Modeling patient temperature for improved thermal management during surgery

This paper describes the first results of numerical simulations modeling the whole-body temperature distribution inanaesthetised patients. Physical heat transfer is accounted for in a multi-segment model of the body, the modeledthermoregulation aims to maintain normal core temperature, and the administration of anaesthetics impact on thenormal thermoregulatory changes in vasodilatation, vasoconstriction, and shivering. The passive and normal activesystems devised by Fiala form the core of the model. In addition extra parameters have been introduced that modify thenormal thermoregulation. Specifically, temperature thresholds for the different thermoregulatory responses werechanged, and skin blood flow between thresholds was increased. The redistribution of heat caused by generalanaesthesia is hereby reproduced. The aim was to develop the concepts that will enable the development of a realisticthermal model of the anaesthetic patient. For this goal extensive validation experiments are planned. Here, it was triedto keep the model as simple as possible and to gain insight in changes in thermoregulation. The mathematical model hasbeen used to mimic a surgical procedure with use of a Heart Lung Machine (HLM). It was found that an afterdrop ofthe core temperature such as sometimes observed after decoupling from the HLM can be easily modeled.