title: Correlation between cerebral blood flow, substrate delivery, and metabolism in head injury: a combined microdialysis and triple oxygen positron emission tomography study.
abstract: Microdialysis continuously monitors the chemistry of a small focal volume of the cerebral extracellular space. Conversely, positron emission tomography (PET) establishes metabolism of the whole brain, but only for the duration of the scan. The objective of this study was to apply both techniques to head-injured patients simultaneously to assess the relation between microdialysis (glucose, lactate, lactate/pyruvate [L/P] ratio, and glutamate) and PET (cerebral blood flow [CBF], cerebral blood volume, oxygen extraction fraction (OEF), and cerebral metabolic rate of oxygen) parameters. Microdialysis catheters were inserted into the frontal cerebral cortex and adipose tissue of the anterior abdominal wall of 17 severely head-injured patients. Microdialysis was performed during PET scans, with regions of interest defined by the location of the microdialysis catheter membrane. An intervention (hyperventilation) was performed in 13 patients. The results showed that combining PET and microdialysis to monitor metabolism in ventilated patients is feasible and safe, although logistically complex. There was a significant relation between the L/P ratio and the OEF (Spearman r = 0.69, P = 0.002). There was no significant relation between CBF and the microdialysis parameters. Moderate short-term hyperventilation appeared to be tolerated in terms of brain chemistry, although no areas were sampled by microdialysis where the OEF exceeded 70%. Hyperventilation causing a reduction of the arterial carbon dioxide tension by 0.9 kPa resulted in a significant elevation of the OEF, in association with a reduction in glucose, but no significant elevation in the L/P ratio or glutamate.
authors.affiliation: Department of Neurosurgery, Addenbrooke's Hospital, University of Cambridge, Cambridge, UK. p.hutch@which.net
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Hutchinson
authors.forename: Arun K
authors.initials: AK
authors.lastname: Gupta
authors.forename: Tim F
authors.initials: TF
authors.lastname: Fryer
authors.forename: Pippa G
authors.initials: PG
authors.lastname: Al-Rawi
authors.forename: Doris A
authors.initials: DA
authors.lastname: Chatfield
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Coles
authors.forename: Mark T
authors.initials: MT
authors.lastname: O'Connell
authors.forename: Rupert
authors.initials: R
authors.lastname: Kett-White
authors.forename: Pawan S
authors.initials: PS
authors.lastname: Minhas
authors.forename: Franklin I
authors.initials: FI
authors.lastname: Aigbirhio
authors.forename: John C
authors.initials: JC
authors.lastname: Clark
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Kirkpatrick
authors.forename: David K
authors.initials: DK
authors.lastname: Menon
authors.forename: John D
authors.initials: JD
authors.lastname: Pickard
mesh_terms: D000293:Adolescent; D000328:Adult; D001921:Brain / Q000098:blood supply / Q000378:metabolism*; D001923:Brain Chemistry / Q000502:physiology; D001930:Brain Injuries / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000503:physiopathology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D005947:Glucose / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism; D006801:Humans; D006985:Hyperventilation / Q000000981:diagnostic imaging / Q000378:metabolism / Q000503:physiopathology; D019344:Lactic Acid / Q000378:metabolism; D008297:Male; D017551:Microdialysis; D008875:Middle Aged; D019289:Pyruvic Acid / Q000378:metabolism; D014055:Tomography, Emission-Computed
chemical_list: D019344:Lactic Acid; D018698:Glutamic Acid; D019289:Pyruvic Acid; D005947:Glucose