Research conducted on the application of external therapeutic hypothermia techniques has demonstrated promising outcomes, such as neuroprotection effects that considerably reduce mortality rates. One commonly employed method involves the assessment of body temperature using an external catheter. However, there is a problem to be tackled: tests for hypothermia induction cannot risk the well-being of a patient. The objective of the present study is to analyze the cooling rate of a catheter using CFD simulation with a specific geometry and evaluate the behavior of the human body during this cooling procedure by employing a validated human thermal model representing the human thermal and circulatory systems. The thermal model consists of four layers, with the central layer representing the human core and the others are, in order, muscle, fat, and skin. Then, each layer is associated with an equation derived from the First Law of Thermodynamics allowing for the calculation of heat transfer rates between the blood and the tissue. In the catheter simulation, commercially available software could generate data for subsequent calculations, including effectiveness and UA product. The results revealed that it is only possible to assess the target temperature with precise control of the saline solution flow rate and temperature. Additionally, this study represents a pioneer investigation into the behavior of the human body when using this technique with a defined geometry.