A ventilator (100; 1100) to ventilate an airway (112; 1112) of a patient, the ventilator (100; 1100) comprising: a conduit (114; 1114) having an inlet (114a; 1114a) in fluid communication with a patient port (114b; 1114b), said patient port (114b; 1114b) being configured to be fluidly connected to an airway (112; 1112) of a patient; a gas delivery element (116; 1116) fluidly connected to said inlet (114a; 1114a) and configured for selectively delivering fresh respiratory gas into the conduit (114; 1114); a valve (118; 1162) fluidly connected to said conduit (114; 1114), said valve (118; 1162) being selectively operable to vent the conduit (114; 1114) and thereby evacuate used respiratory gas via the patient port (114b; 1114b); and a controller (120; 1120) configured to alternatingly control the gas delivery element (116; 1116) and the valve (118; 1162) in a series of respiration cycles, wherein each respiration cycle includes the delivery of a main volume (Vm) of fresh respiratory gas into the conduit (114; 1114), followed by the evacuation of a corresponding volume (Vm') of used respiratory gas, said controller (120; 1120) being further configured to alternatingly control the gas delivery element (116; 1116) and the valve (118; 1162) in a series of subcycles during a corresponding one of the respiration cycles, wherein the valve is moved to open position whenever a main or an auxiliary evacuation of used air occurs, otherwise the valve remains closed so that fresh air is delivered into the airway of the patient, wherein each subcycle includes the delivery of an auxiliary volume (Va) of fresh respiratory gas into the conduit (114; 1114), followed by the evacuation of a volume (Va') of used respiratory gas corresponding to the auxiliary volume (Va), the auxiliary volume (Va) being smaller than, and distinct from, the main volume (Vm), wherein the gas delivery element has a moving element displaceable between first and second positions corresponding to either the main volume (Vm) or auxiliary volume (Va). a conduit (114; 1114) having an inlet (114a; 1114a) in fluid communication with a patient port (114b; 1114b), said patient port (114b; 1114b) being configured to be fluidly connected to an airway (112; 1112) of a patient; a gas delivery element (116; 1116) fluidly connected to said inlet (114a; 1114a) and configured for selectively delivering fresh respiratory gas into the conduit (114; 1114); a valve (118; 1162) fluidly connected to said conduit (114; 1114), said valve (118; 1162) being selectively operable to vent the conduit (114; 1114) and thereby evacuate used respiratory gas via the patient port (114b; 1114b); and a controller (120; 1120) configured to alternatingly control the gas delivery element (116; 1116) and the valve (118; 1162) in a series of respiration cycles, wherein each respiration cycle includes the delivery of a main volume (Vm) of fresh respiratory gas into the conduit (114; 1114), followed by the evacuation of a corresponding volume (Vm') of used respiratory gas, said controller (120; 1120) being further configured to alternatingly control the gas delivery element (116; 1116) and the valve (118; 1162) in a series of subcycles during a corresponding one of the respiration cycles, wherein the valve is moved to open position whenever a main or an auxiliary evacuation of used air occurs, otherwise the valve remains closed so that fresh air is delivered into the airway of the patient, wherein each subcycle includes the delivery of an auxiliary volume (Va) of fresh respiratory gas into the conduit (114; 1114), followed by the evacuation of a volume (Va') of used respiratory gas corresponding to the auxiliary volume (Va), the auxiliary volume (Va) being smaller than, and distinct from, the main volume (Vm), wherein the gas delivery element has a moving element displaceable between first and second positions corresponding to either the main volume (Vm) or auxiliary volume (Va). <EOS>