In reference to the recent unfortunate events regarding basketball player Lamar Odom, I have heard many inconsistent reports, from declarations that he is “brain dead” to reports that he woke up and spoke. This got me to thinking about how brain death, death, cardiac arrest, and altered levels of consciousness are often inaccurately portrayed in the media, and I wanted to clarify a few misconceptions
First of all, when someone is brain dead, they are, for all intents and purposes, dead. Death is defined as brain death and/or cardiopulmonary death. If Odom were brain dead, he could not wake up. If he really woke up, he was never brain dead. Brain death = legal and biological death. Brain death means that the person has no function in their cortex (upper brain, which produces consciousness) OR in their brainstem (the “rudimentary” brain, so to speak, which controls functions such as breathing). When someone is brain dead, their entire brain is permanently functionally damaged and can never return to a functioning state in any way.
The way that we as doctors assess for brain function is first by clinical exam. First, we make sure to minimize factors confounding the exam (for example, turning off medications, or warming someone who had been hypothermic).
If someone is awake, alert, and conscious, they are demonstrating that they have at least some cortical (upper brain) function. When someone has altered levels of consciousness (for example, they are somnolent) The exam then aims to answer “how good is their cortical function?” — can they speak? Can they interact or express themselves in some way? Can they visually track? Can they follow simple commands?
People who are unconscious can sometimes have spontaneous movements (such as abnormal posturing), but they will not have purposeful movements or meaningful interaction with their surroundings.
When someone is unconscious, we want to see if they have some “lower brain,” or brainstem function. We start by examining cranial nerve reflexes. Cranial nerves are peripheral nerves that have their roots in the brainstem, and they control head and neck functions such as facial expressions, facial sensation, and pupil dilation and constriction. Reflexes mediated by cranial nerves include pupil constriction upon stimulation with light, blinking upon touching the cornea, and gagging when the back of the throat is stimulated (such as with a q-tip). Someone without brainstem function (i.e. a brain dead person, or equivalently a dead person) has fixed dilated pupils, will not react to stimulation of their corneas or throat, and cannot breath on their own, as the brainstem controls the respiratory drive.
What does it mean to “pull the plug” or remove “life support” from a brain dead person? Often, brain death is declared on a person who is intubated and on a ventilator—they have a tube (an endotracheal tube, named because of its position within the trachea) down their throats, and this tube is connected to a machine called a ventilator that moves air in and out of the lungs using positive pressure. The drive to breathe is located in the brainstem, so a brain dead person will not breathe on their own if the breathing tube is removed (if they are extubated). Once they experience respiratory arrest, their heart will soon stop beating and pumping because it is not being supplied with oxygen (the heart’s drive to beat is actually independent of the brain, but without oxygen the cardiac muscle will stop functioning). So, someone who has experience brain death will, inevitably, if left untouched by medical devices, swiftly experience cardiopulmonary death.
Keeping a brain dead person on a ventilator is not “keeping someone alive”—it is oxygenating and perfusing a corpse. The medically appropriate next step after someone is declared brain dead is to extubate them within a reasonable amount of time (eg. sometimes a few hours to a day, to give the family time to process). There are situations, however, where a person is NOT brain dead, but they are breathing with the help of a ventilator. Sometimes, based on the patient’s prior wishes, his or her durable power of attorney (often a spouse, a parent, an adult child) makes the decision to extubate them and let nature take its course.
Why does the heart keep pumping if the brain is dead? That is because the heart beats independently of the brain. The heart has its own pacemaker, and the heart will continue to function (if it is a viable organ) for as long as it continues to receive oxygen. A viable heart removed from the body would continue to pump if it received adequate tissue oxygenation. When a person dies naturally (i.e., when they are not intubated and on a ventilator), however, both brain death and cardiopulmonary death occur (the heart stops once breathing stops, and breathing stops once the brain dies. Sometimes, the heart dies first, and then the brain dies because it is not getting oxygenated blood flow).
Cardiac arrest occurs when your heart suddenly stops. Cardiac arrest is not the same as a “heart attack,” or myocardial infarction, which is when a coronary artery (vessel that brings oxygenated blood to the heart) gets blocked, such as by a clot that gets stuck in a plaque (plaques often form on vessels, narrowing of the vessel). A heart attack COULD lead to cardiac arrest, but there are several other events that can also cause a cardiac arrest. Also, the majority of heart attacks do not cause cardiac arrest.
Sometimes, however, a person can have serious brain damage and can be in a coma for days, but can still have brain function and a chance for some sort of meaningful recovery. I recently saw two patients around the same time who had experienced cardiac arrests. One died, and one is alive and interactive. Both received CPR at the scene, and both were brought to the hospital and their bodies were cooled (therapeutic hypothermia). Both were intubated and on ventilators, and unresponsive for several days. Bill had his eyes open, was at first not visually tracking, but was withdrawing to pain, and was moving his arms on the bed spontaneously. Tim was completely unawake, with eyes closed, not moving, not responding to pain; however, he did have cranial nerve reflexes. We did a test called somatosensory evoked potentials (SSEPs), which showed that Bill had some cortical activity, while Tim had only brainstem function. Neither was brain dead, but Tim had a very poor prognosis based on clinical exam and SSEP; Bill’s prognosis was at that point unclear. After a few days, however, Bill started tracking our faces with his eyes. He started following simple commands (at first, he would blink and shut his eyes on command. Next, he would squeeze hands on command. Then he became able to give a thumbs up, lift his legs). Soon Bill passed spontaneous breathing trials and he was extubated. He was very disoriented, not knowing where he was or what year it was, but he could verbalize, and he could tell me his name, his wife’s name, his hometown. Day after day, he continued to get better. He still has serious neurologic deficits, but he is awake and alive. Tim, on the other hand, did not get better. Each day, he looked the same as the day before. His family decided to extubate him, and he eventually passed.
Cardiac arrest is a serious event, and most who experience it die. However, like my patient Bill, there are some who do survive. However, most who survive a cardiac arrest are left with serious permanent neurologic deficits. Only a very small fraction, however, return to their baseline functioning. Someone might return to baseline–for example, if he or she were were young and healthy at baseline and received effective CPR right away.