A device, comprising: an elongate sensor support device adapted to be inserted into a patient and having a plurality of temperature sensors connected to it along its length; and a controller adapted to receive signals from the sensors and control - at least one of a) a temperature of an infusate infused into the patient through an insertion device in a downstream direction, b) an infusion rate of the infusate, and c) a volume of the infusate, the control of a,b,c being in accordance with - at least a temperature of a blood and infusate mixture downstream relative to an infusate exit location of the insertion device while the insertion device is placed in a blood vessel of a patient with a downstream flow of blood for infusion of the infusate characterised in that the controller being further adapted to control - at least one of b) an infusion rate of the infusate, and c) a volume of the infusate, the control of b,c being in accordance with aplateauingof a native vessel flow rate in the blood vessel detected by the controller, wherein the native vessel flow rate in the blood vessel being calculated by the formula infusion rate*(T1-T 2)/(T 4 -T 1), where T1 is a temperature of the blood and infusate mixture downstream the exit location, T 2 is a temperature of the infusate at least one of at and adjacent the exit point, and T4 is the core body temperature of the patient. an elongate sensor support device adapted to be inserted into a patient and having a plurality of temperature sensors connected to it along its length; and a controller adapted to receive signals from the sensors and control - at least one of a) a temperature of an infusate infused into the patient through an insertion device in a downstream direction, b) an infusion rate of the infusate, and c) a volume of the infusate, the control of a,b,c being in accordance with - at least a temperature of a blood and infusate mixture downstream relative to an infusate exit location of the insertion device while the insertion device is placed in a blood vessel of a patient with a downstream flow of blood for infusion of the infusate characterised in that the controller being further adapted to control - at least one of b) an infusion rate of the infusate, and c) a volume of the infusate, the control of b,c being in accordance with - at least one of a) a temperature of an infusate infused into the patient through an insertion device in a downstream direction, b) an infusion rate of the infusate, and c) a volume of the infusate, the control of a,b,c being in accordance with a) a temperature of an infusate infused into the patient through an insertion device in a downstream direction, b) an infusion rate of the infusate, and c) a volume of the infusate, the control of a,b,c being in accordance with - at least a temperature of a blood and infusate mixture downstream relative to an infusate exit location of the insertion device while the insertion device is placed in a blood vessel of a patient with a downstream flow of blood for infusion of the infusate characterised in that the controller being further adapted to control - at least one of b) an infusion rate of the infusate, and c) a volume of the infusate, the control of b,c being in accordance with b) an infusion rate of the infusate, and c) a volume of the infusate, the control of b,c being in accordance with aplateauingof a native vessel flow rate in the blood vessel detected by the controller, wherein the native vessel flow rate in the blood vessel being calculated by the formula infusion rate*(T1-T 2)/(T 4 -T 1), where T1 is a temperature of the blood and infusate mixture downstream the exit location, T 2 is a temperature of the infusate at least one of at and adjacent the exit point, and T4 is the core body temperature of the patient.