What’s an Induced Coma?

How to mend a swollen head.

On Monday, a teenager was sentenced to six months in prison for tossing a 20-pound turkey into oncoming traffic. The bird smashed the face of Victoria Ruvolo, who had to spend two weeks in an induced coma as a result of the attack. What’s an induced coma?

A therapy that reduces brain-swelling after a traumatic head injury. A blow to the head causes brain damage in two stages. First, the initial impact destroys some tissue. Then the brain starts to swell up, either because individual cells start to take on water or because blood begins seeping into the brain tissue. (Normally the “blood-brain barrier” prevents this from happening.) The swollen brain squeezes up against the inside of the skull, causing more tissue damage. It can also become so engorged—and its blood vessels so constricted—that it suffocates from a lack of oxygen.

Doctors can try to reduce swelling by putting the patient in a coma. (Among the other available options: opening a hole in the side of the head to let out fluid, cutting out portions of the inflamed brain, or inducing hypothermia.) Inducing a coma is beneficial because a comatose brain uses less energy—and oxygen—than an awake and alert one. A brain that’s been shut down in a coma can survive longer with a limited supply of oxygen. The coma also further reduces blood flow to the brain, which eases pressure in the cranium. Reduced blood flow does mean less oxygen gets to the brain, but since comatose brains don’t need much oxygen this isn’t a problem.

To induce a coma, an anesthesiologist typically infuses a patient with increasing doses of the barbiturate pentobarbital while monitoring her brain waves with electrodes. Once the brain shuts down, the patient won’t be able to breathe or eat on her own, so doctors must hook up life support systems for the duration of the coma. Someone might be left in this state for several days or several weeks, as doctors continue to infuse the drug. Doctors can monitor pressure in the skull with a special sensor. If and when the brain-swelling begins to subside, they can turn off the pentobarbital and gradually bring the patient out of the coma. Since the anesthetic lingers in the body for several days, “waking up” takes awhile.

Though induced comas have been used for decades, it’s not clear how well they work (and there are some risks). We know they can reduce the severity of swelling, but no study has ever shown that patients turn out better for having had the procedure. More recently, some clinicians have tried to induce comas in patients whose brain damage doesn’t come from a head injury. A girl in Wisconsin was put in a coma after contracting rabies, and just last week the heir to the Fiat automobile fortune awoke from an induced coma following a drug overdose.

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Explainer thanks David Warner of the Duke University Medical Center.