were continued on admission. She received 2 litres of intravenous 0.9% sodium chloride over four hours. A repeat lactate after rehydration was 8.2 mmol/L. The clinical impression was lactic acidosis with acute kidney injury. Her oral antihyperglycaemic agent, metformin, was withheld, and supportive care was continued. Over the next 48 hours, her lactate fell to 1.5 mmol/L, and her creatinine improved to 120 µmol/L. She made an uneventful recovery. The differential diagnosis included septic shock, but there was no fever, leukocytosis, or source. The temporal relationship between the withholding of metformin and the improvement in acidosis supports a causal link.