title: Increased risk of critical CBF levels in SAH patients with actual CPP below calculated optimal CPP.
abstract: Cerebral pressure autoregulation can be quantified with the pressure reactivity index (PRx), based on the correlation between blood pressure and intracranial pressure. Using PRx optimal cerebral perfusion pressure (CPPopt) can be calculated, i.e., the level of CPP where autoregulation functions best. The relation between cerebral blood flow (CBF) and CPPopt has not been examined. The objective was to assess to which extent CPPopt can be calculated in SAH patients and to investigate CPPopt in relation to CBF.
  
  
  
  Retrospective study of prospectively collected data. CBF was measured bedside with Xenon-enhanced CT (Xe-CT). The difference between actual CPP and CPPopt was calculated (CPP∆). Correlations between CPP∆ and CBF parameters were calculated with Spearman's rank order correlation coefficient (rho). Separate calculations were done using all patients (day 0-14 after onset) as well as in two subgroups (day 0-3 and day 4-14).
  
  
  
  Eighty-two patients with 145 Xe-CT scans were studied. Automated calculation of CPPopt was possible in adjunct to 60% of the Xe-CT scans. Actual CPP < CPPopt was associated with higher numbers of low-flow regions (CBF <10 ml/100 g/min) in both the early phase (day 0-3, n = 39, Spearman's rho = -0.38, p = 0.02) and late acute phase of the disease (day 4-14, n = 35, Spearman's rho = -0.39, p = 0.02). CPP level per se was not associated with CBF.
  
  
  
  Calculation of CPPopt is possible in a majority of patients with severe SAH. Actual CPP below CPPopt is associated with low CBF.
authors.affiliation: Department of Neuroscience/Neurosurgery, Uppsala University, S-75185, Uppsala, Sweden. Ulf.johnson@neuro.uu.se.|Department of Surgical sciences/Radiology, Uppsala University, Uppsala, Sweden. Ulf.johnson@neuro.uu.se.
authors.forename: Ulf
authors.initials: U
authors.lastname: Johnson
authors.affiliation: Department of Neuroscience/Neurosurgery, Uppsala University, S-75185, Uppsala, Sweden.|Department of Surgical sciences/Anaesthesia and Intensive care, Uppsala University, Uppsala, Sweden.
authors.forename: Henrik
authors.initials: H
authors.lastname: Engquist
authors.affiliation: Department of Neuroscience/Neurosurgery, Uppsala University, S-75185, Uppsala, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Lewén
authors.affiliation: Department of Neuroscience/Neurosurgery, Uppsala University, S-75185, Uppsala, Sweden.
authors.forename: Tim
authors.initials: T
authors.lastname: Howells
authors.affiliation: Department of Neuroscience/Neurosurgery, Uppsala University, S-75185, Uppsala, Sweden.
authors.forename: Pelle
authors.initials: P
authors.lastname: Nilsson
authors.affiliation: Department of Neuroscience/Neurosurgery, Uppsala University, S-75185, Uppsala, Sweden.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Ronne-Engström
authors.affiliation: Department of Neuroscience/Neurosurgery, Uppsala University, S-75185, Uppsala, Sweden.
authors.forename: Elham
authors.initials: E
authors.lastname: Rostami
authors.affiliation: Department of Neuroscience/Neurosurgery, Uppsala University, S-75185, Uppsala, Sweden.
authors.forename: Per
authors.initials: P
authors.lastname: Enblad
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002560:Cerebrovascular Circulation; D005260:Female; D006801:Humans; D007427:Intracranial Pressure; D008297:Male; D008875:Middle Aged; D013345:Subarachnoid Hemorrhage / Q000175:diagnosis* / Q000000981:diagnostic imaging
keywords: Autoregulation; CBF; CPPopt; Cerebral blood flow; Cerebral perfusion pressure; Neurointensive care; Optimal; SAH; Subarachnoid hemorrhage