PARIS (AFP) - Emerging from an extended, drug-induced coma, like the one Michael Schumacher was placed in after a ski accident, could take several days or not happen at all, medical experts say.
Doctors started on Thursday to try and coax the Formula One legend out of an artificial deep sleep he was placed in after a near-fatal ski fall in December.
After a progressive reduction of the sedative dose, it can take several more days for the last drug traces in a patient's system to disappear, according to Gerard Audibert, a neurosurgeon at the University Hospital in Nancy, eastern France.
"There is a grey zone (between wake and sleep) that lasts several days, but it varies from one patient to another," he told AFP.
But awakening is not guaranteed.
"The patient may well stay in a coma," said Dr Audibert.
When it does happen, the awakening is always "visible", according to Parisian anaesthesiologist Bernard Vigue: "the patient opens his eyes or moves a bit".
The purpose of an induced coma is to allow the brain to rest so as to lower the pressure inside the skull caused by bruising and bleeding in the brain.
Once the pressure had been lowered and stabilised, doctors can start lifting an induced coma, said Dr Audibert.
Also factored into the decision is the patient's vital functions and ability to breathe independently - all artificial coma patients require a ventilator.
Doctors would now watch the patient for any response to external stimuli like voice commands, while also monitoring his brain with scanners.
A patient's loved ones play a crucial role at this stage by helping to coax the patient out of sleep, say the experts - also later to help stimulate the brain back to health.
Dr Vigue said Schumacher could have months, if not years, of therapy ahead of him.
"Recovery can be a very long road. In some case, patients improve between a year and three years later," he said.
Schumacher hit his head against a rock when he fell while skiing in the French Alps.