PHOENIX, ARIZ. — Intensive glycemic control—while beneficial for ICU patients in general—may be harmful to patients with traumatic brain injury, Paul M. Vespa, M.D., warned at a meeting sponsored by the Society of Critical Care Medicine.
“When you use intensive glycemic control, you see a higher incidence of abnormal markers in the microdialysis. We don't know yet whether that's going to be bad for the brain,” said Dr. Vespa, director of the neurocritical care program at the University of California, Los Angeles.
He urged monitoring of microdialysis values to prevent adverse effects in traumatic brain injury (TBI) patients receiving intensive glycemic control.
Dr. Vespa reported on a small, prospective study that used the Kety-Schmidt method to measure glucose metabolism in 50 patients with TBI who received intermittent subcutaneous insulin (goal of 100–160 mg/dL). Positron emission imaging (PET) was used to measure glucose and oxygen metabolism in 20 patients given continuous insulin infusions (goal of 90–120 mg/dL).
“There was no relationship between serum glucose and PET-derived measure of whole brain glucose metabolism,” Dr. Vespa said.
A microdialysis catheter was used for constant monitoring of the injured area of the brain during continuous insulin infusions in the 15 patients with baseline hyperglycemia. Ten responded with a 70% reduction on average in microdialysis glucose.
In responders, microdialysis values fell below 2 mmol/L 31% of the time, according to Dr. Vespa. In this same group, lactate/pyruvate ratios rose above 40 about 60% of the time. Nonresponders had low microdialysis glucose 10% of the time and high lactate/pyruvate ratios 23% of the time.
Dr. Vespa said these values put patients in a “danger or distress range” that has been associated with poor outcomes in published studies. These patients also had elevated lactate/pyruvate ratios, which he described along with low brain glucose as “surrogate markers of brain distress.”
His group is continuing its investigation but with a keen eye on microdialysis values.
“When we are treating the heart with a medication, we monitor the heart, we monitor cardiac enzymes, et cetera. When we treat the brain, most people are not monitoring the brain,” he said.
“This is a study that shows when we take a general medical critical care practice like insulin therapy and apply it to the brain-injured patient, we should be monitoring that patient's brain.”
Michael Diringer, M.D., chair of the SCCM session on clinical neuroscience research, praised Dr. Vespa for raising a red flag, but questioned whether the drop in microdialysis glucose is harmful in the absence of a change in glucose metabolism. Glucose levels went down in the blood, but the brain was using the same amount of glucose.
“So I don't know what that fall in the microdialysis means. It may not mean anything,” said Dr. Diringer of Washington University School of Medicine in St. Louis.
Dr. Vespa noted that in general, intensive insulin therapy has been shown to be beneficial for other types of critical care patients, who often develop hyperglycemia and insulin resistance although they were not diabetic prior to their illness.