A patient treatment system and method comprising a patient circuit, a pressurizing flow module disposed in the patient circuit, a humidifier disposed in the patient circuit, a monitor, sensors within the patient circuit, and a processor. The patient circuit delivers a flo of gas from a gas source to an airway of a patient. The pressurizing flow module elevates the pressure of the gas within the patient circuit. The humidifier elevates the humidity of the gas in the patient circuit to a circuit humidity level. The monitor monitors at least on parameter of the gas from the gas source. The sensors generate corresponding signals that can be processed to estimate a rate at which vapor is added to the gas in the patient circuit.
