Doctors successfully performed a tracheotomy on Israeli Prime Minister Ariel Sharon Sunday to help wean him off a respirator that has been helping him breathe since he suffered a massive stroke 11 days ago.

The hospital where the 77-year-old Israeli leader is being treated also said a brain scan performed before the surgery showed no change in his condition.

Sharon remained in critical but stable condition ahead of the surgery, the hospital said Sunday in a statement. In the procedure, doctors cut a small hole in his neck to insert a tube directly into his windpipe.

Outside experts said the procedure is necessary because the plastic tube connecting his windpipe with the respirator will start to cause him damage if it remains in for much longer.

Sharon's comatose state and that he is undergoing the tracheotomy do not bode well for the prime minister's future, said Dr. Philip Stieg, chair of neurosurgery at the Weill-Cornell Medical College in New York.

It is becoming more probable as time passes that Sharon will either remain in a vegetative state or have low abilities to think and reason, said Stieg, who is not involved in Sharon's care.

"It suggests that the brain damage is as serious as we thought it was based on earlier reports and now its all playing out," Stieg said. "He's not turning the corner, he's not waking up ... they're having to do more things to keep him alive."

Dr. Maurizio Miglietta, chief of trauma and critical care at the New York University's School of Medicine, said a tracheotomy is a fairly simple, risk-free procedure that could take just 10 minutes. The risks of infection or a negative reaction to the general anesthetics are fairly low, he said.

Miglietta said it may be easier for doctors to wean Sharon off the sedatives because he will no longer have the uncomfortable breathing tube in his windpipe.

Doctors said Saturday that Sharon, who has been unconscious since the stroke, had activity on both sides of his brain.

Last week, doctors began weaning Sharon from the sedatives that had kept him in an induced coma to give his brain time to heal from the stroke and the surgeries that followed. By Saturday, he was only receiving light sedation, but remained unconscious.

Earlier Sunday, newspapers and radio stations reported Israel's Attorney General Meni Mazuz said he would notify Ehud Olmert that he will continue to hold the title of acting prime minister until the country's March 28 elections.

Mazuz has decided to continue defining Sharon as temporarily incapacitated, according to the media reports. If Mazuz were to declare Sharon permanently incapacitated, government ministers would have to choose an acting prime minister within 100 days of Olmert's Jan. 4 takeover from Sharon.

A declaration of permanent incapacitation would be irreversible.