Respiratory management of intubated patients is a complex problem, even if airway management, sedation, and infection control are excluded and only the limited problem of "how to set a ventilator" is considered. Four dimensions shape the overall strategy for setting a ventilator: time, physiologic task, primary lung disease, and general therapeutic approach. Initiation (start-up), maintenance, and weaning are the principal dimensions in time. This article discusses the closed-loop control method.