Comparative exergy analysis of therapeutic hypothermia techniques

Abstract

Therapeutic hypothermia is defined as the induction of a lowered core body temperature. Over the last decades it has been applied for treating conditions that lead to cell and tissue damage caused by ischemia, including traumatic brain injury, stroke and cardiac arrest giving the patient best chances of survival with a neurological recovery. It is also used during surgeries and circulatory arrest. In this article the temperature of hypothermia is 32°C, which is considered mild temperature (32-35°C). In this paper, three types of mild hypothermia induction were considered, among them: external blood cooling, catheter insertion and water bath. Hence, energy and exergy analysis is performed to determine the clinical effectiveness of this therapy and to evaluate the best tests parameters. To this aim, it is calculated the energy and exergy transfer to environment, the metabolism (on energy and exergy basis) and the body energy and exergy variation over time due to transient environmental conditions. From these results it is possible to calculate the internal temperature of the body (represented by the tympanic temperature), destroyed exergy and exergy efficiency. Moreover it is proposed an exergy indicator which takes into account the ability of a given technique to change the exergy of the body. Results indicate that therapeutic hypothermia takes the subject to a state of lower destroyed exergy and higher body exergy efficiency. In comparison with the other two techniques, the external blood cooling achieves core temperature closer to 32°C, with lower destroyed exergy and higher exergy efficiency. The exergy indicator shows that lower rates of cooling lead to a better transformation of the exergy removed from the body into variation of the body exergy.

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