When is a person really dead?

[E.S.Prakash]

From B Praveetha, Year 1 Student

Last month I watched in Discovery Channel; in Germany a lady whose heartbeat had stopped was brought alive. A man who had drowned in sea for few days was also brought alive. The doctor said that the drowned man was saved because his tissues weren't damaged. Is it possible to bring people alive even after few days have passed since their heartbeat has stopped? Can the brain survive without blood supply and sufficient nutrients for that long?

[E.S.Prakash]

Based on whatever we did in Forensic Medicine:

Death is defined as the irreversible cessation of life. We have something called somatic death (loss of sensibility and movement, cessation of cardiovascular, respiratory and central nervous function) and cellular death (ultimate destruction of cellular elements).

Death is a big problem in medical science because it has to be differentiated from what is known as apparent death or suspended animation (where the tissues metabolize on minimal dissolved nutrients and oxygen). Suspended animation is possible in the cases like drowning, heat stroke, anesthesia, yogic practices etc. and individuals in suspended animation can be revived with cardiac massage, defibrillation, stimulation etc.

Hence we use the terms brain death, brain stem death and cortical deaths to define the exact moment of death which proves with better objectivity. They are defined based on certain criteria with tests on the presence or loss of brainstem reflexes like corneal, oculocephalic, oculovestibular, pain, pupillary light, gag, cough reflexes apnea test and the presence of an irreversible coma. They are also ancillary tests which measure blood flow to the brain and electrical activity up there. It is interesting to note that these tests do not include the presence of a heartbeat as they perceive a person is only as alive as his neurons are. So a person is really as alive or as dead as his neurons
are.

Responding to this question, an irreversible coma can only be diagnosed if we rule out certain factors which make the coma reversible like hypothermia (seen in drowning) where the body has to be warmed up to normal temperature before any decision is made.

However these tests are not without fallacy and suspended animation is often missed hence death has to be certified by (if I am not mistaken) by two doctors conducting these tests at certain intervals made specific for different age groups.

Hope this helps for this discussion.

Ravivarma Panirselvam
Year 4 Student
*****************************

[Nicholas Cheong]

Dear Praveetha,

Is that episode you are alluding to available anywhere on the internet?

A person is said to be dead if he is brain-dead.  The causes of brain death (though multiple and variable) all culminate in the brain losing its oxygen supply. With time, the brain necroses, losing all its functional units (neurons).  A diagnosis of brain death is made using factors including fixed and dilated pupils, lack of eye movement, and loss of respiratory reflexes. Brain death is a legal indicator of death. There is also something called the clinical death. I don't know much about it though.

Theoretically, the brain is not viable if cerebral blood flow is interrupted for more than 4 minutes. This is because irreversible ischemia sets in and subsequently necrosis.

Thank you

Nicholas Cheong
MBBS Batch 14

[E.S.Prakash]

Thank you Ravivarma  & Nicholas for your explanations.

I found on the net a few cases in which doctor had declared a person as brain dead and yet helped them out providing them life support

http://www.dailymail.co.uk/health/article-358065/Brain-dead-woman-gives-birth.html

http://www.cross-x.com/vb/showthread.php?t=963739

http://www.guardian.co.uk/society/2009/jan/13/ice-skater-soliman-birth

How this can happen? What is the mechanism behind these miracles?

B Praveetha
Year 1 Student

[E.S.Prakash]

Praveetha:

I'd suggest reading this NEJM article on Diagnosis of Brain Death http://www.ctdn.org/downloads/TheDiagnosisofBrainDeath.pdf

Brain Death in Children http://emedicine.medscape.com/article/1177999-overview

Brain Death needs to be distinguished from conditions that resemble it including severe brain damage;

Circulation and ventilation in "brain dead" individuals may be maintained for a considerable length of time with the health care technology available today - mechanical ventilators and circulatory support.

In the story you seem to quote (link below), the mother who had been 'brain dead' was maintained on life support with mechanical ventilators and appropriate circulatory support, so that the baby she was pregnant with could mature enough to the point that the baby could be delivered. See http://www.washingtonpost.com/wp-dyn/content/article/2005/08/03/AR2005080300224.html

You should also probably like to read this Case Report http://onlinelibrary.wiley.com/doi/10.1111/j.1471-0528.2005.00801.x/full#t1

ESP
*********************

[E.S.Prakash]

Let's review the basics:

The heart and lungs are dependent on the vasomotor centre and the respiratory centre respectively for their functions and if these 'centres' are damaged or destroyed by mechanical or metabolic causes, you can not
'bring life back' to that physical body. If there is a cardiac arrest due to an intrinsic cardiac, respiratory or metabolic disorder, and if resuscitation is started before irreversible neuronal injury occurs in the brain, and if the cardiac arrest is managed by a team of experts in a hospital-setting, it is well nigh possible to 'bring life back' to the physical body.

Now, the question is whether the brain will survive for a longer time in case of cardiac arrest. We know that cerebral neurons are very much susceptible to ischaemia. As Nicholas has pointed out, irreversible
neuronal injury can occur if neurons are hypoxic for three minutes continuously. Why are these neuronal cells so susceptible to ischemia, whereas some other cells in the body can survive for 6-12 hours?
Neurons have a very high metabolic rate; i.e., they have a very high demand for oxygen. If the metabolism of cerebral neurons (cerebral metabolic rate for oxygen is reduced, we can prolong the life of these cells. There are atleast 2 methods to decrease the cerebral metabolic rate (CMR). One is by inducing hypothermia. Profound hypothermia is extremely cerebroprotective because it will decrease CMR to almost zero (a flat EEG!). So, when the neurons do not have any activity, their life is prolonged just like the
other cells. And this is used post-cardiac arrest in a controlled environment to protect the brain after successful resuscitation. This is also used during anaesthesia for open heart surgeries, where the heart is
stopped and the perfusion is maintained by a cardiac bypass pump (the heart-lung machine). But profound hypothermia has deleterious effects when given for a longer periods and thats why it is given in a controlled
environment for short periods. This can occur naturally during drowning! Another way of decreasing CMR is by using cerebro protective drugs like thiopentone sodium. This will bring down the EEG activity but will not make the EEG a flat line! Infusions of thiopentone and propofol are used by anaesthetists and intensivists in the ICUs for cerebral protection in patients with head injury. So, if after a cardiac arrest and with no damage to the brain, if there are some factors causing natural or artificial reduction in the CMR, neurons will survive for a longer period of time.

I hope I have answered the query that was raised originally. If you have any uncleared doubts, pass them on.

Regards,

Dr. Prabhakar