This disclosure describes systems and methods for conducting and terminating spontaneous breathing trials on patients receiving mechanical ventilation. The disclosure describes a novel spontaneous breathing trial manager for a medical ventilator with rapid initiation and continuous monitoring of a patient's tolerance of the spontaneous breathing trial and displaying of that tolerance as a function of time, which provides for bedside adjustment of the spontaneous breathing trial parameters and automatic termination of a spontaneous breathing trial based on a time interval expiration or poor patient tolerance of the SBT.