title: Effects of pH management during deep hypothermic bypass on cerebral oxygenation: alpha-stat versus pH-stat.
abstract: OBJECTIVE
  There is a remarkable lack of scientific evidence to support the option to use alpha-stat or pH-stat management, as to which is more beneficial to brain protection during deep hypothermic CPB. This study examined cortical blood flow (CBF), cerebral oxygenation, and brain oxygen consumption in relation to deep hypothermic CPB with alpha-stat or pH-stat management.
  
  
  METHODS
  Twenty-two pigs were cooled with alpha-stat or pH-stat during CPB to 15 degrees C esophageal temperature. CBF and cerebral oxygenation were measured continuously with a laser flowmeter and near-infrared spectroscopy, respectively. Brain oxygen consumption was measured with standard laboratory techniques.
  
  
  RESULTS
  During CPB cooling, CBF was significantly decreased, about 52.2%+/-6.3% (P<0.01 vs 92.6%+/-6.5% of pH-stat) at 15 degrees C in alpha-stat, whereas there were no significant changes in CBF in pH-stat. While cooling down, brain oxygen extraction (OER) progressively decreased, about 9.5%+/-0.9% and 10.9%+/-1.5% at 15 degrees C in alpha-stat and pH-stat, respectively. At 31 degrees C the decreased value in pH-stat was lower than in alpha-stat (29.9%+/-2.7% vs 22.5%+/-1.9%; P<0.05). The ratio of CBF/OER were 2.0+/-0.3 in alpha-stat and pH-stat, respectively; it was kept in constant level in alpha-stat, and significantly increased by 19 degrees C to 15 degrees C in pH-stat (4.9+/-0.9 vs 2.3+/-0.4; P<0.01). In mild hypothermia, cerebral oxyhemoglobin and oxygen saturation in alpha-stat were greater than that in pH-stat (102.5%+/-1.4% vs 99.1%+/-0.7%; P<0.05). In deep hypothermia, brain oxygen saturation in pH-stat was greater than that in alpha-stat (99.2%+/-1.0% vs 93.8%+/-1.0%; P<0.01), and deoxyhemoglobin in pH-stat decreased more greatly than that in alpha-stat (28.7%+/-6.8% vs 54.1%+/-4.7%; P<0.05).
  
  
  CONCLUSIONS
  In mild hypothermic CPB, brain tissue oxygen saturation was greater in alpha-stat than in pH-stat. However, cerebral oxygenation and brain tissue oxygen saturation were better in pH-stat than in alpha-stat during profound hypothermia. PH-stat strategy provided much more oxygen to brain tissue before deep hypothermic circulatory arrest.
authors.affiliation: Department of Cardiothoracic Surgery, Sir Run Run Shaw Hospital, Zhejiang University, Hangzhou 310016, China. zhijunli833@hotmail.com
authors.forename: Zhi-jun
authors.initials: ZJ
authors.lastname: Li
authors.forename: Xiao-mei
authors.initials: XM
authors.lastname: Yin
authors.forename: Jian
authors.initials: J
authors.lastname: Ye
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity / Q000502:physiology; D001921:Brain / Q000098:blood supply* / Q000502:physiology*; D001923:Brain Chemistry; D002315:Cardiopulmonary Bypass / Q000379:methods*; D002560:Cerebrovascular Circulation / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D007036:Hypothermia, Induced / Q000379:methods*; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D013552:Swine
chemical_list: D010100:Oxygen