Peri‑operative Management of Metformin to Prevent Metformin‑Associated Lactic Acidosis

1. Core Recommendation

2. Timing of Discontinuation by Surgical Type

2.1 Elective Major Surgery

2.2 Elective Minor / Ambulatory Surgery

3. Risk of Metformin‑Associated Lactic Acidosis (MALA)

4. High‑Risk Patient Factors Requiring Extra Caution

5. Criteria for Restarting Metformin

5.1 Minor / Ambulatory Surgery

6. Pre‑operative Assessment

7. Intra‑operative Management

8. Post‑operative Monitoring

9. Peri‑operative Glucose Management While Metformin Is Held

Perioperative Metformin Management

Introduction to Metformin Management

• The American College of Physicians recommends stopping metformin the night before elective surgery and not restarting until 48 hours after surgery, only after confirming adequate renal function (eGFR ≥60 mL/min/1.73m²) 4, 5

Timing of Discontinuation

• For patients undergoing elective surgery, discontinue metformin the evening before surgery for patients with normal renal function, allowing adequate clearance given metformin's 6.2-hour plasma half-life 4, 5
• Proceed with surgery without delay if metformin cannot be stopped in advance, and alert the surgical and anesthesia team to metformin use 4, 5

Rationale for Withholding

• Metformin-associated lactic acidosis is rare (2-9 cases per 100,000 patients/year) but carries 30-50% mortality 4, 5
• Surgery increases the risk of metformin-associated lactic acidosis through multiple mechanisms: hemodynamic instability, perioperative fasting, tissue hypoperfusion, acute kidney injury, and volume depletion 4, 5

High-Risk Surgical Situations

• Metformin must be stopped for procedures involving iodinated contrast administration, especially if the patient has a history of liver disease, alcoholism, heart failure, or intra-arterial contrast use 6
• Metformin should also be stopped for major abdominal surgery due to the higher risk of hemodynamic instability and acute kidney injury 5

Criteria for Restarting Metformin

• Do not restart metformin until 48 hours post-surgery, and only if the patient has an eGFR ≥60 mL/min/1.73m², is eating and drinking normally, and has no ongoing clinical instability 4, 5

Special Populations Requiring Extra Caution

• Patients with baseline renal impairment (eGFR 30-60 mL/min/1.73m²) require more conservative management, and metformin should be stopped at least 24 hours before the procedure 5
• Patients on ACE inhibitors, ARBs, or diuretics are also at higher risk of metformin-associated lactic acidosis and require closer monitoring 5

Practical Algorithm Summary

• Preoperatively, stop metformin the night before elective surgery, check baseline eGFR, and ensure adequate hydration 4, 5
• Intraoperatively, use balanced crystalloids for fluid resuscitation and maintain adequate perfusion (MAP ≥65 mmHg) 5
• Postoperatively, check renal function at 48 hours and restart metformin only if eGFR ≥60 mL/min/1.73m², patient eating/drinking normally, and no clinical instability 4, 5