title: Hemodilution Combined With Hypercapnia Impairs Cerebral Autoregulation During Normothermic Cardiopulmonary Bypass.
abstract: OBJECTIVE
  To investigate the influence of hemodilution and arterial pCO2 on cerebral autoregulation and cerebral vascular CO2 reactivity.
  
  
  METHODS
  Prospective interventional study.
  
  
  METHODS
  University hospital-based single-center study.
  
  
  METHODS
  Forty adult patients undergoing elective cardiac surgery using normothermic cardiopulmonary bypass.
  
  
  METHODS
  Blood pressure variations induced by 6/minute metronome-triggered breathing (baseline) and cyclic 6/min changes of indexed pump flow at 3 levels of arterial pCO2.
  
  
  RESULTS
  Based on median hematocrit on bypass, patients were assigned to either a group of a hematocrit ≥28% or<28%. The autoregulation index was calculated from cerebral blood flow velocity and mean arterial blood pressure using transfer function analysis. Cerebral vascular CO2 reactivity was calculated using cerebral tissue oximetry data. Cerebral autoregulation as reflected by autoregulation index (baseline 7.5) was significantly affected by arterial pCO2 (median autoregulation index amounted to 5.7, 4.8, and 2.8 for arterial pCO2 of 4.0, 5.3, and 6.6 kPa, p≤0.002) respectively. Hemodilution resulted in a decreased autoregulation index; however, during hypocapnia and normocapnia, there were no significant differences between the two hematocrit groups. Moreover, the autoregulation index was lowest during hypercapnia when hematocrit was<28% (autoregulation index 3.3 versus 2.6 for hematocrit ≥28% and<28%, respectively, p = 0.014). Cerebral vascular CO2 reactivity during hypocapnia was significantly lower when perioperative hematocrit was<28% (p = 0.018).
  
  
  CONCLUSIONS
  Hemodilution down to a hematocrit of<28% combined with hypercapnia negatively affects dynamic cerebral autoregulation, which underlines the importance of tight control of both hematocrit and paCO2 during CPB.
authors.affiliation: Departments of Cardiothoracic Surgery.
authors.forename: Ervin E
authors.initials: EE
authors.lastname: Ševerdija
authors.affiliation: Departments of Cardiothoracic Surgery. Electronic address: nousjka.vranken@mumc.nl.
authors.forename: Nousjka P A
authors.initials: NP
authors.lastname: Vranken
authors.affiliation: Departments of Cardiothoracic Surgery.
authors.forename: Antoine P
authors.initials: AP
authors.lastname: Simons
authors.affiliation: Clinical Neurophysiology.
authors.forename: Erik D
authors.initials: ED
authors.lastname: Gommer
authors.affiliation: Anesthesiology, Maastricht University Medical Center, AZ Maastricht, The Netherlands.
authors.forename: John H
authors.initials: JH
authors.lastname: Heijmans
authors.affiliation: Departments of Cardiothoracic Surgery.
authors.forename: Jos G
authors.initials: JG
authors.lastname: Maessen
authors.affiliation: Departments of Cardiothoracic Surgery.
authors.forename: Patrick W
authors.initials: PW
authors.lastname: Weerwind
mesh_terms: D002245:Carbon Dioxide / Q000097:blood; D002315:Cardiopulmonary Bypass; D002560:Cerebrovascular Circulation / Q000502:physiology*; D006438:Hemodilution / Q000009:adverse effects*; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D011446:Prospective Studies
chemical_list: D002245:Carbon Dioxide
keywords: cardiopulmonary bypass; cerebral autoregulation; cerebral carbon dioxide reactivity; hemodilution