Acta Anaesthesiol Scand 2007; 51: 872–879 Printed in Singapore. All rights reserved # 2007 The Authors Journal compilation # 2007 Acta Anaesthesiol Scand ACTA ANAESTHESIOLOGICA SCANDINAVICA doi: 10.1111/j.1399-6576.2007.01356.x Temperature gradient between brain tissue and arterial blood mirrors the flow-metabolism relationship in uninjured brain: an experimental study J. S OUKUP 1 , A. R IEGER 2 , C. HOLZ 2 , I. MIKO 4 , N. NEMETH 4 and M. M ENZEL 3 Department of 1 Anesthesiology and Intensive Care Medicine, and 2 Neurosurgery, Martin-Luther-University Halle-Wittenberg, Halle/Saale, 3 Department of Anesthesiology, Klinikum Wolfsburg, Germany and 4 Department of Operative Techniques and Surgical Research, University of Debrecen Medical and Health Science Center, Debrecen, Hungary Background:The purpose of the present experimental study was to determine the feasibility and usefulness of brain temperature measurement (T br ) and the calculated difference between brain temperature and arterial blood temperature (DT br-a ) in uninjured brain during variations of cerebral perfusion pressure (CPP) and concomitant changes of the regional cerebral blood flow (rCBF). Methods: Nine anaesthetized pigs were subjected to controlled CPP decrease to assess the lower cerebral autoregulation thresh- old. A parenchymal intracranial pressure (ICP) sensor combined with a microthermistor for temperature measurement, a minia- turized Clark-type electrode measuring brain tissue oxygenation (p ti O 2 ), a smallflexible intraparenchymal thermodilution probe for measuring rCBF and cerebral microdialysis were inserted carefully in the frontal white matter. Results: Analysing the p ti O 2 during controlled CPP decrease, we found significant breakpoints of p ti O 2 at a CPP of 40 mmHg and 20 mmHg,related to an rCBF of 20 ml/100 g/min and approx- imately 10 ml/100 g/min. Similarly,the relationship between DT br-a , and CPP or rCBF revealed a characteristic increase of DT br-a in the negative direction up to more than –0.30 8C assuming a strong flow dependency. Conclusion: The temperature difference between brain tissue and arterial blood DT br-a mainly reflects the cerebral blood flow–brain tissue oxygenation–metabolism relationship as far as the estima- tion of the individual lower cerebral autoregulation threshold. Accepted for publication 14 April 2007 Key words: Cerebral autoregulation; tissue oxygen; cerebral blood flow; brain temperature. # 2007 The Authors Journal compilation # 2007 Acta Anaesthesiol Scand D URING recentyears, technologieshave been developed to measure brain temperature directly.Consequently, direct measurement of brain tissue temperature has gained increasing interest in experimental studies and clinical practice as a moni- toring tool and as a therapeutic parameter in the context of neuroprotective measures (1–5). Regarding the efficiency of brain tissue tempera- ture monitoring,one could demonstrate that only brain temperature monitoring alone can reflect the real brain tissue temperature (6, 7). However, recently available data suggest that continuously measuring and analysing brain tissue temperature might be useful together with patients body temperature to assess the severity of injury, too (6, 8, 9). From this point of view, there is a potential need to establish reliable bed-side monitoring methods to characterize the individual brain temperature char- acteristics in patients after severe neuronal injury. The purpose of the present experimental study was to determine the feasibility and usefulness of brain temperature measurement (T br ) and the calculation of the difference between brain temperature and arterial blood temperature (DT br-a ) in uninjured brain during variations of cerebralperfusion pressure (CPP) and concomitantchangesin the regional cerebral blood flow (rCBF). Additionally, brain tissue oxygen monitoring and cerebral microdialysis were employed to achieve further information about the accompanying changes in cerebral tissue oxygena- tion and cerebral metabolism. Materials and methods Nine domestic pigs (age: 3 months) weighing 29 to 35 kg were used in the animal study. All experiments were performed in accordance with the guidelines issued by the Committee ofAnimal Research at 872