In a mainstream capnograph, the CO2 sensor is located between the endotracheal tube and the breathing circuit. In a sidestream capnograph, the sensor is located in the main unit and away from the airway. Between the endotracheal tube and the breathing circuit sits a sampling adapter that houses a tiny pump, which aspirates gas samples from the exhaled air. These samples travel through a 6 ft long capillary tube towards the main unit. The biggest advantage of sidestream capnographs is that they can be used on non-intubated subjects because the sampling of the expiratory gasses can be done via the nasal cavity using nasal adaptors.