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Brain Tissue Oxygenation and Cerebral Perfusion Pressure Thresholds of Ischemia in a Standardized Pig Brain Death Model
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Neurosurgery.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Neurosurgery.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Surgical Sciences, Anaesthesiology and Intensive Care.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Neurosurgery.
2012 (English)In: Neurocritical Care, ISSN 1541-6933, E-ISSN 1556-0961, Vol. 16, no 3, 462-469 p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND:

Neurointensive care of traumatic brain injury (TBI) patients is currently based on intracranial pressure (ICP) and cerebral perfusion pressure (CPP) targeted protocols. Monitoring brain tissue oxygenation (B(ti)pO(2)) is of considerable clinical interest, but the exact threshold level of ischemia has been difficult to establish due to the complexity of the clinical situation. The objective of this study was to use the Neurovent-PTO (NV) probe, and to define critical cerebral oxygenation- and CPP threshold levels of cerebral ischemia in a standardized brain death model caused by increasing the ICP in pig. Ischemia was defined by a severe increase of cerebral microdialysis (MD) lactate/pyruvate ratio (L/P ratio > 30).

METHODS:

B(ti)pO(2), L/P ratio, Glucose, Glutamate, Glycerol and CPP were recorded using NV and MD probes during gradual increase of ICP by inflation of an epidural balloon catheter with saline until brain death was achieved.

RESULTS:

Baseline level of B(ti)pO(2) was 22.9 ± 6.2 mmHg, the L/P ratio 17.7 ± 6.1 and CPP 73 ± 17 mmHg. B(ti)pO(2) and CPP decreased when intracranial volume was added. The L/P ratio increased above its ischemic levels, (>30) when CPP decreased below 30 mmHg and B(ti)pO(2) to <10 mmHg.

CONCLUSIONS:

A severe increase of ICP leading to CPP below 30 mmHg and B(ti)pO(2) below 10 mmHg is associated with an increase of the L/P ratio, thus seems to be critical thresholds for cerebral ischemia under these conditions.

Place, publisher, year, edition, pages
2012. Vol. 16, no 3, 462-469 p.
Keyword [en]
Brain tissue oxygenation, Cerebral perfusion pressure, Microdialysis, Threshold levels, Traumatic brain injury
National Category
Neurosciences
Research subject
Neurosurgery; Neuroscience
Identifiers
URN: urn:nbn:se:uu:diva-170951DOI: 10.1007/s12028-012-9675-3ISI: 000304619000019OAI: oai:DiVA.org:uu-170951DiVA: diva2:509930
Available from: 2012-03-16 Created: 2012-03-14 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Brain Tissue Oxygenation in Traumatic Brain Injury: Experimental and Clinical Studies
Open this publication in new window or tab >>Brain Tissue Oxygenation in Traumatic Brain Injury: Experimental and Clinical Studies
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Traumatic brain injury (TBI) is a major cause of death and disability. TBI is frequently followed by cerebral ischemia which is a great contributor to secondary brain damage. The main causes of cerebral ischemia are pathophysiological changes in cerebral blood flow and metabolism. Treatment of TBI patients is currently based on intracranial pressure (ICP) and cerebral perfusion pressure (CPP) targeted treatment protocols. However, ICP and CPP alone do not provide information of the oxygen availability in the brain. Monitoring of brain tissue oxygenation (BtipO2) may give additional and valuable information about the risk for development of ischemia in TBI patients.

The aims of this thesis were to study BtipO2 monitoring devices in-vitro regarding accuracy and stability, to detect threshold level of cerebral ischemia in-vivo and finally to examine the cerebral oxygen levels and cerebral metabolism in TBI patients.

The BtipO2 probes performed with high accuracy and stability at different clinically relevant oxygen concentrations.

A pig TBI model was developed by step-wise intracranial volume/pressure increase. Volume increase resulted in a gradual increased ICP, decreased CPP, intracranial compliance and BtipO2, respectively. Brain death (BD) was confirmed by negative CPP and negligible amount of previously injected microspheres in the brain tissue. The model simulated the clinical development of BD in humans with a classical pressure-volume response and systemic cardiovascular reactions. The model should be suitable for studies of brain injury mechanisms.

From the same in-vivo model it was also possible to detect the threshold level of cerebral ischemia in the pig, where BtipO2 below 10 mmHg and CPP below 30 mmHg was associated with an impaired cerebral metabolism (microdialysis lactate to pyruvate ratio >30).

BtipO2 together with cerebral microdialysis were studied in 23 severe TBI patients. We observed different patterns of changes in BtipO2 and cerebral microdialysis biomarkers in focal and diffuse TBI.  Increased cerebral microdialysis levels of glutamate, glycerol or the lactate/pyruvate ratio were observed at BtipO2 < 5 mmHg, indicating increased vulnerability of the brain at this critical level of tissue oxygenation in TBI patients.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 74 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 869
Keyword
Brain tissue oxygenation, Cerebral metabolism, Traumatic brain injury, Cerebral ischemia, Threshold levels, Neurovent-PTO, Microdialysis
National Category
Medical and Health Sciences Anesthesiology and Intensive Care Neurosciences
Research subject
Neurosurgery
Identifiers
urn:nbn:se:uu:diva-195867 (URN)978-91-554-8607-5 (ISBN)
Public defence
2013-04-19, Grönwallsalen, Akademiska sjukhuset, ingång 70, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2013-03-27 Created: 2013-02-28 Last updated: 2013-04-02Bibliographically approved

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Purins, KarlisEnblad, PerWiklund, LarsLewén, Anders

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