title: Brain tissue oxygen tension is more indicative of oxygen diffusion than oxygen delivery and metabolism in patients with traumatic brain injury.
abstract: OBJECTIVE
  Despite the growing clinical use of brain tissue oxygen monitoring, the specific determinants of low brain tissue oxygen tension (P(bt)O2) following severe traumatic brain injury (TBI) remain poorly defined. The objective of this study was to evaluate whether P(bt)O2 more closely reflects variables related to cerebral oxygen diffusion or reflects cerebral oxygen delivery and metabolism.
  
  
  METHODS
  Prospective observational study.
  
  
  METHODS
  Level I trauma center.
  
  
  METHODS
  Fourteen TBI patients with advanced neuromonitoring underwent an oxygen challenge (increase in FiO2 to 1.0) to assess tissue oxygen reactivity, pressure challenge (increase in mean arterial pressure) to assess autoregulation, and CO2 challenge (hyperventilation) to assess cerebral vasoreactivity.
  
  
  METHODS
  None.
  
  
  RESULTS
  P(bt)O2 was measured directly with a parenchymal probe in the least-injured hemisphere. Local cerebral blood flow (CBF) was measured with a parenchymal thermal diffusion probe. Cerebral venous blood gases were drawn from a jugular bulb venous catheter. We performed 119 measurements of PaO2, arterial oxygen content (CaO2), jugular bulb venous oxygen tension (PVO2), venous oxygen content (CVO2), arteriovenous oxygen content difference (AVDO2), and local cerebral metabolic rate of oxygen (locCMRO2). In multivariable analysis adjusting for various variables of cerebral oxygen delivery and metabolism, the only statistically significant relationship was that between P(bt)O2 and the product of CBF and cerebral arteriovenous oxygen tension difference (AVTO2), suggesting a strong association between brain tissue oxygen tension and diffusion of dissolved plasma oxygen across the blood-brain barrier.
  
  
  CONCLUSIONS
  Measurements of P(bt)O2 represent the product of CBF and the cerebral AVTO2 rather than a direct measurement of total oxygen delivery or cerebral oxygen metabolism. This improved understanding of the cerebral physiology of P(bt)O2 should enhance the clinical utility of brain tissue oxygen monitoring in patients with TBI.
authors.affiliation: Department of Neurosurgery, University of California, San Francisco, USA.
authors.forename: Guy
authors.initials: G
authors.lastname: Rosenthal
authors.forename: J Claude
authors.initials: JC
authors.lastname: Hemphill
authors.forename: Marco
authors.initials: M
authors.lastname: Sorani
authors.forename: Christine
authors.initials: C
authors.lastname: Martin
authors.forename: Diane
authors.initials: D
authors.lastname: Morabito
authors.forename: Walter D
authors.initials: WD
authors.lastname: Obrist
authors.forename: Geoffrey T
authors.initials: GT
authors.lastname: Manley
mesh_terms: D000293:Adolescent; D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D001921:Brain / Q000098:blood supply*; D001930:Brain Injuries / Q000503:physiopathology / Q000628:therapy*; D002245:Carbon Dioxide / Q000097:blood; D003422:Critical Care; D004058:Diffusion; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D015600:Glasgow Coma Scale; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D007427:Intracranial Pressure; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption / Q000502:physiology*; D010102:Oxygen Inhalation Therapy; D011446:Prospective Studies; D012039:Regional Blood Flow / Q000502:physiology; D014193:Trauma Centers
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen