Hello Sir. Thanyou for your asking HCM. I read carefull your concern. There are a number of oral glycemic control drugs that should be discontinued before surgery. Metformin usage is discontinued before surgery due to renal function complications that may arise intraoperatively (such as hemodynamic instability or decreased renal perfusion), increasing the risk of lactic acidosis .For that reasons you must not take it. Finally is important to know the level blood glucose or you can used for it finger stic glucose . Before and during operation you are goin to take Insulin, Glucose levels are instead stabilized by a combination of intermediate insulin (NPH) with short-acting insulin twice daily or regular insulin before meals and intermediate-acting insulin at bedtime. Although there currently exists no consensus target range, in general the literature suggests keeping glucose levels between 150 and 200 mg/dL (8 to 11 mmol/L) during surgery. How many unites you must to take? This will be perscrition by endocrinology during operation ,they must to know your wheigt and gluce level ?!?! Suksses in your intervent. Hope i have been helpfull, Kind Regards Dr Klodiana Poshi