The 88-year-old Inouye is the country's longest serving senator, now completing his 50th year in the chamber.
Spokesman Peter Boylan said Sunday the senator remains hospitalized at Walter Reed National Military Medical Center, where he was taken earlier this month so doctors could observe him and monitor his oxygen intake.
Boylan says Inouye is "fighting respiratory complications" but is in stable condition and communicating with his doctors and family. Boylan adds: "At this time, there is no timetable for his release."
Inouye is a decorated World War II veteran and has long been a force in Hawaii politics. He serves as chairman of the Appropriations Committee and is the Senate's president pro tempore, third in the presidential line of succession.