Heart transplant complicated by metformin induced lactic acidosis

Abstract

Introduction Mild lactic acidosis following heart transplant is a known laboratory finding that generally does not require treatment. However, we encountered a case in which a diabetic patient on metformin underwent a heart transplant and developed a profound rise in lactate which caused a severe anion gap metabolic acidosis and refractory vasoplegia. Methods Case Report. Results A 52 year old man with a past medical history of type 2 diabetes mellitus managed with metformin, chronic kidney disease, and coronary artery disease underwent an LVAD explant and a heart transplant utilizing bicaval anastomosis technique. Twenty minutes after separating from bypass, an arterial blood gas was notable for a lactate of 7.8 mmol/L. Over the next two hours, the patient developed vasoplegia and a severe anion gap metabolic acidosis with a lactate that peaked at 18.0 mmol/L. TEE and surgical visualization agreed that cardiac function was excellent and without evidence of tamponade. The patient's hyperdynamic cardiac function was confirmed by the cardiac output values nearing 14 L/m via Swan-Ganz thermodilution. The patient's preoperative medication history was once more analyzed and metformin induced lactic acidosis was added to our working differential diagnosis. A dialysis line was placed, and continuous veno-venous hemofiltration (CVVH) was initiated in the OR, followed by a downtrend of lactate and improvement in hemodynamics. CVVH was continued in the ICU resulting in resolution of lactemia. Discussion Metformin induced lactic acidosis is rare and a diagnosis of exclusion. We ruled out hypovolemia due to a CVP of 14-15 mmHg and ischemic bowel by benign abdominal exam and normal AST, ALT, amylase, and lipase. Sepsis was considered less likely due to lack of infectious source/fever and maintenance of scheduled antibiotic prophylaxis. We had established that the donor cardiac function was excellent. Due to the unpredictable nature of heart transplant, our patient received metformin within 48 hours of surgery. The patient's known chronic kidney disease, potentially exacerbated by cardiopulmonary bypass, likely contributed to metformin induced lactic acidosis.