How to manage a patient with hyperglycemia (elevated blood sugar) planned for arthroscopy (joint surgery) tomorrow, considering initiating metformin (biguanide oral hypoglycemic agent) today before dinner?

Management of Hyperglycemia Before Arthroscopy

Do not give metformin today—it must be withheld on the day before surgery according to current perioperative diabetes guidelines. 1

Immediate Management Strategy

Blood Glucose Assessment

• A random blood sugar of 194 mg/dL falls within the acceptable perioperative target range of 100-180 mg/dL (though slightly elevated), and does not require postponement of surgery 1
• However, blood glucose >180 mg/dL warrants intervention to optimize glycemic control before the procedure 1
• Check if this patient has known diabetes or if this represents new-onset hyperglycemia, as this affects your management approach 1

Why Metformin Must Be Held

• The American Diabetes Association explicitly states that metformin should be withheld on the day of surgery 1
• The French Society of Anaesthesia recommends stopping metformin the night before surgery 1
• The FDA drug label instructs patients to inform their doctor about metformin use prior to any surgical procedure, as temporary discontinuation may be required 2
• Metformin increases the risk of lactic acidosis in the perioperative setting, particularly with surgical stress, fasting, dehydration, and potential renal hypoperfusion 2

Correct Approach for Tonight

Use Short-Acting Insulin Instead

• Administer rapid-acting or short-acting insulin subcutaneously before dinner to address the current hyperglycemia 1
• A reasonable starting dose is approximately 1 unit of regular insulin or rapid-acting insulin per 10-15 grams of carbohydrate in the meal 1
• Add correctional insulin coverage as needed based on the current blood glucose level 1

Monitoring Protocol

• Check blood glucose again 2-4 hours after dinner to assess response 1
• Recheck fasting blood glucose tomorrow morning before surgery 1
• Target blood glucose 100-180 mg/dL in the perioperative period 1

Tomorrow Morning (Day of Surgery)

Medication Management

• Continue to hold metformin on the day of surgery 1
• If the patient is on any other oral glucose-lowering agents, withhold these on the morning of surgery 1
• If the patient uses basal insulin (NPH or long-acting analog), give half of the NPH dose or 75-80% of the long-acting analog dose 1

Intraoperative Glucose Control

• Monitor blood glucose at least every 2-4 hours while the patient is NPO 1
• Dose with short- or rapid-acting insulin as needed to maintain target range 1
• Consider starting glucose infusion if the patient is on insulin and will be NPO for an extended period, but stop if blood glucose exceeds 297 mg/dL (16.5 mmol/L) 1

Critical Pitfalls to Avoid

Lactic Acidosis Risk

• Never give metformin when the patient will be NPO or undergoing surgery 1
• Surgical stress, dehydration from fasting, and potential hemodynamic changes during arthroscopy all increase lactic acidosis risk with metformin 2
• The FDA warns that patients have a higher chance of lactic acidosis if they have surgery, get dehydrated, or experience stress 2

When to Resume Metformin

• Do not restart metformin for at least 48 hours after major surgery 1
• For arthroscopy (minor-to-moderate surgery), metformin can typically be resumed with the first meal postoperatively once the patient is eating normally and renal function is confirmed to be adequate 1
• Ensure adequate hydration and normal renal function before restarting 1, 2

Additional Considerations

Assess for Undiagnosed Diabetes

• If this is a new finding of hyperglycemia, consider checking HbA1c to assess chronic glycemic control 1
• Patients with HbA1c >8% have increased perioperative risk and may benefit from endocrinology referral for optimization 1

Postoperative Management

• Resume oral intake as soon as possible after arthroscopy 3
• Restart home diabetes medications (including metformin) with the first meal once the patient is tolerating oral intake and adequately hydrated 3
• Continue monitoring blood glucose every 1-2 hours in the immediate postoperative period 3

The key message: Use short-acting insulin tonight instead of metformin, continue to hold metformin tomorrow, and manage perioperative glucose with insulin as needed. 1