title: Pressure autoregulation, intracranial pressure, and brain tissue oxygenation in children with severe traumatic brain injury.
abstract: OBJECTIVE
  Cerebral pressure autoregulation is an important neuroprotective mechanism that stabilizes cerebral blood flow when blood pressure (BP) changes. In this study the authors examined the association between autoregulation and clinical factors, BP, intracranial pressure (ICP), brain tissue oxygen tension (PbtO(2)), and outcome after pediatric severe traumatic brain injury (TBI). In particular we examined how the status of autoregulation influenced the effect of BP changes on ICP and PbtO(2).
  
  
  METHODS
  In this prospective observational study, 52 autoregulation tests were performed in 24 patients with severe TBI. The patients had a mean age of 6.3 +/- 3.2 years, and a postresuscitation Glasgow Coma Scale score of 6 (range 3-8). All patients underwent continuous ICP and PbtO(2) monitoring, and transcranial Doppler ultrasonography was used to examine the autoregulatory index (ARI) based on blood flow velocity of the middle cerebral artery after increasing mean arterial pressure by 20% of the baseline value. Impaired autoregulation was defined as an ARI < 0.4 and intact autoregulation as an ARI >or= 0.4. The relationships between autoregulation (measured as both a continuous and dichotomous variable), outcome, and clinical and physiological variables were examined using multiple logistic regression analysis.
  
  
  RESULTS
  Autoregulation was impaired (ARI < 0.4) in 29% of patients (7 patients). The initial Glasgow Coma Scale score was significantly associated with the ARI (p = 0.02, r = 0.32) but no other clinical factors were associated with autoregulation status. Baseline values at the time of testing for ICP, PbtO(2), the ratio of PbtO(2)/PaO(2), mean arterial pressure, and middle cerebral artery blood flow velocity were similar in the patients with impaired or intact autoregulation. There was an inverse relationship between ARI (continuous and dichotomous) with a change in ICP (continuous ARI, p = 0.005; dichotomous ARI, p = 0.02); that is, ICP increased with the BP increase when ARI was low (weak autoregulation). The ARI (continuous and dichotomous) was also inversely associated with a change in PbtO(2) (continuous ARI, p = 0.002; dichotomous ARI, p = 0.02). The PbtO(2) increased when BP was increased in most patients, even when the ARI was relatively high (stronger autoregulation), but the magnitude of this response was still associated with the ARI. There was no relationship between the ARI and outcome.
  
  
  CONCLUSIONS
  These data demonstrate the influence of the strength of autoregulation on the response of ICP and PbtO(2) to BP changes and the variability of this response between individuals. The findings suggest that autoregulation testing may assist clinical decision-making in pediatric severe TBI and help better define optimal BP or cerebral perfusion pressure targets for individual patients.
authors.affiliation: Division of Neurosurgery, School of Child and Adolescent Health, University of Cape Town, Red Cross Children's Hospital, Cape Town, South Africa. Anthony.Figaji@uct.ac.za
authors.forename: Anthony A
authors.initials: AA
authors.lastname: Figaji
authors.forename: Eugene
authors.initials: E
authors.lastname: Zwane
authors.forename: A Graham
authors.initials: AG
authors.lastname: Fieggen
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Argent
authors.forename: Peter D
authors.initials: PD
authors.lastname: Le Roux
authors.forename: Peter
authors.initials: P
authors.lastname: Siesjo
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Peter
mesh_terms: D001794:Blood Pressure / Q000502:physiology*; D001930:Brain Injuries / Q000378:metabolism / Q000503:physiopathology*; D002648:Child; D002675:Child, Preschool; D005260:Female; D015600:Glasgow Coma Scale; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D007223:Infant; D007427:Intracranial Pressure / Q000502:physiology*; D016014:Linear Models; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology*; D011446:Prospective Studies; D011680:Pupil / Q000502:physiology; D016896:Treatment Outcome; D017585:Ultrasonography, Doppler, Transcranial