Pathophysiology of the Central Nervous System During Hypothermia
The hypothermic state may be divided into 4 stages: clinical, surgical, deep or profound, and frozen or supercooled. The clinical stage extends from 35° to 32° C, surgical from 32° to 25° C, deep or profound from 25° to 0° C, and the frozen or supercooled
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Pathophysiology of the Central Nervous System During Hypothermia* By
H. L. Rosomoff With 9 Figures
The hypothermic state may be divided into 4 stages: clinical, surgical, deep or profound, and frozen or supercooled. The clinical stage extends from 35° to 32° C, surgical from 32° to 25° C, deep or profound from 25° to 0° C, and the frozen or supercooled from 0° to _8° C. Each stage has characteristic physiological activities, and each, within prescribed limits, is compatible with survival and restoration of complete integrity upon rewarming. It is clear that the low temperature slows the rate of cellular processes and modifies the action of metabolities and other substances. This is not necessarily harmful, as long as anoxia and chemical imbalance do not develop. The basic physicochemical considerations in hypothermia relate to the laws governing the dependence of cellular activities and their enzymatic reactions on temperature, ions, metabolites, and drugs [1]. Of particular importance are such interdependent cellular phenomena as excitability, rhythmicity, and contractility. When the temperature is lowered, the rate of activity of each process is reduced in accordance with its temperature coefficient. Therefore, the effectiveness of an interdependent system at a given temperature depends on the relative actual rates of the processes within that system, and their respective temperature coefficients. In terms of temperature coefficient, reactions are classified as having a QIO of 1, 2, or 3, indicating that the rates of reaction involved change in this proportion for a 10° C change in tem-
* This study was supported by Research Grant B-2469 from the National Institute of Neurological Diseases and Blindness, U. s. P. H. S.
P. E. Maspes et al. (eds.), Hypothermia in Neurosurgery © Springer-Verlag/Wien 1964
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H. L. Rosomoff:
perature. That is, in hypothermia with a reduction of temperature of 10° C, the reaction rate of a given process will decrease by a factor of 1, 2, or 3, depending on its temperature coefficient. In general, metabolic and rhythmical processes have a QI0 of 3, contraction a QI0 of 2, and most physical processes, such as diffusion, a QI0 of 1. Accordingly, when the temperature is lowered, the metabolic and rhythmical processes decrease 2 to 3 times as much as the rate of diffusion of metabolites. Therefore, it is perfectly possible for cardiac rhythm to cease, as it usually does between 10° and 25° C, and cellular activity to continue on to a much lower temperature without ill ~ffect, provided anoxia does not supervene. Thus, the control of induced hypothermia rests on an understanding of the cellular phenomena involved, the susceptibility of the systems to temperature, ions, and drugs, and our ability to regulate artificially the activity of these processes by modifying the cellular environment. Little is known about the details of metabolic activity during hypothermia, except for studies of oxygen consumption. The measurement of oxygen consumption is a rather gross index of metabolic activ
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