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(Stroke. 2000;31:1393.)
© 2000 American Heart Association, Inc.

Original Contributions

Mild and Moderate Hypothermia (-Stat) Do Not Impair the Coupling Between Local Cerebral Blood Flow and Metabolism in Rats

Peter Krafft, MD; Thomas Frietsch, MD; Christian Lenz, MD; Axel Piepgras, MD; Wolfgang Kuschinsky, MD Klaus F. Waschke, MD

From the Departments of Anesthesiology and Critical Care Medicine (P.K., T.F., C.L., K.F.W.) and Neurosurgery (A.P.), Faculty of Clinical Medicine Mannheim, and the Department of Physiology I (W.K.), University of Heidelberg, Germany.

Correspondence to Klaus F. Waschke, MD, Department of Anesthesiology and Critical Care Medicine, Faculty of Clinical Medicine Mannheim, University of Heidelberg, Theodor Kutzer Ufer 1-3, D-68167 Mannheim, Germany. E-mail km20{at}rumms.uni-mannheim.de

Background and Purpose—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 PaCO₂ (-stat). Pericranial temperature was maintained normothermic (37.5°C, n=12) or was reduced to 35°C (n=12) or 32°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°C r=0.96, 32°C r=0.96, P<0.05). The LCBF-to-LCGU ratio increased from 1.5 to 2.5 mL/µmol during anesthesia (P<0.05), remained at 2.4 mL/µmol during mild hypothermia, and decreased during moderate hypothermia (2.1 mL/µmol, 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.

Editorial Comment

Costantino Iadecola, MD, Guest Editor

Center for Clinical and Molecular Neurobiology, Departments of Neurology and Neuroscience University of Minnesota, Minneapolis, Minnesota