Oxygenation status was evaluated in medetomidine-sedated dogs breathing room air (M) or 100 percent oxygen (MO2). Medetomidine (40 microg/kg IV) administration resulted in peripheral vasoconstriction and decreased venous saturation as measured by an increased oxygen extraction ratio in peripheral tissues. Providing 100 percent oxygen insufflation via face mask reduced desaturation by increasing oxygen content but did not prevent vasoconstriction or reduce the oxygen extraction ratio in peripheral tissues. Atipamezole (200 microg/kg IV) reversed medetomidine-induced vasoconstriction and increased oxygen supply to tissues as indicated by a lower tissue oxygen extraction ratio. The authors conclude that 100 percent oxygen insufflation via face mask during medetomidine sedation (40 micrograms/kg [corrected] IV) benefits tissue oxygenation in healthy dogs.