The present method, system and device relate to a ventilatory assistance system comprising a ventilatory assistance device, which comprises a tube on which a tubular nozzle is integrally mounted, and a respiratory gas supply duct able to connect said tubular nozzle to a source of respiratory gas. The present ventilatory assistance system further comprises obstacle forming means counteracting against assembling a connecting member of an external medical device to said tubular nozzle, when the latter is connected to said source of respiratory gas by means of said supply duct.
