title: Relative changes in cerebral blood flow during cardiac operations using xenon-133 clearance versus transcranial Doppler sonography.
abstract: BACKGROUND
  Changes in cerebral blood flow (CBF) during cardiac operations have implications in terms of postoperative neurologic and neuropsychological dysfunction. Current techniques of CBF measurement are cumbersome and invasive. Transcranial Doppler sonography offers a noninvasive means of assessing changes in CBF. The aim of this study was validation of this technique with existing methods of CBF measurement during cardiac operations.
  
  
  METHODS
  We compared the changes in CBF using xenon-133 clearance with changes in middle cerebral artery velocity by transcranial Doppler sonography (VMCA) using pH-stat and alpha-stat acid-base management during cardiopulmonary bypass. Measurements were taken (1) before bypass, (2) at 28 degrees C on bypass, (3) at 37 degrees C on bypass, and (4) after bypass. Relative changes in CBF and VMCA, calculated as the percent change from the prebypass baseline value normalized to 100%, were used in this analysis.
  
  
  RESULTS
  During the hypothermic phase of cardiopulmonary bypass, CBF and VMCA increased by 45.9% and 51.8%, respectively (p < 0.001), during pH-stat acid-base management but decreased by only 26.4% and 22.4%, respectively (p < 0.0001), during alpha-stat acid-base management. Linear regression analysis of the absolute changes in CBF (mL . 100 g-1 . min-1) and VMCA (cm/s) showed a significant correlation (r = 0.60; r2 = 0.36; p < 0.0001), but a better correlation was obtained when relative changes in CBF and VMCA were compared (r = 0.89; r2 = 0.79; p < 0.0001).
  
  
  CONCLUSIONS
  Measurements of VMCA, expressed as relative changes of a pre-cardiopulmonary bypass level (using the noninvasive transcranial Doppler sonographic technique), can be used to examine CBF changes during cardiopulmonary bypass.
authors.affiliation: Department of Cardiac Surgical Research, Rayne Institute, St. Thomas' Hospital, London, United Kingdom.
authors.forename: U H
authors.initials: UH
authors.lastname: Trivedi
authors.forename: R L
authors.initials: RL
authors.lastname: Patel
authors.forename: M R
authors.initials: MR
authors.lastname: Turtle
authors.forename: G E
authors.initials: GE
authors.lastname: Venn
authors.forename: D J
authors.initials: DJ
authors.lastname: Chambers
mesh_terms: D000136:Acid-Base Equilibrium; D001783:Blood Flow Velocity; D002315:Cardiopulmonary Bypass; D002493:Central Nervous System Diseases / Q000517:prevention & control; D002560:Cerebrovascular Circulation / Q000502:physiology*; D001026:Coronary Artery Bypass; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D011183:Postoperative Complications / Q000517:prevention & control; D017585:Ultrasonography, Doppler, Transcranial; D014980:Xenon Radioisotopes
chemical_list: D014980:Xenon Radioisotopes