Michael Schumacher at critical stage in treatment for head injury

Michael Schumacher, who suffered serious head injuries while skiing off-piste in the French Alps, is in intensive care at the University Hospital of Grenoble Photograph: Olycom SPA/REX

Doctors have reached a critical stage in their treatment of Michael Schumacher who suffered a serious head injury while skiing off-piste at the Méribel resort in the French Alps.

The former Formula One motor racing champion has been moved to an intensive care unit at the University Hospital of Grenoble where the priority is to prevent a dangerous build-up of pressure in his brain. Severe swelling stops blood flowing into the brain and starves it of oxygen, causing damage that can be fatal.

Schumacher was able to speak directly after the accident, but became agitated and fell into a coma soon after he arrived at Grenoble by air ambulance. He is now under anaesthetic to keep him in a coma and give his brain the best chance of recovery. Doctors performed emergency surgery on Schumacher to remove a blood clot that was pressing on his brain. They are now keeping him in a state of hypothermia, which cools the brain to 34 to 35C, to reduce pressure caused by the swelling of his brain.

Peter Andrews, professor of intensive care at Edinburgh University, who is leading the world's largest trial of hypothermia to reduce brain pressure, said a head injury that was severe enough to cause a coma was fatal in about 25 to 30% of cases, though other experts said the figure was closer to 15%.

"The problem with any acute brain injury is that the brain is a very delicate organ. The skull cannot expand, so when the brain swells, the pressure goes up, and it constricts its own blood supply. It cuts
the oxygen to the brain and worsens the damage, and that could potentially kill him," he said

Brain scans showed that Schumacher suffered bruising on both sides of his brain. Whether the damage is permanent, and how severe it may be, will be clear only once he has come out of coma and doctors can assess his condition more fully.

To induce hypothermia, doctors inject patients with saline solution chilled to 4C. The patients are covered with a cooling blanket to hold them at a few degrees below normal body temperature. The cooling lowers the brain's demand for oxygen, which in turn reduces the volume of blood flowing into the organ. Cooling may also reduce inflammation in the brain.

But the swelling may not reach its peak for a few days yet. If doctors cannot control the pressure by cooling alone, they may perform an operation called decompressive craniectomy, which removes a large section of bone from the front or side of the skull to relieve pressure on the brain. The procedure is controversial, though, and can cause patients more harm than good.

"The goal now is to control the brain pressure, that is the critical stage they are at," said Peter Hutchinson, a reader in neurotrauma at Cambridge University. Inducing hypothermia puts patients at greater risk of infections, especially chest infections, which intensive care staff will be watching for. The next 48 to 72 hours would be crucial for Schumacher's recovery, Hutchinson said.

When Schumacher's brain pressure returns to normal, doctors can start to warm him up again. This is done very slowly, at about 0.25C per hour, to avoid the brain swelling up again. Doctors can then stop administering the anaesthetic that is keeping him in a coma and wait to see if he comes round.

"When you stop the anaesthetic, you look for the time of emergence from the coma. It will be a gradual process of recovery. It can take hours for a minor injury, or it can take days or weeks," Hutchinson said. Patients who are still in a coma after six months are said to be in a persistent vegetative state.

The bruising on Schumacher's brain is similar to that seen in victims of road traffic accidents, when the head stops suddenly but the brain keeps moving inside the skull. The blow causes shearing forces that damage the brain tissue. If Schumacher survives, as many surgeons believe he will, his recovery depends on how serious these injuries are, and which parts of the brain are affected.

"When nerves get damaged or torn, the brain has very limited capacity to repair itself. So it depends where the lesions are and whether you have reserves. Some parts of the brain are less important than others," said Hutchinson.

"Everyone is trying to speculate about an outcome, but that is very difficult. The trouble with brain injuries is that they are all so different. The worry is, if you are going to survive, what is the quality of survival? The potential for disability may be severe," said Hutchinson.

Tony Belli, a consultant neurosurgeon and reader in neurotrauma at Birmingham University, said that Schumacher's age, fitness and psychological strength would help his recovery. "He's got a lot of factors in his favour. He's more likely than not to make a good recovery, despite all the concerns that have been raised. From the description of his injuries, it will take weeks, even months to recover, but I do expect him to make a good recovery."