Ventilator enables operator to enter into the microprocessor estimate of a patient's individual characteristic, such as weight, which the microprocessor uses to control delivered tidal volume and other parameters to match the patient. The operator can select one of several ventilator operational modes (intube, mask, CPR). Sensors input data to the microprocessor to maintain parameter optimizations and accuracy. Visual/audible alarms and tools activate when one or more parameters exceed or fail to exceed predetermined values for patient's weight. Manual over-ride is available. The ventilator has a quick start capability in which the operator turns on power, selects the automatic operating mode, enters patient's characteristic, selects control option starting automatic ventilation of proper volumes inhalation/exhalation periods, pressure, and oxy-air mixture.