Cerebral Microdialysis

Cerebral microdialysis

  • Microdialysis probes
    • typically placed in subcortical white matter via tunneling technique or a bolt
      • Tunneling more accurate targeting of penumbral or peri-lesional tissue
      • Bolting can be performed at bedside, placed at Kocher’s point, which may limit penumbral targeting
    • position probes in key area of interest
  • Artificial CSF dialysate perfused at tandard rate (0.3 μL/min) through the microdialysis catheter (10 mm membrane)
  • Molecules below cutoff size (10,000–20,000 daltons) diffuse from extracellular space into perfusion fluid – collected and analyzed at bedside (capillary micronutrient, drug delivery, neuronal and glial metabolites)
  • most commonly measured interstitial brain analytes
    • lactate
    • pyruvate
    • (lactate to pyruvate ratio)
      • indicates energy failure and ischemia
      • LPR threshold still debated (>25 vs >40 indicative of ischemia)
    • glucose
      • low values correlate with increased tissue injury, poor outcome
    • glutamate
      • excitatory AA neurotransmitter
      • marker of late injury
    • glycerol
      • marker of cellular stress, low oxygen or low glucose levels
      • increase with intracellular calcium entry (activates phospholipases, phosphlipid degradation, cell membrane breakdown)

 

Normative values for brain and subcutaneous microdialysis
Capture.JPG
Future uses of microdialysis

  • probes to measure higher molecular weight molecules (cytokines or inflammatory markers)
  • local drug delivery or monitor effect of systemic medications on CNS biochemistry
  • biomarker surrogate endpoint to study brain metabolism at tissue level

 

 

Reference

Frontera, Jennifer et al. “Regional Brain Monitoring In The Neurocritical Care Unit”. Neurocritical Care 22.3 (2015): 348-359.

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