Blood Glucose Thresholds for Brain Injury

Hypoglycemic Thresholds That Cause Brain Injury

Severe hypoglycemia at ≤40 mg/dL (2.2 mmol/L) is independently associated with increased mortality and can cause permanent brain injury or death 1, 2, 3, 4
Symptoms typically develop when blood glucose falls below 50-60 mg/dL (2.8-3.3 mmol/L), including confusion, slurred speech, and altered consciousness 5
Untreated severe hypoglycemia can lead to seizures, status epilepticus, unconsciousness, permanent cognitive dysfunction, and death 5
Blood glucose ≤70 mg/dL is associated with increased mortality in critically ill patients 6, 3, 4
In brain-injured patients, even brief episodes of severe hypoglycemia carry greater risk than in patients with normal brains 6, 4

Treating moderate to severe hyperglycemia (>180-200 mg/dL or >10.0-11.1 mmol/L) is reasonable to improve outcomes in intracerebral hemorrhage 1, 2
In trauma patients, blood glucose ≥150 mg/dL should trigger insulin therapy initiation 6, 3, 4

Target serum glucose between 8-10 mmol/L (144-180 mg/dL) for TBI patients 7
Maintain blood glucose absolutely <180 mg/dL using protocols that achieve low rates of hypoglycemia 6, 3
Seven randomized controlled trials found that strict glucose control did not improve neurological outcome or mortality in TBI but increased hypoglycemia risk 7
Monitor serum glucose to reduce risk of both hyperglycemia and hypoglycemia 1, 2
Treat hypoglycemia <40-60 mg/dL (2.2-3.3 mmol/L) to reduce mortality 1, 2
Treat hyperglycemia >180-200 mg/dL (10.0-11.1 mmol/L) to improve outcomes 1, 2

Both extreme hypoglycemia and hyperglycemia create a U-shaped mortality curve in brain-injured patients 6, 4
Overly aggressive glucose control attempting to achieve tight targets (80-110 mg/dL) increases hypoglycemia risk without improving outcomes 7, 1, 2
Tight systemic glycemic control can cause regional cerebral neuroglycopenia even when serum glucose appears adequate 7, 4
Cerebral microdialysis studies show that systemic glucose 80-110 mg/dL can be associated with critically low brain interstitial glucose 7, 1, 2
Regular blood glucose monitoring from venous or arterial blood samples is essential in brain-injured patients 7
Use protocols that achieve low rates of hypoglycemia (≤70 mg/dL) rather than aggressive targets 6, 3

Hyperglycemia after traumatic brain injury is a stress-related response induced by counter-regulation hormones and insulin resistance, and is associated with increased mortality, poor neurological outcomes, and worsening of secondary brain injury 8, 9
Hyperglycemia with serum glucose >11 mmol/L is an independent risk factor for mortality, infection, and prolonged ICU stays in TBI patients 8, 9

Using cerebral microdialysis, low glycemic control is associated with decreased interstitial brain glucose concentration, and triggers elevations of interstitial brain concentrations of lactate, glutamate, and lactate/pyruvate ratio, suggesting a cerebral energy crisis 9, 10
A randomized crossover study with TBI patients showed that strict glucose control resulted in increased cerebral metabolism and elevation of markers of energy crisis compared to a more liberal strategy 9, 10

Multiple observational studies have demonstrated that hyperglycemia after TBI is associated with increased risk of mortality and poor neurological outcomes 8, 9
Current guidelines strongly recommend maintaining serum glucose concentration between 8 mmol/L and 10-11 mmol/L in severe TBI patients, with a Grade 1+ (strong positive recommendation) and strong agreement among experts 8, 9, 11
Regular monitoring of blood glucose concentrations from venous or arterial blood samples is essential, and both hypoglycemia and hyperglycemia should be avoided, as strict control of serum glucose did not improve neurological outcome or mortality but increased the risk of hypoglycemia 9, 10, 12
Avoid strict glycemic control (<6 mmol/L) as it can lead to hypoglycemic episodes that are particularly harmful to the injured brain 9, 10, 12