[Spontaneous ventilation in anesthesia. Introduction].

The "ventilatory requirement" can be measured in every conscious subject. But it cannot be appreciated under general anaesthesia. General anaesthesia produce a difference between the amount of spontaneous breathing of the subject and his "ventilatory requirement". A metabolic debt can appear without ventilatory compensation. So spontaneous breathing is never indicated during general anaesthesia. It can be tolerated in some technical situations when controlled breathing is impossible.