Sterile saline is warmed (to a maximum temperature of 38 °C) in the external device and then pumped through the balloons coaxially mounted on the catheter, enabling direct warming of the blood. The catheter contains a temperature probe enabling a 'closed loop' temperature control system; the temperature is set at the desired level (the range of the device is 28-38°C, which may vary according to the installed software), after which the device warms the patient to this level by increasing or decreasing the temperature of the circulating saline. The core temperature is then maintained at the desired level for as long as the attending physician deems necessary. The catheter also has two ports for central venous access, which can be used to administer medication and/or for blood sampling.