Can I take 30 units of long-acting (insulin) the night before a procedure?

Perioperative Long-Acting Insulin Dosing

Yes, you can take 30 units of long-acting insulin the night before your procedure, but you should reduce the dose to 22.5 units (75% of your usual dose) to minimize the risk of overnight hypoglycemia while maintaining adequate glucose control. 1, 2

Recommended Dose Adjustment

• Reduce your usual long-acting insulin dose by 25% the evening before surgery (in your case, take 22.5 units instead of 30 units). 1, 2
• This 25% reduction strategy has been shown to achieve perioperative blood glucose goals (100-180 mg/dL) with significantly lower risk of hypoglycemia compared to taking the full usual dose. 1
• The alternative recommendation of taking 75-80% of your usual dose (22.5-24 units) is also supported by multiple guidelines and achieves similar outcomes. 1, 3

Critical Timing Considerations

• Take the reduced dose at your usual time the evening before surgery, not earlier or later than your normal schedule. 2
• The overnight period (when you'll be sleeping before your procedure) is when 78% of hypoglycemic episodes occur in patients on basal insulin, making dose reduction essential. 2
• Do not skip the basal insulin entirely—this leads to hyperglycemia and worse perioperative outcomes. 2

Morning of Surgery Instructions

• Do not take any additional long-acting insulin on the morning of surgery. 1, 3
• Hold all oral diabetes medications on the morning of surgery. 1, 3
• If you take SGLT2 inhibitors (empagliflozin, dapagliflozin, canagliflozin), these must be stopped 3-4 days before surgery, not just the morning of. 1, 4

Monitoring Requirements

• Your blood glucose should be checked at least every 2-4 hours while you're fasting (NPO) before and after the procedure. 1, 2
• Target glucose range is 100-180 mg/dL throughout the perioperative period. 1, 2
• Short- or rapid-acting insulin should be available for correction doses if glucose exceeds 180 mg/dL. 1, 2

When Dextrose Infusion May Be Needed

• Dextrose infusion (D5) is not routinely necessary if you take the reduced basal insulin dose as recommended. 2
• However, if your glucose falls below 70 mg/dL or trends downward despite the dose reduction, D5 infusion should be started. 2
• Patients at high risk for hypoglycemia may need prophylactic dextrose infusion even with appropriate dose reduction. 2

Common Pitfalls to Avoid

• The most critical error is taking your full usual dose the night before surgery—this significantly increases overnight hypoglycemia risk. 2
• Do not discontinue your basal insulin completely, as this causes dangerous hyperglycemia. 2
• Ensure your surgical team knows you're on insulin so they can monitor appropriately. 1
• If you're on an insulin pump, different adjustments apply (75-80% of basal rates), so clarify with your team. 1, 3

Evidence Quality Note

The 25% dose reduction recommendation comes from the most recent 2024 American Diabetes Association guidelines and represents the highest quality evidence available for this specific question. 1 Earlier guidelines (2018) recommended more variable reductions (50% for NPH, 60-80% for long-acting analogs), but the current evidence-based approach is more standardized at a 25% reduction. 1