Thermogard and rewarming catheter. (a) The Thermogard XP® system, which remotely senses changes in the patient's core temperature, automatically adjusts this to the target set by the use of a catheter incorporating circulating saline (reprinted courtesy of AsahiKASEI ZOLL Medical). The machine acts as a thermostat for core body temperature control, with a user-selected target temperature (31°C–38°C). Sterile saline from a standard 500-mL hanging bag is actively pumped through the machine and the intravascular catheter balloons in a closed loop at 200–240 mL/min, depending on the catheter type. Within the machine, the saline passes first through an air trap, followed by passing through a metal heat exchanger coil submerged in a temperature-controlled coolant well containing a mixture of propylene glycol and distilled water. The saline then circulates through balloons on the intravascular surface of one of the specially designed central venous catheters at a temperature of 0°C to 42°C to deliver or remove heat from the bloodstream. (b) The Cool Line® catheter is inserted into the common femoral vein and lodges in the inferior vena cava. Saline flow within the balloon creates a proprietary vortex flow pattern, which maximizes heat exchange with blood as it passes through (reprinted courtesy of AsahiKASEI ZOLL Medical).