Abstract: A medical ventilator system is disclosed which automatically controls and modifies the oxygen support provided to the patient. The system includes a source of pressurized oxygen and a fluid conduit extending between the pressurized oxygen source and a patient. A valve is fluidly connected in series with the conduit which is variably controllable to vary the oxygen support for the patient. A pulse oximeter provides an SpO2 signal representative of the blood saturation of the patient. A controller is responsive to the magnitude of the SpO2 signal as well as the rate of change of the SpO2 signal for varying the oxygen support (FiO2) to the patient by variably actuating the valve. Preferably, the controller utilizes fuzzy logic to determine the proper oxygen support for the patient.