For an adult critically ill patient in the ICU (including those with diabetes, receiving high‑dose steroids or enteral nutrition), what is the recommended glycaemic control approach and the specific sliding‑scale insulin dosing schedule?

Sliding Scale Insulin in the ICU: Not Recommended as Monotherapy

Sliding scale insulin (SSI) should not be used as the primary regimen for critically ill ICU patients; instead, initiate continuous intravenous insulin infusion when blood glucose persistently exceeds 180 mg/dL on two consecutive measurements, targeting 140–180 mg/dL. 1, 2

Why Sliding Scale Insulin Fails in Critical Illness

SSI is a reactive approach that treats hyperglycemia after it occurs, leading to dangerous glucose fluctuations and poor outcomes. 3 The fundamental problem is that SSI provides no basal insulin coverage and responds only to existing hyperglycemia rather than preventing it. 3 This results in:

• Clinically significant hyperglycemia that persists throughout hospitalization 3
• Rapid blood glucose swings that worsen both hyper- and hypoglycemia 3
• Continued use without modification even when control remains inadequate 3

The American Diabetes Association strongly recommends against SSI monotherapy for any hospitalized patient with established insulin needs, stating it should be discontinued immediately. 3

The Correct Approach: Continuous IV Insulin Infusion

Initiation Criteria

Start continuous IV insulin when blood glucose reaches ≥180 mg/dL on two consecutive measurements in any adult ICU patient, regardless of diabetes history, steroid use, or nutritional support. 1, 2 This threshold applies universally to:

• Patients with pre-existing diabetes 2
• Those receiving high-dose corticosteroids 2
• Patients on enteral or parenteral nutrition 2
• Post-surgical and trauma patients 1, 2

The 180 mg/dL trigger is intentionally set lower than the target range to prevent prolonged exposure to harmful hyperglycemia, which causes osmotic diuresis, endothelial dysfunction, immune impairment, and increased infection risk. 1, 2

Target Glucose Range

Maintain blood glucose between 140–180 mg/dL for all critically ill adults once insulin therapy is initiated. 1, 2 This recommendation is based on:

• The NICE-SUGAR trial (6,104 patients), which demonstrated that intensive targets (80–110 mg/dL) increased mortality and severe hypoglycemia 10- to 15-fold compared to conventional targets (140–180 mg/dL) 1, 4
• The 2024 Society of Critical Care Medicine guidelines, which conditionally recommend against lower targets (80–139 mg/dL) to reduce hypoglycemia risk 1

Do not target glucose <140 mg/dL in unselected ICU populations—this increases mortality and severe hypoglycemia approximately four-fold without clinical benefit. 1, 2, 4

Standard Dosing Protocol

Initial infusion rate: 0.1 units/kg/hour of regular insulin via continuous IV infusion. 4 For example, a 70-kg patient would start at 7 units/hour. 4

For severe hyperglycemia >300 mg/dL or DKA: Consider an IV bolus of 0.15 units/kg before starting the continuous infusion. 4 For non-DKA hyperglycemia, the loading dose is optional. 4

Critical safety check: Do not initiate insulin if serum potassium is <3.3 mEq/L; correct hypokalemia first, as insulin drives potassium intracellularly. 4

Monitoring Requirements

Measure blood glucose every 1–2 hours during insulin infusion until values and infusion rates stabilize, then reduce frequency to every 2 hours once stable. 1, 2, 4 The 2024 SCCM guidelines recommend monitoring at ≤1-hour intervals (or continuous glucose monitoring when available) during periods of glycemic instability. 1, 2

Use arterial or venous blood samples rather than capillary measurements, as point-of-care capillary glucose may be inaccurate in critically ill patients with hypotension or poor perfusion. 2

Monitor serum potassium regularly and maintain K⁺ >3.3 mEq/L throughout insulin therapy. 4

Protocol-Driven Care is Mandatory

Use a validated insulin infusion protocol that incorporates explicit clinical decision-support tools (computerized or paper-based) to guide titration. 1, 2 These protocols must have demonstrated:

• Low hypoglycemia rates in validation studies before implementation 1, 2
• Safety and efficacy in the specific ICU population 1, 2
• Clear titration algorithms that adjust insulin based on current glucose and rate of change 1, 2

Protocols with explicit decision-support tools improve glycemic control and lower hypoglycemia incidence compared to protocols lacking such structure. 2 A 2024 scoping review found that most effective protocols were nurse-led and included comprehensive glucose management indicators beyond simple glucose thresholds. 5

Special Population Considerations

Patients with Renal Impairment

Use extra caution in patients with renal failure, as they have significantly higher hypoglycemia risk. 6, 7 In one study, patients with hypoglycemia had estimated creatinine clearance of 69 ± 32 mL/min compared to 117 ± 58 mL/min in those without hypoglycemia (P < 0.01). 6

A modified protocol for renal failure patients achieved mean glucose of 145 ± 10 mg/dL (slightly higher than standard) but eliminated severe hypoglycemia (0% vs. 29%, P = 0.006) and reduced moderate hypoglycemia (32% vs. 76%, P = 0.001). 7

Patients Receiving High-Dose Steroids

Apply the same 180 mg/dL threshold and 140–180 mg/dL target; anticipate higher insulin requirements due to steroid-induced insulin resistance. 2 Do not delay insulin initiation based on anticipated steroid taper.

Patients on Enteral or Parenteral Nutrition

Use the standard continuous IV insulin protocol regardless of nutritional route. 2, 6 A study of 40 trauma patients receiving specialized nutritional support achieved glucose control (70–149 mg/dL) within 5 ± 3 hours using continuous IV insulin, maintaining target range for 19.6 ± 4.7 hours/day with only 0.56% hypoglycemia episodes. 6

Critical Pitfalls to Avoid

Never Use SSI as Monotherapy in ICU Patients

SSI alone results in unacceptable glycemic variability and increased complications. 2, 4 It is particularly dangerous in:

• Patients with type 1 diabetes (risk of diabetic ketoacidosis) 3
• Any patient with established insulin requirements 3
• Critically ill patients with hemodynamic instability 4

Never Use Subcutaneous Insulin in Unstable Patients

Avoid subcutaneous insulin in critically ill patients, particularly during hypotension or shock, due to unpredictable absorption. 2, 4 The 2024 SCCM guidelines conditionally recommend IV insulin over intermittent subcutaneous insulin for acute hyperglycemia management in critically ill adults. 1, 2

Never Delay Insulin Initiation

Do not wait when glucose repeatedly exceeds 180 mg/dL. 2, 3 Persistent hyperglycemia causes progressive harm through osmotic diuresis, immune dysfunction, and infection risk. 1, 2

Never Target Aggressive Glucose Goals

Do not target glucose <140 mg/dL in unselected critically ill patients—this increases mortality and severe hypoglycemia without benefit. 1, 2, 4 Even the recent TGC-Fast trial (9,230 patients) comparing 80–110 mg/dL versus 180–215 mg/dL found no mortality difference, though the higher target group used insulin infusions less frequently. 1

Hypoglycemia Management

Establish a hypoglycemia management protocol before starting insulin and treat any glucose ≤70 mg/dL immediately. 1, 2 Treatment steps:

1. Give 15 g of fast-acting carbohydrate (or IV dextrose if patient is NPO) 3
2. Recheck glucose in 15 minutes 3
3. Repeat treatment if needed 3
4. Reduce the implicated insulin dose by 10–20% immediately if hypoglycemia occurs without an obvious cause 3

Hypoglycemia ≤70 mg/dL is independently associated with increased mortality, and severe hypoglycemia (<40 mg/dL) dramatically increases mortality risk, especially with prolonged or repeated episodes. 2

When SSI Might Be Acceptable (Very Limited Scenarios)

SSI may be considered only in highly selected situations where continuous IV insulin is not warranted: 3

• Mild stress hyperglycemia without pre-existing diabetes 3
• Well-controlled type 2 diabetes (HbA1c <7%) on minimal home therapy with only mild hyperglycemia 3
• Patients who are NPO with no nutritional replacement and only mild hyperglycemia 3
• Patients who are new to steroids or actively tapering steroids 3

None of these scenarios typically apply to critically ill ICU patients requiring mechanical ventilation, vasopressors, or intensive monitoring.

Transition Planning

When the patient stabilizes, can tolerate oral intake, and is ready for ICU discharge, transition to a basal-bolus subcutaneous insulin regimen. 2, 3 Calculate the transition dose from the average insulin infusion rate during the 12 hours before transition. 3

Administer subcutaneous insulin 1–2 hours before discontinuing the IV infusion to ensure adequate overlap and prevent rebound hyperglycemia. 3 Never discontinue IV insulin without prior subcutaneous dosing, especially in patients with type 1 diabetes or DKA. 3