title: Influence of PEEP on cerebral blood flow and cerebrovascular autoregulation in patients with acute respiratory distress syndrome.
abstract: BACKGROUND
  High levels of positive end-expiratory pressure (PEEP), as part of the treatment in patients with acute respiratory distress syndrome (ARDS), may prevent alveolar collapse and maintain oxygenation. PEEP potentially reduces cerebral venous return, increases intracranial blood volume, and may, therefore, affect cerebral blood flow (CBF) and cerebrovascular autoregulation (AR). This study investigates the effect of PEEP on CBF and AR in patients with respiratory failure.
  
  
  METHODS
  CBF velocity was measured using transcranial doppler and correlated with the invasive arterial blood pressure curve to calculate the index of AR Mx (Mx>0.3 indicates impaired AR). Mx was measured at lower PEEP levels and after increasing PEEP. Only an increase of Mx of >0.2 was considered to be clinically relevant. Two 1-sided Wilcoxon tests.
  
  
  RESULTS
  Twenty mechanically ventilated patients with ARDS were included. Elevation of PEEP from 9.2±1 to 14.3±1 cm H2O did not influence CBF velocity but increased Mx from 0.317±0.35 to 0.414±0.32 (difference ≤0.2). Mx was >0.3 in 11/20 patients during baseline measurements, indicating impaired AR.
  
  
  CONCLUSIONS
  Surprisingly, AR was impaired in 55% of the patients with ARDS. This should be taken into account when managing cerebral perfusion pressure to avoid cerebral hyperperfusion or hypoperfusion. Increasing PEEP from 9.2 to 14.3 cm H2O had no further clinically relevant effect on AR, independent of preexisting AR impairment.
authors.affiliation: Department of Anesthesiology, University Medical Centre, Johannes Gutenberg-University Mainz, Mainz 55131, Germany. schrammp@uni-mainz.de
authors.forename: Patrick
authors.initials: P
authors.lastname: Schramm
authors.forename: Dorothea
authors.initials: D
authors.lastname: Closhen
authors.forename: Matthias
authors.initials: M
authors.lastname: Felkel
authors.forename: Manfred
authors.initials: M
authors.lastname: Berres
authors.forename: Klaus U
authors.initials: KU
authors.lastname: Klein
authors.forename: Matthias
authors.initials: M
authors.lastname: David
authors.forename: Christian
authors.initials: C
authors.lastname: Werner
authors.forename: Kristin
authors.initials: K
authors.lastname: Engelhard
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001794:Blood Pressure / Q000502:physiology; D001810:Blood Volume / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003422:Critical Care; D005260:Female; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D006993:Hypnotics and Sedatives; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption; D011175:Positive-Pressure Respiration; D011300:Preoperative Care; D012128:Respiratory Distress Syndrome / Q000503:physiopathology* / Q000628:therapy; D017585:Ultrasonography, Doppler, Transcranial
chemical_list: D006993:Hypnotics and Sedatives; D010100:Oxygen