A system for delivering a liquid pulmonary surfactant to spontaneously breathing patients, comprising: - i) a catheter adapted to reach the pharyngeal region of the patient, the catheter including at least a first channel being adapted to convey in the patient's pharyngeal region a flow of liquid pulmonary surfactant, - ii) first pump means connected to a first end of the at least first channel, adapted to create a pressure which pushes the column of liquid pulmonary surfactant towards the second end of the at least first channel; - iii) breathing detecting means, for measuring a value indicative of whether the patient is in an inspiration or in an expiration phase; - iv) pressure detecting means connected to the first channel for measuring a value indicative of the pressure of the liquid pulmonary surfactant; - v) a microprocessor configured to selectively activate the first pump means according to signals received from the breathing detecting means and the pressure detecting means, so that the first pump means are activated only during inspiration phase and the flow produced by the first pump means is adapted to counterbalance the delay induced by the hydraulic impedance of the system; characterized in that the first pump means includes a volumetric pump and the hydraulic impedance is estimated according to the measured value of the pressure in the first channel and the volume delivered by the pump; wherein adapting the flow produced by the first pump means includes adapting the flow according to a function having a plurality of predetermined sets of coefficients, each set of coefficients being associated to a range of values of the estimated hydraulic impedance. - i) a catheter adapted to reach the pharyngeal region of the patient, the catheter including at least a first channel being adapted to convey in the patient's pharyngeal region a flow of liquid pulmonary surfactant, - ii) first pump means connected to a first end of the at least first channel, adapted to create a pressure which pushes the column of liquid pulmonary surfactant towards the second end of the at least first channel; - iii) breathing detecting means, for measuring a value indicative of whether the patient is in an inspiration or in an expiration phase; - iv) pressure detecting means connected to the first channel for measuring a value indicative of the pressure of the liquid pulmonary surfactant; - v) a microprocessor configured to selectively activate the first pump means according to signals received from the breathing detecting means and the pressure detecting means, so that the first pump means are activated only during inspiration phase and the flow produced by the first pump means is adapted to counterbalance the delay induced by the hydraulic impedance of the system; characterized in that the first pump means includes a volumetric pump and the hydraulic impedance is estimated according to the measured value of the pressure in the first channel and the volume delivered by the pump; wherein adapting the flow produced by the first pump means includes adapting the flow according to a function having a plurality of predetermined sets of coefficients, each set of coefficients being associated to a range of values of the estimated hydraulic impedance. <EOS>