At what blood glucose level should insulin therapy be initiated in critically ill patients in the Intensive Care Unit (ICU)?

When to Start Insulin in ICU Patients

Initiate insulin therapy when blood glucose levels reach ≥180 mg/dL on two consecutive measurements in critically ill ICU patients. 1

Blood Glucose Threshold for Insulin Initiation

The Society of Critical Care Medicine 2024 guidelines provide the most current evidence-based recommendation:

• Start insulin at ≥180 mg/dL (10 mmol/L) for persistent hyperglycemia (defined as two consecutive blood glucose readings at or above this threshold) 1
• This threshold applies to all critically ill adult patients regardless of diabetes history 1
• The trigger threshold is intentionally set lower than the target treatment range to prevent prolonged periods of hyperglycemia 1

This recommendation is consistent across multiple high-quality guidelines, including the 2023 American Diabetes Association Standards 1, the 2017 Surviving Sepsis Campaign guidelines 1, and the 2012 Critical Care Medicine consensus 1.

Target Glucose Range After Insulin Initiation

Once insulin therapy is started:

• Target range: 140-180 mg/dL (7.8-10.0 mmol/L) for most critically ill patients 1
• This moderate target balances glycemic control benefits against hypoglycemia risk 1
• More stringent targets (110-140 mg/dL) may be considered for select populations such as post-cardiac surgery patients, but only if achievable without significant hypoglycemia 1

Rationale for the 180 mg/dL Threshold

The evidence supporting this threshold is compelling:

• Hyperglycemia ≥180 mg/dL is associated with increased mortality, infection rates, and ICU complications 1
• The landmark NICE-SUGAR trial demonstrated that overly aggressive glucose control (targeting 80-110 mg/dL) increased mortality by 14% compared to conventional targets of 140-180 mg/dL 1
• Tight glycemic control (goal <110 mg/dL) resulted in 10-15 fold higher rates of severe hypoglycemia, which independently increases mortality risk 1

Method of Insulin Administration

Use continuous intravenous insulin infusion for critically ill ICU patients 1, 2:

• IV insulin has a short half-life (<15 minutes), allowing rapid titration with changing clinical status 1
• Subcutaneous insulin should be avoided in hemodynamically unstable or critically ill patients due to unpredictable absorption 1
• Implement a validated insulin infusion protocol with explicit clinical decision support 1

Monitoring Requirements

After initiating insulin therapy:

• Monitor blood glucose every 1-2 hours until glucose values and insulin infusion rates stabilize 1
• Once stable, monitoring can be reduced to every 4 hours 1
• Use arterial blood samples rather than capillary samples when arterial catheters are available, as point-of-care capillary measurements may be inaccurate in critically ill patients 1

Population-Specific Considerations

Post-Cardiac Surgery Patients

• May benefit from more stringent glucose control (110-140 mg/dL) to reduce deep sternal wound infections and mortality 1
• Still initiate insulin at ≥180 mg/dL threshold 1

Traumatic Brain Injury Patients

• Use the same ≥180 mg/dL threshold but maintain glucose <150 mg/dL to avoid regional neuroglycopenia 1
• Avoid tight control (<110 mg/dL) as it may worsen neurological outcomes 1

Septic Patients

• Follow the standard ≥180 mg/dL threshold with target range 140-180 mg/dL 1
• Protocolized approach reduces infection rates and improves outcomes 1

Critical Pitfalls to Avoid

Never target glucose <110 mg/dL in general ICU populations - this increases mortality and severe hypoglycemia risk without benefit 1:

• The NICE-SUGAR trial definitively showed harm with intensive glucose control 1
• Hypoglycemia ≤70 mg/dL is independently associated with increased mortality 1
• Severe hypoglycemia (<40 mg/dL) dramatically increases mortality risk, especially with prolonged or repeated episodes 1

Do not use sliding-scale insulin alone as the primary regimen - it results in poor glycemic control and increased complications 1, 3:

• Sliding-scale insulin is reactive rather than proactive 1
• Associated with unacceptable hyperglycemic and hypoglycemic excursions 1

Avoid subcutaneous insulin in unstable ICU patients - absorption is unpredictable during hypotension, shock, or altered perfusion states 1

Do not delay insulin initiation - persistent hyperglycemia >180 mg/dL causes osmotic diuresis, immune dysfunction, and increased infection risk 1

Implementation Strategy

When blood glucose reaches ≥180 mg/dL on two consecutive measurements 1:

1. Evaluate and modify glucose sources - assess nutrition (enteral/parenteral), dextrose-containing fluids, and medications causing hyperglycemia 1
2. Initiate continuous IV insulin infusion using a validated protocol 1
3. Target 140-180 mg/dL for most patients 1
4. Monitor glucose every 1-2 hours until stable 1
5. Ensure potassium monitoring and repletion - do not start insulin if potassium <3.3 mEq/L 3