title: 'Long' pressure reactivity index (L-PRx) as a measure of autoregulation correlates with outcome in traumatic brain injury patients.
abstract: BACKGROUND
  Cerebral autoregulation and, consequently, cerebrovascular pressure reactivity, can be disturbed after traumatic brain injury (TBI). Continuous monitoring of autoregulation has shown its clinical importance as an independent predictor of neurological outcome. The cerebral pressure reactivity index (PRx) reflects that changes in seconds of cerebrovascular reactivity have prognostic significance. Using an alternative algorithm similar to PRx, we investigate whether the utilization of lower-frequency changes of the order of minutes of mean arterial blood pressure (MAP) and intracranial pressure (ICP) could have a prognostic value in TBI patients.
  
  
  METHODS
  Head-injured patients requiring continued advanced multimodal monitoring, including hemodynamic, ICP and microdialysis (MD) monitoring, were analyzed retrospectively. A low-frequency sample pressure reactivity index (L-PRx) was calculated, using 20-min averages of MAP and ICP data as a linear Pearson's correlation. The mean values per patient were correlated to outcome at 6 months after injury. Differences of monitoring parameters between non-survivors and survivors were compared.
  
  
  RESULTS
  A total of 29 patients (mean age 37.2 years, 26 males) suffering from TBI were monitored for a mean of 109.6 h (16-236 h, SD ± 60.4). Mean L-PRx was found to be of 0.1 (-0.2 to 0.6, SD ± 0.20), six patients presented impaired (>0.2) values. The averaged L-PRx correlated significantly with ICP (r = 0.467, p = 0.011) and 6-month outcome (r = -0.556, p = 0.002). Significant statistical differences were found in L-PRx, cerebral perfusion pressure (CPP), lactate, and lactate-pyruvate ratio when comparing patients who died (n = 5) and patients who survived.
  
  
  CONCLUSIONS
  L-PRx correlates with the 6-month outcome in TBI patients. Very slow changes of MAP and ICP may contain important autoregulation information. L-PRx may be an alternative algorithm for the estimation of cerebral autoregulation and clinical prognosis.
authors: Department of Neurosurgery, University Hospital Heidelberg, Heidelberg, Germany, Renan.Sanchez-Porras@med.uni-heidelberg.de
authors: Renán
authors: R
authors: Sánchez-Porras
authors: Edgar
authors: E
authors: Santos
authors: Marek
authors: M
authors: Czosnyka
authors: Zelong
authors: Z
authors: Zheng
authors: Andreas W
authors: AW
authors: Unterberg
authors: Oliver W
authors: OW
authors: Sakowitz
mesh_terms: D000328:Adult; D000465:Algorithms; D062186:Arterial Pressure / Q000502:physiology*; D001786:Blood Glucose / Q000378:metabolism; D001921:Brain / Q000098:blood supply; D001930:Brain Injuries / Q000401:mortality / Q000503:physiopathology*; D004185:Disability Evaluation; D005260:Female; D018698:Glutamic Acid / Q000097:blood; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D007427:Intracranial Pressure / Q000502:physiology*; D019344:Lactic Acid / Q000097:blood; D008297:Male; D011379:Prognosis; D019289:Pyruvic Acid / Q000097:blood; D012189:Retrospective Studies; D015996:Survival Rate
chemical_list: D001786:Blood Glucose; D019344:Lactic Acid; D018698:Glutamic Acid; D019289:Pyruvic Acid