Abstract: A blood gas analyzer system for monitoring real-time blood gas conditions in a patient perfusion circuit during open-heart surgery and other extracorporeal blood flow situations. Sensing electrodes are employed in the blood flow path for sensing pH, pCO.sub.2, pO.sub.2 and temperature, and electrical circuitry is provided for generating and processing the sensed signal and also for computing a signal representing HCO.sub.3.sup.- ; also, these signals are monitored in real time. When situations of metabolic acidosis, metabolic alkalosis, respiratory acidosis or respiratory alkalosis occur, the system activates a corresponding alarm and automatically switches into a compensation mode of effect a change in pump speed, which in turn changes the delivery rate of oxygenated blood to the patient. When the blood gas level returns to normal, the pump speed is likewise automatically returned to a normal value.