Evaluation of the effect of peri-operative continuation of oral metformin therapy on the incidence of perioperative hyperglycemia compared to standard preoperative cessation of oral metformin therapy 24h before surgery.

Surgical procedures cause metabolic stress and can impair glucose control especially in patients with diabetes mellitus, which often results in peri-operative hyperglycemia. Peri-operative hyperglycemia is associated with impaired wound healing, secondary wound infections, endothelial dysfunction, sepsis, prolonged hospital stay and higher mortality.

Metformin is still the first line treatment in patients with type 2 diabetes mellitus.

Historically it has been stopped before surgery due to fear of hypoglycemia and metformin induced lactic acidosis. However recent studies have suggested that perioperative continuation of metformin might be safe and patients could benefit from more stable preoperative blood sugar levels.

Prospective studies evaluating the benefit of continuing oral metformin therapy in the perioperative period are rare.

The investigators plan to conduct a prospective, randomized-controlled, unblinded clinical trial where patients with type II diabetes mellitus and oral metformin therapy undergoing non-cardiac surgery will be randomized in either an interventional group or a control group. In the interventional group patients will be instructed to continue their regular metformin dose even on the day of surgery, in contrast to the control group, where the patients will be instructed to stop taking metformin 24h prior to surgery.

All other oral anti-diabetic drugs will be paused according to the local anesthesia guidelines.

The investigators plan to evaluate whether or not continuation of metformin can reduce the incidence of perioperative hyperglycemia and whether or not it is associated with elevation of blood lactate levels.

Inclusion Criteria:

• Age 18-99 years
• Diabetes Mellitus Typ 2
• Oral metformin therapy
• Non cardiac-surgery
• Informed consent

Exclusion Criteria:

• Insulin therapy
• Ambulatory surgery
• Preoperative therapy with glucocorticoids (prednisolon or equivalent ≥ 5mg/day for more than 7 days)
• Planned postoperative ICU-stay
• Advanced renal insufficiency (eGFR < 45ml/kg/min)
• Advanced liver cirrhosis or failure (Child-Pugh B or C)
• Alcohol abuse
• Pregnancy,
• Perioperative administration of contrast dye