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Microdialysis in the Neurointensive Care Unit: Neurochemical Monitoring in the Severely Injured Brain

 

Microdialysis in the neurointensive care unit reveals markers of cerebral ischemia and cell damage. After traumatic brain injury (TBI ), microdialysis detects early signs of metabolic crisis and ischemia before intracranial pressure rises. After subarachnoid hemorrhage (SAH), a microdialysis catheter in the at-risk brain tissue detects vasospasm hours before clinical signs emerge.

 

Microdialysis allows continuous sampling of the interstitial fluid chemistry of brain tissue. The process uses a microdialysis catheter with a 10mm dialysis membrane at the distal end that functions like a capillary. The catheter takes up substances delivered by the blood (glucose) or released from cells (markers of cerebral metabolism).
These chemical substances from the interstitial fluid
diffuse—at the human brain’s perfusion flow rate of
0.3 l / min—across the membrane into the fluid inside the catheter.

 

The following parameters are monitored in patients after TBI, SAH, and selected strokes:

  • Lactate/Pyruvate ratio: An increase in this marker represents metabolic crisis and energy failure.
  • Glycerol: Cell membrane breakdown and influx of calcium liberates glycerol into interstitial fluid.
  • Brain glucose: Measuring brain glucose assists in managing blood glucose as brain hypoglycemia leads to secondary brain injury while in the ICU .
  • Glutamate: An increase represents cell damage due to opening of neuronal calcium channels.

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•    CFIT
•    TBI Monitoring
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  2010 Saving the Brain Symposium

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"While this type of technology is still in its infancy in humans, it does show promise in treatment and outcome. Our goal within Santa Barbara Neuroscience Institute is to judiciously apply new technologies and to valuate their cost and benefit in terms of outcome."

—Thomas H. Jones

medical director

Santa Barbara
Neuroscience Institute at
Cottage Health System

 

Microdialysis measures these extracellular substances to continuously gauge the biochemistry of neurons and glia and to determine how seriously brain cells are impaired after ischemia, hyperemia, trauma or hemorrhage. This data and analysis may predict outcome in SAH, TBI and stroke patients and can serve as one of the tools used to individualize patient management in the neurointensive care unit. In the future, clinical microdialysis may be utilized to deliver drugs or substances to the brain, as well as to continuously analyze neurotransmitters, cytokines and small proteins.

 

“Microdialysis allows us to examine changes on a cellular and metabolic level after ischemia in a safe and effective manner,” says Alois Zauner, MD, general and cerebrovascular neurosurgeon and neuroendovascular and neurointerventional surgeon on the medical staff of Santa Barbara Neuroscience Institute at Cottage Health System. “It also advances indications of increasing intracranial pressure by about 48 hours and allows us to better titrate treatments for patients.”

 

Capturing Data for Evaluation and Treatment

To optimally employ microdialysis, physicians at Santa Barbara Neuroscience Institute at Cottage Health System work with a highly specialized nursing staff to provide continuous bedside monitoring and manage microdialysis equipment.

 

Microdialysis requires the evaluation of multimodal data with varying ranges for pathology, combined with storing data on an advanced IT system.

 

The Leading Edge of Care for TBI and SAH

Santa Barbara Neuroscience Institute at Cottage Health System is one of 15 institutions in the United States driving clinical aspects of microdialysis for patients after severe traumatic brain injury and subarachnoid hemorrhage or stroke. Intracerebral microdialysis complements other techniques of neuromonitoring that include measurements of brain tissue oxygen tension. Neurointerventions at Santa Barbara Cottage Hospital are part of an international effort to create an electronic database to further research by pooling information about patients with these diseases and conditions and sharing information regarding the effectiveness of diagnoses and treatment utilizing various neuromonitoring systems.

 

“With microdialysis, we are able detect changes that indicate cerebral ischemia and hypoxia, which are responsible for secondary brain damage,” says Alois Zauner, MD, general and cerebrovascular neurosurgeon and neuroendovascular and neurointerventional surgeon on the medical staff at Cottage. “One recent study, for example, associated elevated cerebral glutamate and lactate concentrations with cerebral hypoxia in patients with severe head trauma who were on hyperventilation therapy. We are working toward using this technology to optimize treatment.”

 

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