Thursday, July 3, 2008

Death and the brain

Today I'm going to post about death.

This post is dedicated to my canine buddy whom I knew for thirteen years, Hot Shot (don't laugh; I got the dog when I was seven, and I called him that for thirteen years - I'm 20, and I got him when he was a mere sixteen weeks old - he died at the ripe old age of thirteen, which, if you use the 7 years to one human year rule, is equivalent to a 91-year-old human. He was an elderly ), who I euthanized two days ago after finding he suffered from a tumor on his enlarged heart, a tumor on his testicles, chronic kidney failure , and a stroke. He was beginning to convulse as I held his furry little body while the veterinarian sedated him, and the only indication that he'd died was his stopped heart, his lack of breathing, and some spasms. He died peacefully, and I'm glad he has no more agony, even if he is no longer alive. I feel like shit, as you can guess, and even though I look mildly stoic on the outside, I am grieving for my old very small friend who is, at least, going to do his part for nature after he has croaked by feeding organisms. Eat up, bacteria.

When the brain dies, all electrical activity ceases. Simple.

The problem is, how do you determine the brain has died? The American Academy of Neurologists has a set of criteria for determining brain death.

Brain death is defined by the American Academy of Neurologists as 'the irreversible loss of function of the brain, including the brainstem'. The brainstem is an important part of the definition because it controls your basic bodily functions - breathing and heartbeat.

The criteria are listed thus:

- Directly quoted from the list of criteria, clinical or neuroimaging evidence of an acute CNS catastrophe (which is our term for a critical occurrence in the brain or spinal cord) that is compatible with the clinical diagnosis of brain death
- Exclusion of complicating medical conditions that may lead to a different assessment - rule out various disturbances in the body's chemical milieu
- No poisoning
- Core temperature higher than 90 degrees F (32 degrees C)
- Three cardinal findings: coma/unresponsiveness, absence of brainstem reflexes, and apnea
- Eyes: Unresponsive to bright light, normal to dilated, no oculocephalic reflex if there is no apparent fracture or instability of the cervical spine, no deviation of the eyes in response to ear irrigation
- Facial sensation and motor responses: No corneal reflex, no jaw reflex, no grimacing in response to pressure on sensitive parts of the body
- Pharyngeal reflexes: no response to stimulation with tongue depressor, no cough response to bronchial suctioning
- PCO2 pressure higher than 60 mm Hg

Visual observations that can still be seen in brain death include spontaneous movements of limbs other than pathologic flexion or extension response, respiratory-like movements, sweating, blushing, tachycardia, normal blood pressure without pharmacologic support or sudden increases in blood pressure, absence of diabetes insipidus, deep tendon reflexes, superficial abdominal reflexes, triple flexion response, and the Babinski reflex (quoted almost directly from the criteria).

Tests that can be performed to diagnose brain death include conventional angiography, EEG, transcranial Doppler ultrasonography (except in ten percent of patients, who may not have temporal insonation windows, which are structures in the temporal bone of the cranium allowing sound waves to provide a picture of your brain), small systolic peaks in early systole without diastolic flow or reverberating flow, technetium-99m hexamethylpropyleneamineoxime brain scan, and somatosensory evoked potentials.

These criteria are vital in determining when a patient has died so the family may take them off life support, harvest their organs for donation, and a physician may declare them legally dead. There have been people declared legally dead who are still alive. There is a bunch of hemming and hawing about when death occurs, mostly split along religious/ideological lines (as an atheist, I think when their brain goes, they're effectively dead). Even among physicians, there are variations. - according to 'Greer et al. (2008) Variability of brain death determination guidelines in leading US neurologic institutions. Neurology; 70: 284-289', there is significant variability in 'requirements for performance of the evaluation, prerequisites prior to testing, specifics of the brainstem examination and apnea testing, and what types of ancillary tests could be performed, including what pitfalls or limitations might exist'. Does brain death stop, for that matter, when consciousness stops? Consciousness comes from our frontal lobe; we would have to find a way to judge when those neurons fall silent. (But that gets into a big argument about what consciousness is, and philosophy of mind is, as you know, one of the things I love to hate, as a person in neuroscience who is highly positivist, highly materialist, and absolutely hates dualists. Why the hell are they still debating whether the mind is part of the brain when we've already established it and are doing more research? Let us people in neuroscience do research on the brain; you go sit over there with your Kant, especially you bloody dualist bastards, who can keep your Descartes, the worthless frog)

If the diagnosis of brain death is this shaky, a few limitations might exist in determining it: misinterpretation of tests, unreliable test results, complicating comorbid symptoms, unknown factors in the neurological milieu (likely neurochemical processes), and other bits of human imperception.

I expect, as we grow in our knowledge of the healthy living brain, that we can use it to determine when that brain stops being living.

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