title: Mild and moderate hypothermia (alpha-stat) do not impair the coupling between local cerebral blood flow and metabolism in rats.
abstract: OBJECTIVE
  The effects of hypothermia on global cerebral blood flow (CBF) and glucose utilization (CGU) have been extensively studied, but less information exists on a local cerebral level. We investigated the effects of normothermic and hypothermic anesthesia on local CBF (LCBF) and local CGU (LCGU).
  
  
  METHODS
  Thirty-six rats were anesthetized with isoflurane (1 MAC) and artificially ventilated to maintain normal PaCO(2) (alpha-stat). Pericranial temperature was maintained normothermic (37.5 degrees C, n=12) or was reduced to 35 degrees C (n=12) or 32 degrees C (n=12). Pericranial temperature was maintained constant for 60 min until LCBF and LCGU were measured with autoradiography. Twelve conscious rats served as normothermic control animals.
  
  
  RESULTS
  Normothermic anesthesia significantly increased mean CBF compared with conscious control animals (29%, P<0.05). Mean CBF was reduced to control values with mild hypothermia and to 30% below control animals with moderate hypothermia (P<0.05). Normothermic anesthesia reduced mean CGU by 44%. No additional effects were observed during mild hypothermia. Moderate hypothermia resulted in a further reduction in mean CGU (41%, P<0.05). Local analysis showed linear relationships between LCBF and LCGU in normothermic conscious (r=0.93), anesthetized (r=0.92), and both hypothermic groups (35 degrees C r=0. 96, 32 degrees C r=0.96, P<0.05). The LCBF-to-LCGU ratio increased from 1.5 to 2.5 mL/micromol during anesthesia (P<0.05), remained at 2.4 mL/micromol during mild hypothermia, and decreased during moderate hypothermia (2.1 mL/micromol, P<0.05).
  
  
  CONCLUSIONS
  Anesthesia and hypothermia induce divergent changes in mean CBF and CGU. However, local analysis demonstrates a well-maintained linear relationship between LCBF and LCGU during normothermic and hypothermic anesthesia.
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Faculty of Clinical Medicine Mannheim, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Krafft
authors.forename: T
authors.initials: T
authors.lastname: Frietsch
authors.forename: C
authors.initials: C
authors.lastname: Lenz
authors.forename: A
authors.initials: A
authors.lastname: Piepgras
authors.forename: W
authors.initials: W
authors.lastname: Kuschinsky
authors.forename: K F
authors.initials: KF
authors.lastname: Waschke
mesh_terms: D000136:Acid-Base Equilibrium; D000768:Anesthesia, General; D000769:Anesthesia, Inhalation; D000818:Animals; D001345:Autoradiography; D001831:Body Temperature; D001921:Brain / Q000378:metabolism*; D002245:Carbon Dioxide / Q000097:blood; D002560:Cerebrovascular Circulation; D003243:Consciousness; D004734:Energy Metabolism; D005947:Glucose / Q000378:metabolism*; D007036:Hypothermia, Induced; D007530:Isoflurane; D008297:Male; D010100:Oxygen / Q000097:blood; D010313:Partial Pressure; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D002245:Carbon Dioxide; D007530:Isoflurane; D005947:Glucose; D010100:Oxygen