Sidestream EtCO2 sensors are used to measure the carbon dioxide (CO2) levels in a patient's breath during anesthesia or ventilation procedures. These sensors are located separate from the patient's airway and are connected to the breathing circuit through a sampling tube. They draw a small sample of the patient's exhaled breath away from the airway and analyze it to determine the CO2 concentration.

Sidestream sensors provide continuous monitoring of CO2 levels, allowing healthcare professionals to assess ventilation effectiveness and the patient's respiratory status, commonly used in critical care units and during procedures where endotracheal intubation is not required.