A delta-wave inducer
A delta-wave inducer is used during an operation to keep the patient asleep, it also increases the body's natural endorphin production to help accelerate the healing process.
In 2370, Bashir used a delta-wave inducer on Jadzia Dax during the operation to remove the Dax symbiont and place it in its new host, Verad. (DS9: "Invasive Procedures")