title: Cerebral response to hemodilution during hypothermic cardiopulmonary bypass in adults.
abstract: We examined the cerebral response to changing hematocrit during hypothermic cardiopulmonary bypass (CPB) in 18 adults. Cerebral blood flow (CBF), cerebral metabolic rate for oxygen (CMRO2), and cerebral oxygen delivery (CDO2) were determined using the nitrous oxide saturation technique. Measurements were obtained before CPB at 36 degrees C, and twice during 27 degrees C CPB: first with a hemoglobin (Hgb) of 6.2 +/- 1.2 g/dL and then with a Hgb of 8.5 +/- 1.2 g/dL. During hypothermia, appropriate reductions in CMRO2 were demonstrated, but hemodilution-associated increases in CBF offset the reduction in CBF seen with hypothermia. At 27 degrees C CPB, as the Hgb concentration was increased from 6.2 to 8.5 g/ dL, CBF decreased. CDO2 and CMRO2 were no different whether the Hgb was 6.2 or 8.5 g/dL. In eight patients in whom the Hgb was less than 6 g/dL, CDO2 remained more than twice CMRO2.
  
  
  CONCLUSIONS
  This study suggests that cerebral oxygen balance during cardiopulmonary bypass is well maintained at more pronounced levels of hemodilution than are typically practiced, because changes in cerebral blood flow compensate for changes in hemoglobin concentration.
authors.affiliation: Pamukkale University Medical School, Denizli, Turkey.
authors.forename: H
authors.initials: H
authors.lastname: Sungurtekin
authors.forename: D J
authors.initials: DJ
authors.lastname: Cook
authors.forename: T A
authors.initials: TA
authors.lastname: Orszulak
authors.forename: R C
authors.initials: RC
authors.lastname: Daly
authors.forename: C J
authors.initials: CJ
authors.lastname: Mullany
mesh_terms: D000368:Aged; D001921:Brain / Q000378:metabolism*; D006348:Cardiac Surgical Procedures; D002315:Cardiopulmonary Bypass; D002560:Cerebrovascular Circulation; D006438:Hemodilution; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D007036:Hypothermia, Induced; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption
chemical_list: D006454:Hemoglobins; D010100:Oxygen