A respiratory gas conditioning system (100) and method. The system includes an inhale branch (IB), an exhale branch (EB), a low-dead-space heat and moisture exchanger (HME) (50), and a connector (70) for connecting the branches (IB, EB) to a patient (PZ). The system (100) is characterized in that the HME (50) is located close to a ventilator (60) and a water reservoir (RS) is located upstream from the HME (50) to moisture-enrich the gas exhaled by the patient (PZ) as it flows along the exhale branch (EB).