She faced a crisis during the day after which doctors took an emergency decision and used endotracheal intubation to remove the fluid accumulation from her lungs and ease her breathing, doctors said.
The 82-year-old actress was suffering from breathing difficulties, doctors said
Sen's blood sugar level is under control, but oxygen saturation is fluctuating making it a cause for concern, they said, adding that her low food intake has made her weak.
She was also administered nebuliser, they said.
Her vital organs like kidney are, however, working properly, critical care specialist Dr Subrata Maitra said.
Senior physician Sukumar Mukherjee has also been consulted by the doctors.
Sen has been put on oral prescribed diet supplemented with peripheral parenteral nutrition and seen by Pawan Agarwal and Dhiman Ganguli.
A medical-team led by Dr Maitra is monitoring her condition 24x7.
The 82-year-old actress was admitted to Belle Vue clinic on December 23 following a respiratory tract infection.
As her health turned critical, West Bengal Chief Minister Mamata Banerjee, CPI(M) leader Robin Deb and monks from the Ramakrishna Mission in Belurmath and Narendrapur visited the super-speciality hospital.
Banerjee said, "This is a very sensitive period. We wish that she returns home fast."
Sen, who has lived the life of recluse for the last three decades, was the first Indian actress to win the best actress award internationally at the Moscow Film Festival.
She had starred in memorable Hindi films like Devdas, Aandhi and Saat Paake Bandha, Agnipariksha, Saptapadi and Deep Jwele Jai in Bengali.