This has been done to improve his breathing pattern, a hospital press release said adding that the actor was showing positive response to treatment.
A multi-disciplinary team of doctors is busy closely watching his vital parameters to assess benefits from multi-pronged treatment strategies, it said.
Doctors said he was responding well to treatment.
Rajinikant, who suffered from viral fever and exhaustion recently, was admitted to SRMU at suburban Porur days after he was discharged from another hospital where he had been treated for allergic bronchitis and viral fever.
He had suffered from exhaustion on Apr 29, the first day of the shoot of his new period film ''Rana'' co-starring Deepika Padukone, which is being directed by K S Ravikumar.
He was admitted to Isabel Hospital in the city and discharged the same day, only to be readmitted there on May 4 for allergic bronchitis and viral fever.
His family had last week dismissed reports that his health had deteriorated.