Cerebral microdialysis involves placement of a small catheter
with a semipermeable membrane in the parenchyma of the brain, so
that a dialysate fluid can be instilled into the catheter, allowed
to equilibrate and withdrawn for analysis (Figure 20-1). Neurochemical
levels such as lactate, pyruvate, glucose, and glutamate can then
be measured to determine metabolic and neurotransmitter activity
in the area of interest.
Diagram showing microdialysis catheter in brain parenchyma
adjacent to capillary, and molecules
of interest (ie, pyruvate, lactate, glutamate,
glucose, glycerol) entering dialysate.
- ▪ Microdialysis: A technique used to determine the chemical
composition of extracellular fluid in a tissue/organ of
- ▪ Lactate: Chemical by-product of anaerobic metabolism.
- ▪ Glutamate: Amino acid and excitatory neurotransmitter.
- ▪ Glycerol: A marker of cell membrane breakdown.
- ▪ The insertion technique for cerebral microdialysis
is similar to the technique described for ventriculostomy:
- —Shave and prepare insertion site
- —Small skin incision and burr hole
- —Incise dura and advance catheter into area of interest
- ▪ The tip of the catheter can be positioned in various
areas depending on the nature of the underlying lesion, but microdialysis
is primarily used to monitor neurochemical changes in tissue at
risk for secondary injury following a primary neurological event:
- —The catheter may be placed in the nondominant
hemisphere to monitor global cerebral events in diffuse axonal injury.
- —The catheter may be implanted in the less injured
hemisphere of a brain-injured patient to determine the effect of
whole brain interventions, such as hyperventilation on vulnerable
- —The catheter may be positioned in the penumbral
area around infarcted or contused brain to evaluate the effects
of treatments on the at-risk tissue surrounding irretrievably injured
- —The catheter may be placed in an area of tissue
perfused by arteries susceptible to vasospasm to monitor the effects
of interventions designed to treat vasospasm.
Clinical Pearls and Pitfalls
- ▪ Low glucose
levels in microdialysate indicates reduced cerebral glucose supply
and/or cerebral hypoxia and ischemia.
- ▪ An increase
in the lactate-pyruvate ratio may result from hypoxia-ischemia,
reduction in cellular redox state, mitochondrial dysfunction, or
low cerebral glucose supply and is probably the most reliable indicator
of local ischemia.
- ▪ Increased
glycerol level indicates hypoxia/ischemia and cell membrane
degradation, although it may be due to systemic events rather than
local cell breakdown.
- ▪ Increased
glutamate levels have traditionally been suspected of a causal role
in “excitotoxicity,” wherein glutamate release
after injury, but there is significant variability in glutamate
both within and among patients with brain injury.
Tisdall MM, Smith M. Cerebral microdialysis: research technique
or clinical tool. BJA.