An Unexpected Complication Due to Metformin Use After Femur Fracture Operation: Metabolic Acidosis Without Lactic Acidosis

A 74-year- old male, who was known to have hypertension, chronic obstructive lung disease, and benign prostate hyperplasia, was evaluated preoperatively in our clinic for a femur fracture. In addition, it was found that the patient was using 1000 mg of metformin per oral due to type 2 diabetes. At the preoperative cardiology evaluation, the ejection fraction was 60% with normal systolic ventricular function. Routine laboratory tests were normal. Metformin was held 24 hours before surgery. Spinal anesthesia was applied with 10 mg bupivacaine and 20 mcg fentanyl. Total blood loss at surgery was 150 cc. After an uneventful surgery, the patient was observed at the surgical postanesthesia care unit. Cardiac and respiratory physical examinations seemed normal but the patient had minimal acidosis and hypoxia in the arterial blood gas analysis. Twelve hours after the operation, compensated high anion gap ( 30 mEq/l) metabolic acidosis emerged, but lactate was normal. The patient's urea and creatinine levels were normal in the control blood tests, and the patient's urine output was above 0.5 ml/kg. Within this period, glucose levels were around 80-140 mg/dl. To overcome metabolic acidosis, bolus intravenous 8.4 % bicarbonate solution was administered. Bicarbonate infusion was started on the continuation of metabolic acidosis and base loss despite the bolus bicarbonate treatment. Since there was no other reason for the metabolic acidosis, metformin usage was considered to cause metabolic acidosis. During this treatment period, despite high anion gap acidosis, there was no lactate elevation. The patient had normal laboratory and hemodynamic values and was discharged from the intensive care unit at postoperative Day 3.