Hypothermia and Brain Arrest Protocol
Nitin K Sethi, MD
Assistant Professor of Neurology
New York-Presbyterian Hospital
Weill Cornell Medical Center
New York, NY 10065
Recently I attended the American Academy of Neurology (AAN) annual meeting held in Seattle. One of the topics of interest was the use of hypothermia to improve the outcome of patients after cardiac arrest or traumatic brain injury. Since the neurological outcome of patients presenting after a cardiac arrest (whether in hospital or out in the field) is usually dismal, I thought this shall be a good topic for me to discuss here.
The brain needs oxygen to survive and does not do well if deprived of oxygen. Hypoxia (lack of oxygen) occurs after cardiac arrest (the circulation of blood to the brain is interrupted when the heart stops beating as occurs in a cardiac arrest). If the circulatory flow is not rapidly reinstituted (meaning the heart is not restarted) irreversible neuronal death ensures. The usual scenario is as follows. A patient suffers an out of hospital cardiac arrest. A call goes out to 911. The EMS team is on the scene shortly. The patient is noted to be either in cardiac arrest (we call this asytole) or the heart is beating but ineffectively and there is no palpable pulse (we call this ventricular fibrillation). The heart is revived by either injecting drugs or shocking (with the help of a hand held defibrillator) and there is return of palpable pulse. Alls well you might say but the story is far from over!!!
Even though the heart has been revived the brain has taken a hit. During the time when the heart had stopped, there was a lack of blood flow and oxygen to the brain and irreversible neuronal death has occured. So we have a patient whose heart is now beating but the brain is dead. This patient may never make a meaningful neurological recovery. Some of these pateints end up in persistent vegetative state (PVS) or minimally conscious state (MCS).
By the time, I as a neurologist am called to see the patient, there is precious little I can do. The brain is already dead!!! I can just prognosticate and tell the family that their loved one shall never have a meaningful neurological recovery. In other words, I help them in deciding when to pull the plug!!! Nothing makes me feel more helpless. I did not enter neurology to prognosticate, I entered neurology and medicine to save a life and heal.
So that is why hypothermia for cardiac arrest sounds so promising. Recent studies have shown that if the brain is cooled (there are different ways to cool the brain from using high tech cooling blankets and beds to more primitive but equally effective techniques like bags of ice) to 32-34 degree centigrade for 12-24 hours following cardiac arrest, neuronal death does not occur. Till the heart is revived, the brain remains viable!!!
This research has led to the institution of a Brain Arrest Protocol in some big academic centers. Once a patient who has suffered a cardiac arrest is received, hypothermia protocol is immediately instituted. This has resulted in improved survival rates in these critically ill patients. Patients not only survive but they survive with good neurological outcomes.
If the hypothermia is prolonged or if the temperature is lowered too low it can cause complications and increase the risk for sepsis and cardiac arrhythmia. Hence this protocol is at present still in its infancy but I have a feeling this shall become a standard of care very soon.