Installation (1, 2) for supplying gas to a patient, comprising: - an NO delivery device configured to supply an NO/N 2 gas mixture, comprising: ■ an NO injection line for conveying the NO/N 2 gas mixture, ■ a valve device arranged on the injection line in order to control the circulation of the NO/N 2 gas mixture in the injection line, ■ a backup line that connects fluidly to the injection line upstream and downstream of the valve device, said backup line comprising a backup solenoid valve and a flow rate control device, and ■ operating means configured to interact with the backup solenoid valve, the flow rate control device and the valve device, - a medical ventilator configured to supply a respiratory gas containing oxygen, - a patient circuit to which the NO delivery device and the medical ventilator are fluidly connected in order to supply said patient circuit with said NO/N 2 gas mixture and with said respiratory gas containing oxygen, and - a flow rate sensor configured to supply to the operating means of the NO delivery device at least one measurement signal representing at least one gas flow rate within the patient circuit, and in which in the event of the interruption of reception, by the operating means of the delivery device, of said at least one measurement signal supplied by the flow rate sensor: - the backup solenoid valve is configured to switch to an open position in order to allow the circulation of the NO/N 2 gas mixture in the backup line, - the valve device is configured to switch to a closed position in order to stop any circulation of gas in the injection line, and - the flow rate control device is configured to supply the NO/N 2 gas mixture at a pre-set backup gas flow rate, where said backup gas flow rate has been determined by the operating means on the basis of at least one measurement signal supplied by the flow rate sensor, before said interruption of reception of said signal, and pre-regulated by a command to the flow rate control device from said operating means, before said interruption of reception of said signal. - an NO delivery device configured to supply an NO/N 2 gas mixture, comprising: ■ an NO injection line for conveying the NO/N 2 gas mixture, ■ a valve device arranged on the injection line in order to control the circulation of the NO/N 2 gas mixture in the injection line, ■ a backup line that connects fluidly to the injection line upstream and downstream of the valve device, said backup line comprising a backup solenoid valve and a flow rate control device, and ■ operating means configured to interact with the backup solenoid valve, the flow rate control device and the valve device, ■ an NO injection line for conveying the NO/N 2 gas mixture, ■ a valve device arranged on the injection line in order to control the circulation of the NO/N 2 gas mixture in the injection line, ■ a backup line that connects fluidly to the injection line upstream and downstream of the valve device, said backup line comprising a backup solenoid valve and a flow rate control device, and ■ operating means configured to interact with the backup solenoid valve, the flow rate control device and the valve device, - a medical ventilator configured to supply a respiratory gas containing oxygen, - a patient circuit to which the NO delivery device and the medical ventilator are fluidly connected in order to supply said patient circuit with said NO/N 2 gas mixture and with said respiratory gas containing oxygen, and - a flow rate sensor configured to supply to the operating means of the NO delivery device at least one measurement signal representing at least one gas flow rate within the patient circuit, - the backup solenoid valve is configured to switch to an open position in order to allow the circulation of the NO/N 2 gas mixture in the backup line, - the valve device is configured to switch to a closed position in order to stop any circulation of gas in the injection line, and - the flow rate control device is configured to supply the NO/N 2 gas mixture at a pre-set backup gas flow rate, where said backup gas flow rate has been determined by the operating means on the basis of at least one measurement signal supplied by the flow rate sensor, before said interruption of reception of said signal, and pre-regulated by a command to the flow rate control device from said operating means, before said interruption of reception of said signal.