Prime Minister Ariel Sharon, comatose since a January 4 stroke, had surgery overnight to replace his breathing tube, according to a statement early Wednesday from the hospital where he is being treated. "The prime minister's condition continues to be critical and stable," the statement said. "The breathing tube was changed overnight due to a technical problem. The successful procedure was conducted in the operating room. The prime minister was taken back to his room in the morning." Sharon underwent a tracheotomy on Sunday.