What is the recommended sliding scale algorithm for a diabetic patient with impaired renal function and currently taking oral hypoglycemic agents, to adjust insulin doses based on blood glucose levels?

Sliding Scale Insulin Should NOT Be Used as Monotherapy

Sliding scale insulin (SSI) as the sole regimen is explicitly condemned by all major diabetes guidelines and should be immediately replaced with a scheduled basal-bolus insulin regimen for any hospitalized patient with established diabetes. 1, 2, 3

Why Sliding Scale Fails

SSI treats hyperglycemia reactively after it has already occurred rather than preventing it, leading to dangerous glucose fluctuations and treatment failures. 2, 3 Only 38% of patients achieve mean blood glucose <140 mg/dL on SSI alone versus 68% with basal-bolus regimens. 2 When used without standing intermediate-acting insulin, SSI is associated with a 3-fold higher risk of hyperglycemic episodes compared to no pharmacologic treatment at all. 4

The Correct Approach: Basal-Bolus Insulin Regimen

For hospitalized patients with diabetes, use a scheduled basal-bolus-plus-correction regimen consisting of basal insulin, prandial insulin before meals, and correction doses for hyperglycemia. 1, 2, 3

Initial Dosing Algorithm

For insulin-naive or low-dose patients:

• Start with total daily dose (TDD) of 0.3-0.5 units/kg/day 1, 2, 3
• Give 50% as basal insulin once daily (glargine or detemir) 1, 2, 3
• Give 50% as prandial insulin divided equally before three meals (rapid-acting analog) 1, 2, 3

For high-risk patients (elderly >65 years, renal failure, poor oral intake):

• Use lower doses of 0.1-0.25 units/kg/day 1, 5, 2

For patients on high-dose home insulin (≥0.6 units/kg/day):

• Reduce TDD by 20% upon hospitalization to prevent hypoglycemia 5, 3

Titration Schedule

Basal insulin adjustment (based on fasting glucose):

• If fasting glucose ≥180 mg/dL: increase by 4 units every 3 days 5
• If fasting glucose 140-179 mg/dL: increase by 2 units every 3 days 5
• Target fasting glucose: 80-130 mg/dL 5

Prandial insulin adjustment (based on 2-hour postprandial glucose):

• Increase by 1-2 units or 10-15% every 3 days based on postprandial readings 5

Correction insulin (supplemental doses):

• Add correction doses of rapid-acting insulin for hyperglycemia using an insulin sensitivity factor 5
• If correction doses are frequently required, increase the scheduled basal or prandial doses accordingly 3

Target Glucose Range

For most non-critically ill hospitalized patients: 140-180 mg/dL 1, 2, 3

For select patients (cardiac surgery, acute ischemic events): 110-140 mg/dL if achievable without significant hypoglycemia 1, 2

Special Considerations for Renal Impairment

For patients with chronic kidney disease stage 5:

• Type 2 diabetes: reduce TDD by 50% 5
• Type 1 diabetes: reduce TDD by 35-40% 5

Renal failure increases hypoglycemia risk due to decreased insulin clearance and impaired gluconeogenesis, requiring more conservative dosing. 5, 2

Managing Oral Hypoglycemic Agents

Metformin:

• Continue metformin unless contraindicated (eGFR <30 mL/min, contrast administration, acute illness with risk of lactic acidosis) 5
• Metformin reduces total insulin requirements and provides complementary glucose-lowering effects 5

Sulfonylureas:

• Discontinue when starting basal-bolus insulin to prevent hypoglycemia 5

Other oral agents (DPP-4 inhibitors):

• Consider discontinuing when initiating basal-bolus insulin 5

When SSI Might Be Acceptable (Rare Exceptions)

SSI as monotherapy might be appropriate only in these limited scenarios: 3

• Mild stress hyperglycemia in patients without pre-existing diabetes
• Well-controlled diabetes (HbA1c <7%) on minimal home therapy with only mild hyperglycemia during hospitalization
• Patients who are NPO with no nutritional replacement and only mild hyperglycemia
• Patients new to steroids or tapering steroids

Critical Pitfalls to Avoid

Never use premixed insulin (70/30) in hospital settings due to unacceptably high rates of iatrogenic hypoglycemia. 5, 3

Never continue SSI as monotherapy even temporarily for patients with established diabetes requiring insulin therapy. 2, 3

Never delay basal insulin adjustments beyond 3 days in stable patients, as 75% of hospitalized patients who experienced hypoglycemia had no basal insulin dose adjustment before the next administration. 5

Recognize overbasalization: When basal insulin exceeds 0.5 units/kg/day without achieving targets, add or intensify prandial insulin rather than continuing to escalate basal insulin alone. 5

Monitoring Requirements

• Check blood glucose every 4-6 hours (before meals and bedtime) 1
• Assess for hypoglycemia (glucose <70 mg/dL) and reduce insulin by 10-20% if it occurs 5
• Reassess insulin regimen daily and adjust based on glucose patterns 1, 2