Coma/Brain Death
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- Define coma.
- An unarousable state where the patient is completely unresponsive to deep noxious stimuli and shows no sign of interaction with his/her environment.
- What neural structures are neccessary for the maintenance of consciousness?
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1. Cerebral Hemisphere
2. brainstem (Ascending recticular activating system)
3. connecting fibers of both structures - Structurally, what aspect of the brain is depressed in coma?
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1. Both cerebral hemispheres
2. ARAS at the level of the midbrain/diencephalon/pons
...due to either a structural, metabolic lesion or psychogenic causes. - What are the three common processes leading to coma?
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1. Supratentorial mass lesions
2. Subtentorial mass lesions (posterior fossa)
3. metabolic disturbances-responsible for 2/3 of coma (anoxia, ischemia, hemorrhage, toxins) often reversible. - What five physiological variables are essential for the localization of mass lesions in coma?
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1. state of consciousness
2. breathing pattern
3. pupillary reactivity
4. eye movements (oculovestibular activity)
5. motor response - Discuss uncal herniation and its clinical presentation.
- hemispheric mass lesion unilaterally compressing the edge of the uncus through the tentorial notch manifesting as initial III nerve palsy...or a unilateral dilated (blown) pupil.
- Discuss central herniation and its clinical presentation.
- Conus pressure transmitted to diencephalon and eventually brainstem resulting in progressive decrease of consciousness, and bilateral pupillary dilitation.
- What clinical evaluation is vital to determination of the etiology of coma?
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1. History
2. ABC's (airway, breathing, circulation)
3. Blood Glc, CBC drug toxicity panel. - What is the definition of "death?"
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1. cessation of cardiac/respiratory function
2. Irreversible destruction of neuronal contents of the intracranial compartment resulting in loss of BOTH cortical and brain stem activity. - Define Brain death?
- Absence of clinical brain function when cause is known and determined to be irreversible.
- What are the prerequisites for "clinical" Dx of brain death?
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1. Clinical/neuroimaging evidence of acute CNS injury.
2. Exclusion of complicating confounding conditions (electrolyte imbalance)
3. absence of drug intoxication/poisoning
4. core body temp > 32 degrees celsius - What are the three cardinal reflexes associated with brain death?
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1. Coma/unresposiveness- lack of response to deep noxious stimuli (sternal rub)
2. Absent brainstem reflex- unreactive pupils, absence of occulocephalics (cold calorics), occulovestibular reflexes (dolls eyes), gag and cough
3. Apnea- absence of respiratory movments and arterial pCO2 > 55mmHg after 5-8 min. of passive delivery of 1000% oxygen. - List reflexive manifestations occasionally seen and commonly mis-interpreted as evidence for brainstem funciton?
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1. Spontaneous movt of extremities
2. respiratory-like movt
3. sweating, blushing, tacchycardia
4. normal bp
5. presence of deep tendon reflexes
6. Babinski reflex - Discuss structural vs. metabolic lesions.
- Structural lesions include strokes, tumors, hemorrhage & trauma, hyrdrocephalus, infection. Whereas metabolic lesions can be temp disorders, thiamine/b12 def, electrolyte/base disturbance, diabetic ketoacidosis.
- What are the two top causes of supratentorial mass lesions?
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1. Subdural hematomas
2. Intracerebral hemorrhage - What is emergency treatment for comatose patient?
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1. Thiamine (alcoholic, B12 def)
2. Dextrose (hypoglyemia)
3. Naloxone or Narcan for opiod OD
4. Flumazenil- for benzodiazepene OD - Why is thiamine administered before glucose in emergent situations?
- Thiamine is a cofactor in Glc metabolism, glucose will precipitate all thiamine and intesify the thiamine deficiency.
- What is the Glasgow Coma Scale (GCS)?
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three point scale utilized to assess level of consciousness. (eye, response, motor response, verbal response)
15 normal
Comatose if <8
True coma is 3 - ***Characterize the locale of the lesion in a patient looking away from the side of the weakness.
- Hemispheric lesion (RMCA stroke weakness in the left field thus eyes gaze to right side)
- ***What eye movt are characteristic of brainstem stroke?
- Weakness in left field eyes gaze towards same side as weakness....thus pt looking to the left.
- List your differential for a comatose patient with pinpoint amd reactive pupils?
- 1. Pontine coma, Metabolic Coma & Opiod Overdose
- What is the oculocephalic reflex? What are dolls eyes?
- Movt of eyes in direction with fast head movement. Dolls eyes are a manifestation of intact brainstem functionality- eyes lag slightly behind directional/rotational movement of head so that it appears that they oppose head movement. Dolls eyes are a function of the brainstem ONLY IF HEMISPHERES are not working.
- What is the oculovestibular reflex?
- COWS (cold opposite warm same) for a person awake and alert/
- Name the loci of the neural generator for the fast/slow component of nystagmus.
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Fast component is mediated by the hemispheres
Slow component is mediated by the brainstem - What is your prediction for the outcome of Left eart cold water calorics vs. eye movt in comatose patient with intact brainstem?
- Eyes drift to left due to absence of hemispheric input.
- Discuss decorticate posturing and its clinical implication.
- Arms flex and legs extend in response to sternal rub (noxious stimuli) indicatiev of a lesion above the red nucleus...intact brainstem
- Discuss decerebrate posturing and its clinical implications.
- Extension of legs and arms in response to noxious stimuli. Ominous finding that little brain function is left.
- What type of breathing pattern is typically a sign of impending herniation?
- Cluster breathing
- What type of breathing would be characteristic of a patient suffering a leison in the lower pons?
- apneustic breathing...taking a deep breath, hold and release. Square wave breathing
- What type of breathing is characteristic of a person suffering from a lesion in the diencephalon?
- Cheyenne-Stokes- crescendo/decrescendo breathing pattern
- What clinical manifestations are characteristic of pschogenic coma (psuedocoma)?
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1. Often reversible with pain...patients resistant to noxious stimuli
2. Saccadic eye movements-strip of paper with stripes will induce nystagmus if not comatose
3. Drop arm towards face and hand will never hit face - What reflexive activities are typically exhibited by patients in a persistent vegitative state after 2-4weeks?
- Return of diurnal rhythm, chewing, yawning...etc.
- True/False. Decorticate and decerebrate posturing are frequently observed in brain dead patients.
- False. Both forms of posturing are indicative of brainstem functionality.
- What clinical work-up is necessary for the declaration of brain death?
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Two neurological exams...the second usually 2-6 hours after the initial exam and the apnea test (pCO2>55).
**Confirmatory/ancillary tests are not neccessary