Direct extravascular brain cooling in the normothermic animal

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Abstract
Direct extravascular brain cooling is defined as one type of local surface cooling. Existing technics and observations made are reviewed and 2 main fields of interest related to such technics are defined-namely, that of the investigator searching for technics allowing reversible depression of brain function and that of the clinician seeking applications in surgery and medicine. Open and closed methods of local brain cooling are described, with methods and results of precise measurement of brain temperatures. Results are given for cooling experiments in 20 cats, 6 monkeys, and 6 rabbits. A variety of devices are described and the methods preferred are for clinical purposes, the open or closed surface or ventricular irrigation technics, or both; and for investigative purposes, the gas method. The protective effect of such hypothermia against cerebral ischemia is demonstrated in rabbits. The abolition of consciousness and superficial reflexes by surface and ventricular perfusion was demonstrated in the monkey. Evidence revealing poor insulating properties of the head is reviewed, and a modification of the "core-shell" theory in hypothermia is offered for the head and intracranial contents. The "safest" temperature for brain hypothermia is discussed in terms of quality of survival rather than quality of cooling. On the basis of such data, it is suggested that extravascular local brain cooling is physiologically a more justifiable technic. The advantages of this method are reviewed, its disadvantages contrasted with other technics of hypothermia, and applications are suggested in clinical medicine and surgery and in physiology and psychology.

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