title: Hemodilution elevates cerebral blood flow and oxygen metabolism during cardiopulmonary bypass in piglets.
abstract: BACKGROUND
  Hemodilution continues to be widely used during cardiopulmonary bypass (CPB) for both adults and children. Previous studies with nonbypass models have suggested that an increase in cerebral blood flow (CBF) compensates for the reduced oxygen-carrying capacity; however, this increased CBF is achieved by an increase in cardiac output. We hypothesized that even with the fixed-flow perfusion of CPB, CBF would be increased during hemodilution.
  
  
  METHODS
  Two experiments were conducted and analyzed separately. In each experiment, 10 piglets were randomized to two different groups, one with a total blood prime yielding a high hematocrit (25% or 30%), and the other with a crystalloid prime resulting in a low hematocrit (10% or 15%). Animals were cooled with pH-stat strategy at full flow (100 or 150 mL.kg(-1).min(-1)) to a nasopharyngeal temperature of 15 degrees C, a period of low flow (50 mL.kg(-1).min(-1)) preceding deep hypothermic circulatory arrest (45 or 60 minutes), and a period of rewarming at full flow. Cerebral blood flow was measured at the beginning of CPB, at the end of cooling, at the end of low flow, 5 minutes after the start of rewarming, and at the end of rewarming by injection of radioactive microspheres.
  
  
  RESULTS
  Mean arterial pressure was significantly greater with higher hematocrit at each time point (p< 0.05). Cerebral blood flow and the cerebral metabolic rate of oxygen decreased during cooling and further during low flow bypass but were significantly greater with lower hematocrit during mild hypothermia and at the end of rewarming (p< 0.05).
  
  
  CONCLUSIONS
  Hemodilution is associated with decreased perfusion pressure, increased CBF and increased the cerebral metabolic rate of oxygen during hypothermic CPB.
authors.affiliation: Department of Cardiovascular Surgery, Children's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: Takahiko
authors.initials: T
authors.lastname: Sakamoto
authors.forename: Georg D A
authors.initials: GD
authors.lastname: Nollert
authors.forename: David
authors.initials: D
authors.lastname: Zurakowski
authors.forename: Janet
authors.initials: J
authors.lastname: Soul
authors.forename: Lennart F
authors.initials: LF
authors.lastname: Duebener
authors.forename: Jason
authors.initials: J
authors.lastname: Sperling
authors.forename: Mitsugi
authors.initials: M
authors.lastname: Nagashima
authors.forename: George
authors.initials: G
authors.lastname: Taylor
authors.forename: Adre J
authors.initials: AJ
authors.lastname: DuPlessis
authors.forename: Richard A
authors.initials: RA
authors.lastname: Jonas
mesh_terms: D000818:Animals; D001921:Brain / Q000098:blood supply*; D002315:Cardiopulmonary Bypass; D006400:Hematocrit; D006438:Hemodilution; D007036:Hypothermia, Induced; D019344:Lactic Acid / Q000097:blood; D016014:Linear Models; D008863:Microspheres; D010100:Oxygen / Q000097:blood / Q000378:metabolism*; D011897:Random Allocation; D012039:Regional Blood Flow; D017694:Rewarming; D013552:Swine
chemical_list: D019344:Lactic Acid; D010100:Oxygen