Cerebral edema - serious swelling of the brain, which resulted from the cardiac arrest on Tuesday night when Nirbhaya was still in India, along with severe infections, finally proved fatal.
A CT scan that was conducted after Nirbhaya reached Singapore showed that blood loss to her brain caused during the three-minute period when doctors at Safdarjung hospital in Delhi had failed to find a pulse or blood pressure, led to the brain edema - a dangerous condition where the brain's water content rises, causing the pressure to rise in the skull.
This cuts off oxygen supply as the blood vessels become squeezed. Cerebral edema is a medical emergency that can even lead to death as brain cells become damaged and die.
Prime minister Manohan Sngh said he was "deeply saddened to learn that the unfortunate victim of the brutal assault that took place on December 16 in New Delhi had succumbed to the grievous injuries she suffered following that attack. "I join the nation in conveying to her family and friends my deepest condolences at this terrible loss."
Singh said: "I want to tell them and the nation that while she may have lost her battle for life, it is up to us all to ensure that her death will not have been in vain. We have already seen the emotions and energies this incident has generated. These are perfectly understandable reactions from a young India and an India that genuinely desires change. It would be a true homage to her memory if we are able to channelize these emotions and energies into a constructive course of action."
According to Singh, the need of the hour is a dispassionate debate and inquiry into the critical changes that are required in societal attitudes.
He said that the government is examining, on priority basis, the penal provisions that exist for such crimes and measures to enhance the safety and security of women.
"I hope that the entire political class and civil society will set aside narrow sectional interests and agenda to help us all reach the end that we all desire - making India a demonstrably better and safer place for women to live in," Singh said.
Nirbhaya's health started to slide from Friday evening (6.30 pm IST) when she suffered multiorgan failure.
Doctors informed her family members that Nirbhaya's condition had seriously deteriorated as she was put on maximum artificial ventilation support, optimal antibiotic doses as well as stimulants which would help maximise her body's capability to fight infections.
In the early hours of Saturday, Mount Elizabeth hospital issued a fresh statement announcing the worst.
The hospital said: "In relation to the young female patient from Delhi who was assaulted in a bus, and who was transferred from a hospital in India to receive further treatment at Mount Elizabeth Hospital in Singapore on December 27, we are very sad to report that the patient passed away peacefully at 4.45am (Singapore time) on December 29. Her family and officials from the high commission of India were by her side. The patient had remained in an extremely critical condition since admission to Mount Elizabeth hospital in the morning of Dec 27."
According to the hospital, despite all efforts by a team of eight specialists at Mount Elizabeth hospital to keep her stable, her condition continued to deteriorate and she suffered from severe organ failure following serious injuries to her body and brain.
"She was courageous in fighting for her life for so long against the odds but the trauma to her body was too severe for her to overcome," Dr Kelvin Loh, CEO of the hospital said.
Critical care specialist Dr Yatin Mehta from Medanta hospital, who had accompanied Nirbhaya to Singapore, told TOI on his return to India on Saturday morning that the swelling of the brain finally took her life.
"A fresh episode of cardiac arrest resulted in multiorgan dysfunction syndrome. Her injuries were too severe. While being transported to Singapore, her oxygen requirements increased by 70%. We had carried 8 oxygen cylinders as standby, each capable of running for two hours. Six additional batteries were taken to ensure the machines ran fine during the flight. Her blood pressure fell to around 80 on route which we finally managed to bring back to normal. The injuries were horrendous," said Dr Mehta, who left for India from Singapore on Friday night when Nirbhaya was still alive, told TOI on his return.
Dr Mehta also added that Nirbhaya's organs weren't fit for donation as they were seriously infected.
"We spoke to the family very frankly last night. We told her father and brothers that she is critical and might not pull through. Her family was stoic and handled the eventuality i a very mature way," Dr Mehta said.