What is the best approach for managing hyperglycemia in a critically ill patient, considering the use of a sliding insulin scale?

Sliding Scale Insulin in Critically Ill Patients: Evidence-Based Approach

Direct Recommendation

The sole use of sliding scale insulin (SSI) in critically ill patients is strongly discouraged and should be replaced with continuous intravenous insulin infusion protocols targeting a glucose range of 140-180 mg/dL. 1

Why Sliding Scale Insulin Fails in Critical Illness

• Sliding scale insulin is reactive rather than proactive, treating hyperglycemia only after it occurs rather than preventing it, leading to poor glycemic control and increased glucose variability 2, 3
• SSI provides no basal insulin coverage, leaving patients vulnerable to persistent hyperglycemia between correction doses 1
• The American Diabetes Association explicitly states with Grade A evidence that SSI as monotherapy is strongly discouraged in the inpatient setting 1

The Correct Approach for Critically Ill Patients

Initiation Criteria

• Start IV insulin infusion when blood glucose exceeds 180 mg/dL on two consecutive measurements 4, 5
• Discontinue any basal or long-acting subcutaneous insulin immediately when transitioning to IV insulin 5

Target Glucose Range

• Maintain blood glucose between 140-180 mg/dL for the majority of critically ill patients 1, 4, 5
• More stringent targets of 110-140 mg/dL may be considered only in highly selected patients (e.g., cardiac surgery) if achievable without hypoglycemia 1, 4
• Avoid intensive targets <110 mg/dL, as the landmark NICE-SUGAR trial demonstrated increased mortality (27.5% vs 25%) and 10-15 fold higher hypoglycemia rates with tight control 1

Insulin Delivery Protocol

• Use a validated IV insulin protocol (computerized or explicit decision support) that has demonstrated safety and efficacy 1, 5
• Prepare insulin as a continuous infusion at 1 unit/mL concentration after priming tubing with 20 mL waste volume 1
• Start at 0.1 units/kg/hour and adjust based on protocol-driven algorithms 5
• Target glucose decline of 50-75 mg/dL per hour when correcting hyperglycemia 5

Monitoring Requirements

• Check blood glucose every 30 minutes to 1 hour during insulin titration, then hourly once stable 1, 5
• Testing every 4 hours is associated with hypoglycemia rates >10% and is inadequate for safe IV insulin use 1
• Be aware that point-of-care glucose meters may lack accuracy in critically ill patients with anemia, hypoxia, or on vasopressors 1

Critical Safety Considerations

Hypoglycemia Prevention

• Hypoglycemia (<70 mg/dL) is the most dangerous complication and can precipitate seizures, worsen neurological outcomes, and increase mortality 5
• Severe hypoglycemia (<40 mg/dL) occurred in 3.9% with individualized targets versus 2.5% with conventional 140-180 mg/dL targets 6
• Risk factors for hypoglycemia include: interrupted nutrition, low BMI, sepsis, shock, renal replacement therapy, and diabetes mellitus 1

When Subcutaneous Insulin May Be Considered

• IV insulin is mandatory for: type 1 diabetes, hemodynamic instability, and changing clinical status 1
• Subcutaneous insulin may be used only in stable ICU patients after resolution of peripheral edema, off vasopressors, and with consistent nutrition 1
• If transitioning to subcutaneous insulin, administer basal insulin 2-4 hours before stopping IV insulin to prevent rebound hyperglycemia 4

Common Pitfalls to Avoid

• Never use SSI alone - it provides inadequate glycemic control and increases glucose variability 1, 2, 3
• Do not target glucose <110 mg/dL in most critically ill patients - this increases mortality risk 1, 6
• Do not check glucose less frequently than hourly once on stable IV insulin - infrequent monitoring increases hypoglycemia risk 1
• Do not continue long-acting subcutaneous insulin when starting IV insulin in unstable patients 5
• Do not rely solely on point-of-care meters without awareness of their limitations in critical illness (anemia, hypoxia, vasopressor use) 1

Algorithm Summary

1. Glucose >180 mg/dL on two checks → Start IV insulin infusion at 0.1 units/kg/hour 4, 5
2. Target 140-180 mg/dL using validated protocol 1
3. Monitor every 30-60 minutes during titration, then hourly when stable 1, 5
4. Adjust insulin by 1-2 units/hour if glucose remains >180 mg/dL 5
5. Treat hypoglycemia immediately if glucose <70 mg/dL 5
6. Transition to subcutaneous insulin only when stable, off vasopressors, edema resolved, with consistent nutrition 1, 4