title: Short pressure reactivity index versus long pressure reactivity index in the management of traumatic brain injury.
abstract: OBJECTIVE
  The pressure reactivity index (PRx) correlates with outcome after traumatic brain injury (TBI) and is used to calculate optimal cerebral perfusion pressure (CPPopt). The PRx is a correlation coefficient between slow, spontaneous changes (0.003-0.05 Hz) in intracranial pressure (ICP) and arterial blood pressure (ABP). A novel index-the so-called long PRx (L-PRx)-that considers ABP and ICP changes (0.0008-0.008 Hz) was proposed.
  
  
  METHODS
  The authors compared PRx and L-PRx for 6-month outcome prediction and CPPopt calculation in 307 patients with TBI. The PRx- and L-PRx-based CPPopt were determined and the predictive power and discriminant abilities were compared.
  
  
  RESULTS
  The PRx and L-PRx correlation was good (R = 0.7, p < 0.00001; Spearman test). The PRx, age, CPP, and Glasgow Coma Scale score but not L-PRx were significant fatal outcome predictors (death and persistent vegetative state). There was a significant difference between the areas under the receiver operating characteristic curves calculated for PRx and L-PRx (0.61 ± 0.04 vs 0.51 ± 0.04; z-statistic = -3.26, p = 0.011), which indicates a better ability by PRx than L-PRx to predict fatal outcome. The CPPopt was higher for L-PRx than for PRx, without a statistical difference (median CPPopt for L-PRx: 76.9 mm Hg, interquartile range [IQR] ± 10.1 mm Hg; median CPPopt for PRx: 74.7 mm Hg, IQR ± 8.2 mm Hg). Death was associated with CPP below CPPopt for PRx (χ(2) = 30.6, p < 0.00001), and severe disability was associated with CPP above CPPopt for PRx (χ(2) = 7.8, p = 0.005). These relationships were not statistically significant for CPPopt for L-PRx.
  
  
  CONCLUSIONS
  The PRx is superior to the L-PRx for TBI outcome prediction. Individual CPPopt for L-PRx and PRx are not statistically different. Deviations between CPP and CPPopt for PRx are relevant for outcome prediction; those between CPP and CPPopt for L-PRx are not. The PRx uses the entire B-wave spectrum for index calculation, whereas the L-PRX covers only one-third of it. This may explain the performance discrepancy.
authors.affiliation: Neurosurgical Associates, Red Cross Hospital, Kassel;
authors.forename: Erhard W
authors.initials: EW
authors.lastname: Lang
authors.forename: Magdalena
authors.initials: M
authors.lastname: Kasprowicz
authors.forename: Peter
authors.initials: P
authors.lastname: Smielewski
authors.forename: Edgar
authors.initials: E
authors.lastname: Santos
authors.forename: John
authors.initials: J
authors.lastname: Pickard
authors.forename: Marek
authors.initials: M
authors.lastname: Czosnyka
mesh_terms: D000328:Adult; D000368:Aged; D001930:Brain Injuries / Q000401:mortality / Q000503:physiopathology / Q000628:therapy*; D015170:Cerebrospinal Fluid Pressure / Q000502:physiology*; D005260:Female; D015600:Glasgow Coma Scale; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012015:Reference Standards; D012189:Retrospective Studies; D012307:Risk Factors; D015599:Trauma Severity Indices; D016896:Treatment Outcome
keywords: ABP = arterial blood pressure; CPPopt = optimal cerebral perfusion pressure; GCS = Glasgow Coma Scale; GOS = Glasgow Outcome Scale; ICP = intracranial pressure; IQR = interquartile range; L-PRx = long pressure reactivity index; PVS = persistent vegetative state; TBI = traumatic brain injury; brain monitoring; cerebral autoregulation; cerebral perfusion pressure; cerebrovascular reactivity; outcome; severe head injury; traumatic brain injury