Apr 08 2008

Brain Dead

It is often said of Paris Hilton that she is famous for being famous. Well, Zack Dunlap might have her beat – he is famous for not being dead.

In November 2007 Zack Dunlap was involved in a serious 4-wheel off-road biking accident, a roll-over resulting in severe head injury. He was flown to a nearby hospital where he was treated by trauma surgeons. His condition was critical. At 36 hours after his accident the doctors taking care of Zack feared that he might be brain dead. As Zack was a registered organ donor, they wanted to perform a confirmatory test so that if brain death were confirmed, the process of organ donation could begin.

A PET scan was performed at 36 hours. PET scanning (technically referred to as Technetium-99m hexamethylpropyleneamineoxime brain scan) is a measure of blood flow to the brain. Zack’s doctor, Leo Mercer, showed his parents the scan – his brain was entirely black. No blood flow. This was sufficient to meet criteria for brain death. The process of organ donation began.

About four hours later, while the family was saying their goodbye’s, Zack moved his foot in response to his cousin rubbing a knife blade along his foot. His responsiveness was confirmed by squeezing his nail-bed – he moved his arm with clear purpose. The diagnosis of brain death was set aside, and the process of organ donation was stopped, Zack was returned to full care and he slowly recovered. Zack’s story came up in the news again recently following a TV interview in which he said that he was doing OK.

The story has prompted many questions, and the mainstream media reporting has been ill-equipped to deal with them. How could someone be declared brain dead when they are not really dead? Was his recovery a miracle, a medical mystery, or a simple mistake? Reader responses tend to fall into three categories: those declaring the event a miracle, those worried about the entire notion of brain-death, and those putting the whole thing down to a medical error. Here is a typical comment encompassing the first two themes:

This is truly a blessing from GOD We should always put God first. It really bothers me now, how many people have been pronounced dead and harvest the parts and were really alive. I am a donor myself but I hope with God on my side if and when I am pronounced dead they don’t do that to me. How do you actually know if they are really deceased? I wonder how many other people who have donated their loved ones organs are asking the same question.

There is no need to invoke either a miracle or medical mystery in this case. The simplest explanation is that the PET scan was either in error, or was reflecting a reversible situation. There is much to suggest this in this case, but first let me give some background on brain death.

The concept of brain death developed for those situations in which a person’s body is still viable – their heart is still pumping and their organs work – but their brain is damaged beyond recovery. This is a common situation in the modern world of auto-accidents. Also, the need for organ donation creates the need to be able to declare someone dead before their heart and lungs give out. Brain death is a legal definition, and in the US is determined state by state. However, there are published medical guidelines, and most states follow the guidelines. The American Academy of Neurology published guidelines on brain death are authoritative.

As a practicing neurologist I have conducted numerous brain death exams. The criteria are very strict – there has to be no evidence of any brain activity, including any primitive or automatic brainstem activity. (Nerve reflexes mediated outside the brain do not count against brain death.) A specific and detailed exam is required – above and beyond the routine neurological exam. For example, it must include an apnea test in which all respiratory support is turned off in order to generate a maximum safe respiratory drive and still result in no spontaneous respirations (breathing is mediated in the brainstem). The slightest twitch of brain activity rules out brain death. In addition, it is recommended that the exam is repeated after at least 6 hours (in CT we use 24 hours) to make sure the clinical brain death is persistent. Finally, there cannot be anything reversible that can suppress brain function, like drugs or hypothermia.

Confirmation with certain laboratory tests is optional but useful in some cases. From most to least sensitive, the tests that are used include an angiogram to look for blood flow to the brain, and EEG (electroencephalogram) looking for any brain electrical activity, doppler test for blood flow, a PET scan for metabolic activity, and a somatosensory evoked potential looking for brain responsiveness.

Let’s take a look at this case. I only have the details provided by the media (I have called Dr. Mercer but have not gotten through yet), so I can comment on some things and not others. The primary problem I have with this case is that the determination of brain death was made 36 hours following a severe head trauma. Brain trauma causes edema or tissue swelling, just like would happen to any body part after injury. This brain edema increases over about 72 hours and then starts to resolve. Because the skull is a closed space, this swelling squeezes the brain causing temporary dysfunction. It can also cause permanent damage in some cases. But during this period any clinical assessment of the patient in order to determine the amount of permanent brain damage is problematic because you can’t know how much is due to reversible swelling. Patients may look terrible, but then in a few days when the swelling goes down make a remarkable recovery. This is more likely in younger patients because young brains are plump and therefore they swell more and there is less room in the skull to begin with.

In fact when I consult on such cases I also couch my opinions in terms of – we cannot make any definitive statements during this period, we have to wait until the swelling resolves. You can infer how much damage is likely based upon laboratory tests, like a CT scan or MRI which can show the edema and may also show if there is large amounts of blood in the brain or other anatomically visible abnormalities.

In short (with the caveat that I do not have all the facts from a first hand source) I have a problem in general with declaring a young person brain dead 36 hours after a head trauma. Unless there were solid laboratory evidence of irreversible brain death I would always wait at least until the swelling resolves to make this diagnosis.

In this case it appears that is what the team did – they ordered a PET scan. It is possible, even probable, that there were other tests not mentioned in any of the news reports. An EEG would be routine, for example. Relying on just a PET scan is problematic. It is down the list in terms of sensitivity and is not typically the only test used for confirmation of brain death. There is evidence that it can show brain death, but I could not find any studies that measure the probability of a false positive – meaning that the test falsely confirms brain death, as appears to be the case here. In addition, there are some technical aspects of using a PET scan in this manner that create the possibility of error. For example, if the radioactive label is not prepared or injected properly that can result in no signal – which would then be falsely interpreted as no brain activity (this is my guess as the most likely case here). You can scan the liver just to make sure you are seeing some signal and therefore to validate the test. That is one of those details not reported in the mainstream media and I would love to get from the doctor or records in this case.

To summarize – in this case the clinical determination of brain death was made too early to be definitive. The only confirmatory test that was mentioned, the PET scan, is subject to technical errors that could have erroneously resulted in the absence of any signal. In this type of case (especially considering the age of the person) my personal recommendation would have been to either wait a couple of days after the edema mostly resolved, or to do more definitive confirmatory tests, like an angiogram for cerebral blood flow. I suspect that the patient was not thoroughly examined because the doctors were relying upon the PET scan, which was very likely in error. (Relying upon a false test always causes problems.)

It should also be noted that this case is a rare anomaly. The criteria for brain death are very conservative, and if properly employed there is almost no chance (I am tempted not even to say “almost”) of error or of meaningful recovery following a diagnosis of brain death.

But now this case will live on in the public consciousness. Public opinion is likely to be disproportionately affected by this anomalous case rather than the thousands of cases that do not warrant reporting.

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