How is sliding scale insulin administered to patients with diabetes, particularly those with type 2 diabetes or unstable glucose levels?

How Sliding Scale Insulin is Administered

Sliding scale insulin should NOT be used as monotherapy in hospitalized patients with established diabetes, but when used, it consists of subcutaneous injections of short-acting or rapid-acting insulin given at scheduled intervals (typically every 4-6 hours or before meals) based on a predetermined dosing table that assigns insulin doses according to current blood glucose levels. 1

Traditional Sliding Scale Method

• Sliding scale insulin traditionally uses regular human insulin administered subcutaneously, with doses determined by checking fingerstick blood glucose at scheduled intervals 1
• The insulin dose is selected from a predetermined scale or table that assigns specific units of insulin to treat glucose values within specified ranges 1
• A simplified approach gives 2 units of short- or rapid-acting insulin for premeal glucose >250 mg/dL and 4 units for premeal glucose >350 mg/dL 2
• Both regular insulin and rapid-acting analogs (lispro, aspart) can be used for sliding scale dosing, though no studies demonstrate superiority of one over the other for correction doses 1

Why This Approach Fails

• Sliding scale insulin is a reactive strategy that treats hyperglycemia after it has already occurred, rather than preventing it 1
• This reactive approach leads to rapid blood glucose fluctuations that exacerbate both hyperglycemia and hypoglycemia 1
• Only 38% of patients achieve adequate glycemic control (mean blood glucose <140 mg/dL) with sliding scale insulin alone, compared to 68% with basal-bolus regimens 1
• Sliding scale regimens prescribed on admission typically remain unchanged throughout hospitalization even when control remains poor 1
• Sliding scale insulin as monotherapy is associated with increased hospital complications including postoperative wound infections, pneumonia, bacteremia, and acute renal failure 1, 3

When Sliding Scale May Be Acceptable

• Patients without pre-existing diabetes who have mild stress hyperglycemia 1, 2
• Patients with well-controlled diabetes (HbA1c <7%) on minimal home therapy who develop only mild hyperglycemia during hospitalization 2
• Patients who are NPO with no nutritional replacement and only mild hyperglycemia 2
• Patients who are new to steroids or tapering steroids 2

The Recommended Alternative: Basal-Bolus Approach

• For hospitalized patients with established diabetes, use scheduled subcutaneous insulin therapy with both basal and nutritional components, supplemented by correction doses rather than sliding scale alone 1
• For insulin-naive patients or those on low doses, start with 0.3-0.5 units/kg/day total daily dose, allocating 50% to basal insulin (once or twice daily) and 50% to rapid-acting prandial insulin (divided before three meals) 1, 2
• For patients with poor oral intake or NPO status, use a basal-plus approach: 0.1-0.25 units/kg/day of basal insulin plus correction doses of rapid-acting insulin 2
• For patients on higher home insulin doses (≥0.6 units/kg/day), reduce the total daily dose by 20% during hospitalization to prevent hypoglycemia 1, 2

Critical Safety Considerations

• Correction-dose insulin (the appropriate term for what was traditionally called "sliding scale") should be an adjunct to scheduled insulin, not monotherapy 1
• If correction doses are frequently required, increase the scheduled basal and prandial insulin doses accordingly rather than continuing to rely on reactive dosing 1
• The basal-bolus approach carries 4-6 times higher hypoglycemia risk than sliding scale insulin alone, requiring vigilant monitoring and hypoglycemia protocols 3
• Lower initial doses should be used for older patients (>65 years), those with renal failure, and those with poor oral intake 1

Intravenous Insulin Alternative

• For critically ill patients, DKA, perioperative care, or post-cardiac surgery, continuous intravenous insulin infusion using regular crystalline insulin is preferred over subcutaneous sliding scale 1
• When transitioning from IV to subcutaneous insulin, calculate the daily dose based on the average insulin infused during the previous 12 hours before transition 1, 3
• Administer subcutaneous basal insulin 2-4 hours before stopping IV infusion, converting at 60-80% of the daily IV infusion dose 3