Device for the continuous monitoring of characteristic blood quantities in extracorporeal circulation circuit, said circuit comprising a venous line which conveys the blood from the patient to an oxygenator device and an arterial line which conveys the blood from the oxygenator back to the patient, comprising: - a sensor connected to the venous line and a sensor connected to the arterial line suitable for continuous measuring the quantities represented by venous saturation (SAT V) of the oxygen and by arterial saturation (SAT A) of the oxygen, respectively; - two sensors (12, 16) fitted in some points of the extracorporeal circuit, suitable for continuous measuring the quantities represented by blood flow (C.O.) and haemoglobin (Hb), respectively; - at least a sensor (18, 19) fitted in one point of the extracorporeal circuit, suitable for continuous measuring blood pressure; - means suitable for data entering by the operator; - a monitor having a micro processor and a display screen, said micro processor being suitable for receiving the data measured by said sensors (11, 12, 15, 16, 18, 19) and data entered by the operator to make them appear at least in part on said display screen, characterized by the fact that it comprises at least two sensors (9, 10) fitted in one point of the extracorporeal circuit, suitable for continuous measuring lactates and glycaemia respectively, said micro processor being suitable for lactates and glycaemia receiving the data measured by said sensors (9, 10) to make them appear on said display screen in numerical form and possibly also in graphic form, by the fact that said microprocessor has means suitable for calculating the quantity of the corporeal surface of the patient, the quantity of transported oxygen, the quantity of oxygen consumed at tissue level, the quantity of the fraction of extraction of the oxygen, the quantity of the systemic vascular resistance, the quantity of the cardiac index (C.I.), the quantity of the difference between two pressure values (ΔP) measured by two of said blood pressure sensors (18, 19) installed at distant points of the circuit,, making them appear on the display screen, said micro processor being programmed to display in numerical form on the display screen the values of all the quantities measured and calculated, and in graphic form, at least some of such values, that the micro processor has means suitable for calculating at least one indexed quantity D02i, V02i, 02ERi, SVRi corresponding to the quantities D02, V02, 02ER and SVR respectively, split up by the corporeal surface of the patient, and by the fact that the micro processor comprises means for displaying a diagram having in abscissa the quantity D02i and in ordinate the quantity V02i, wherein said display means are programmed to represent the lines indicating an increase in V02i with an increase of D02i with a first colour so as to highlight a dangerous situation and to represent the lines indicating a constant pattern of V02i with the increase of D02i with a second colour, different from said first colour, so as to highlight a safe situation. - a sensor connected to the venous line and a sensor connected to the arterial line suitable for continuous measuring the quantities represented by venous saturation (SAT V) of the oxygen and by arterial saturation (SAT A) of the oxygen, respectively; - two sensors (12, 16) fitted in some points of the extracorporeal circuit, suitable for continuous measuring the quantities represented by blood flow (C.O.) and haemoglobin (Hb), respectively; - at least a sensor (18, 19) fitted in one point of the extracorporeal circuit, suitable for continuous measuring blood pressure; - means suitable for data entering by the operator; - a monitor having a micro processor and a display screen, said micro processor being suitable for receiving the data measured by said sensors (11, 12, 15, 16, 18, 19) and data entered by the operator to make them appear at least in part on said display screen,