title: Effects of positive end-expiratory pressure on regional cerebral blood flow, intracranial pressure, and brain tissue oxygenation.
abstract: OBJECTIVE
  Acute respiratory dysfunction frequently occurs following severe aneurysmal subarachnoid hemorrhage requiring positive end-expiratory pressure (PEEP) ventilation to maintain adequate oxygenation. High PEEP levels, however, may negatively affect cerebral perfusion. The goal of this study was, to examine the influence of various PEEP levels on intracranial pressure, brain tissue oxygen tension, regional cerebral blood flow, and systemic hemodynamic variables.
  
  
  METHODS
  Animal research and clinical intervention study.
  
  
  METHODS
  Surgical intensive care unit of a university hospital.
  
  
  METHODS
  Experiments were carried out in five healthy pigs, followed by a clinical investigation of ten patients suffering subarachnoid hemorrhage.
  
  
  METHODS
  Under continuous monitoring of intracranial pressure, brain tissue oxygen tension, regional cerebral blood flow, mean arterial pressure, and cardiac output, PEEP was applied in increments of 5 cm H2O from 5 to 25 cm H2O in the experimental part and from baseline to 20 cm H2O in the clinical part.
  
  
  RESULTS
  In animals, high PEEP levels had no adverse effect on intracranial pressure, brain tissue oxygen tension, or regional cerebral blood flow. In patients with severe subarachnoid hemorrhage, stepwise elevation of PEEP resulted in a significant decrease of mean arterial pressure and regional cerebral blood flow. Analyses of covariance revealed that these changes of regional cerebral blood flow depended on mean arterial pressure changes as a result of a disturbed cerebrovascular autoregulation. Consequently, normalization of mean arterial pressure restored regional cerebral blood flow to baseline values.
  
  
  CONCLUSIONS
  Application of high PEEP does not impair intracranial pressure or regional cerebral blood flow per se but may indirectly affect cerebral perfusion via its negative effect on macrohemodynamic variables in case of a disturbed cerebrovascular autoregulation. Therefore, following severe subarachnoid hemorrhage, a PEEP-induced decrease of mean arterial pressure should be reversed to maintain cerebral perfusion.
authors.affiliation: Departments of Anesthesiology, Klinikum Mannheim, University of Heidelberg, Mannheim, Germany.
authors.forename: Elke
authors.initials: E
authors.lastname: Muench
authors.forename: Christian
authors.initials: C
authors.lastname: Bauhuf
authors.forename: Harry
authors.initials: H
authors.lastname: Roth
authors.forename: Peter
authors.initials: P
authors.lastname: Horn
authors.forename: Marc
authors.initials: M
authors.lastname: Phillips
authors.forename: Natali
authors.initials: N
authors.lastname: Marquetant
authors.forename: Michael
authors.initials: M
authors.lastname: Quintel
authors.forename: Peter
authors.initials: P
authors.lastname: Vajkoczy
mesh_terms: D000328:Adult; D000368:Aged; D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D001921:Brain / Q000378:metabolism* / Q000503:physiopathology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D007427:Intracranial Pressure / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology*; D011175:Positive-Pressure Respiration; D013345:Subarachnoid Hemorrhage / Q000378:metabolism / Q000503:physiopathology* / Q000628:therapy; D013552:Swine