title: Effects of hematocrit on cerebral microcirculation and tissue oxygenation during deep hypothermic bypass.
abstract: BACKGROUND
  One rationale for hemodilution during hypothermic cardiopulmonary bypass (CPB) has been improved microcirculation. However, the optimal degree of hemodilution remains unclear. We therefore studied cerebral microcirculation and tissue oxygenation in a new intravital microscopic model at 3 different hematocrit (Hct) values.
  
  
  RESULTS
  Three groups of 5 piglets with a cranial window over the parietal cortex underwent cooling at Hct of 10%, 20%, or 30%, followed by 1-hour deep hypothermic circulatory arrest (DHCA) and rewarming on CPB. For assessment of functional capillary density (FCD), plasma was labeled with fluorescein-isothiocyanate-dextran. Rhodamine-stained leukocytes were observed in postcapillary venules with analysis for adhesion and rolling. NADH, a natural intracellular fluorophore that increases during ischemia, was measured densitometrically during bypass and DHCA. FCD did not significantly differ from baseline during cooling in any group. However, during early reperfusion (5 minutes) after DHCA, the FCD was significantly higher in the Hct 30% group than in the Hct 10% group. Leukocyte adherence decreased in all groups during CPB and was only moderately increased at the end of the experiment. However, severe hemodilution (Hct 10%) was associated with a significantly greater number of rolling leukocytes relative to Hct 30%.
  
  
  CONCLUSIONS
  Higher Hct does not impair cerebral microcirculation and reduces white cell/endothelial activation after deep hypothermic bypass and circulatory arrest. Severe hemodilution (Hct 10%) results in evidence of inadequate cerebral tissue oxygenation during the cooling phase of CPB. This study suggests that Hct of 30% is preferable relative to lower Hct values during hypothermic CPB, particularly if DHCA is used.
authors.affiliation: Department of Cardiac Surgery, Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: L F
authors.initials: LF
authors.lastname: Duebener
authors.forename: T
authors.initials: T
authors.lastname: Sakamoto
authors.forename: S
authors.initials: S
authors.lastname: Hatsuoka
authors.forename: C
authors.initials: C
authors.lastname: Stamm
authors.forename: D
authors.initials: D
authors.lastname: Zurakowski
authors.forename: B
authors.initials: B
authors.lastname: Vollmar
authors.forename: M D
authors.initials: MD
authors.lastname: Menger
authors.forename: H J
authors.initials: HJ
authors.lastname: Schäfers
authors.forename: R A
authors.initials: RA
authors.lastname: Jonas
mesh_terms: D000818:Animals; D001831:Body Temperature / Q000502:physiology; D002315:Cardiopulmonary Bypass; D002448:Cell Adhesion / Q000502:physiology; D002452:Cell Count; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism; D006323:Heart Arrest / Q000378:metabolism; D006400:Hematocrit; D006439:Hemodynamics / Q000502:physiology; D007036:Hypothermia, Induced; D019344:Lactic Acid / Q000378:metabolism; D007958:Leukocyte Count; D007962:Leukocytes / Q000166:cytology / Q000502:physiology; D008833:Microcirculation / Q000166:cytology / Q000378:metabolism*; D008856:Microscopy, Fluorescence / Q000379:methods; D009243:NAD / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology*; D010296:Parietal Lobe / Q000098:blood supply / Q000378:metabolism; D013552:Swine
chemical_list: D009243:NAD; D019344:Lactic Acid