Mapleson D or Bain anesthesia circuits are semi-closed breathing systems widely used for controlled ventilation during general anesthesia. They consist of lightweight, flexible tubing that supports easy handling in ORs and ICUs. The coaxial design of Bain circuits enhances warming of inspired gases, reducing heat loss in patients. Suitable for both adult and pediatric airway management depending on circuit size. Used during surgeries requiring continuous oxygen and anesthetic gas delivery. Compatible with standard ventilators and manual resuscitation bags. Color-coded components simplify setup and reduce connection errors. Available in reusable or sterile disposable variants. Provide low resistance to airflow for safe ventilation. Classified under CDSCO Class B for anesthesiology devices in India.