The indications for heliox during mechanical ventilation are lower-airway obstruction, especially with hypercarbia; need to enhance aerosol delivery to lung periphery; and need to facilitate weaning from mechanical ventilation. Certain ventilators perform relatively well with heliox and are not substantially affected by it. It is preferable to connect the heliox to the air inlet of the ventilator, because this results in more consistent delivery of oxygen and tidal volume. When administering heliox, pay close attention and directly monitor the actual tidal volume and fraction of inspired oxygen.