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Why induced comas help injured brains

By Elizabeth Landau, CNN
December 31, 2013 -- Updated 1139 GMT (1939 HKT)
  • Doctors sedate patients to try to reduce the energy requirements of the brain
  • Therapeutic hypothermia is used to try to reduce swelling
  • Traumatic brain injuries can release cascade of chemicals toxic to the brain

(CNN) -- Formula 1 driver Michael Schumacher suffered severe head trauma in a skiing accident and arrived at a French hospital in a coma.

To promote healing after Sunday's accident, doctors are keeping the German driver in a medically induced coma and lowered his body temperature, said Dr. Jean-Francois Payen, chief anesthesiologist at University Hospital Center of Grenoble, France, where the driver is being treated.

Traumatic brain injury causes the brain to swell, just like the inflammation that happens when you injure an elbow or knee. But because the brain is trapped inside your skull, pressure on the brain increases and restricts a lot of critical functions, such as blood supply, said Dr. David Wright, director of emergency neurosciences in the Department of Emergency Medicine at the Emory University School of Medicine.

"You're worried because the skull is a closed space," said Dr. Nicholas Schiff, professor of neurology and neuroscience at Weill Cornell Medical College. "As the brain starts to expand, the only place it has to go is down and out, and you damage the brain stem. You can die. You can create a lot of tissue damage."

Formula 1's Michael Schumacher in critical condition after skiing accident

Doctors take steps to try to reduce the energy requirements of the brain, which in turn reduces blood flow and pressure, and allows the brain to rest.

"It's kind of like cooling the engine down and allowing the healing process to, sort of, slowly occur," Wright said. "It also decreases the swelling of the brain, hopefully, and reduces the chance that you're going to get that increased intracranial pressure that's occurring."

The anesthetic propofol is commonly used for induced coma, although doctors have not made public what medications are being used in Schumacher's case.

Schumacher's specific injuries and the type of surgery he underwent at the hospital have not been disclosed, so Wright and Schiff could not comment on his individual case.

Schumacher in coma after brain injury
What happened in Schumacher accident?
Schumacher in 'critical' condition

Head injuries are classified as mild, moderate or severe, according to how people interact with their environment. In mild injuries, patients are awake, alert and following commands. Moderate injuries might leave a patient confused or combative and not following commands. A patient with severe injury is in a coma.

When the head is hit hard, the brain moves back and forth within the skull, causing further stretching injury and damage, Wright said.

A secondary "cascade" of events can cause further harm by releasing chemicals that are toxic to the brain. Ions such as calcium flood into the brain's cells, which can cause cell death. This process causes swelling. If a cell doesn't die immediately, it may be injured enough that it essentially kills itself, a phenomenon called apoptosis.

"The goal in management is to really try to reduce and slow any of those processes down so you can save as many of the brain cells as possible," Wright said.

Schumacher's body temperature is being kept at between 34 and 35 degrees Celsius (93.2 and 95 degrees Fahrenheit), and he is being given anesthetics. This is called therapeutic hypothermia; too much colder than that temperature range would be harmful, Wright said.

The treatment of lowering body temperature is generally effective at keeping down intracranial pressure, but the evidence is not clear about the therapy improving outcomes in the end, Wright said. It also lowers the energy required by the brain and slows the swelling.

The biggest part of the brain's inflammatory response to injury peaks after 48 to 72 hours, so doctors usually keep the body cool for up to three to five days, Wright said.

CNN's Caleb Hellerman contributed to this report.

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