Management of Metformin in Abdominal Surgery

Introduction to Metformin Management

The American College of Cardiology recommends stopping metformin the night before elective abdominal surgery and not restarting it until 48 hours postoperatively, after confirming adequate renal function (eGFR ≥60 mL/min/1.73m²), to prevent metformin-associated lactic acidosis (MALA) 1

Metformin-associated lactic acidosis (MALA) is a rare but life-threatening complication with mortality rates of 30-50%, and abdominal surgery increases this risk due to factors like hemodynamic instability, perioperative fasting, and acute kidney injury 2
The incidence of MALA is low (2-9 cases per 100,000 patients/year), but the risk is substantially increased in patients undergoing abdominal surgery 2

The American Heart Association recommends stopping metformin 12-24 hours preoperatively for patients with normal renal function, allowing for significant drug clearance given its plasma half-life of 6.2 hours 1
For emergency abdominal surgery, the American Society of Anesthesiologists suggests proceeding with surgery without delay, monitoring lactate levels and renal function closely, ensuring adequate fluid resuscitation with balanced crystalloids, and being prepared for hemodialysis if MALA develops 1, 4
Metformin should be restarted 48 hours after surgery only if the patient's eGFR is ≥60 mL/min/1.73m², the patient is eating and drinking normally, and there is no ongoing hemodynamic instability 1

The European Society of Anesthesiology recommends extra caution in patients with baseline renal impairment, elderly patients, those with congestive heart failure, liver disease, or patients on ACE inhibitors, ARBs, or diuretics, as these conditions increase the risk of MALA 2
Despite some evidence suggesting that continuing metformin perioperatively may not significantly raise lactate levels, consensus guidelines from major societies recommend discontinuation due to the catastrophic consequences of MALA 1, 3

Preoperatively, stop metformin the night before elective surgery, check baseline eGFR, ensure adequate hydration, and for emergency surgery, proceed without delay but alert the team to metformin use 1, 3
Intraoperatively, use balanced crystalloids for fluid resuscitation, monitor for signs of tissue hypoperfusion, and maintain mean arterial pressure ≥65 mmHg 4
Postoperatively, check renal function at 48 hours, restart metformin only if criteria are met, and monitor for signs of MALA 1