Coma and Brain Death

Question 1

Define coma

Answer 1

sleep-like, unarousable, unresponsive state

-obtunded/stuporous are pts with impaired consciousness but some limited degree of responding

Question 2

What is clinically testable in coma?

Answer 2

only BRAIN STEM REFLEXES since cortical function is absent

Question 3

persistent vegetative state-whats going on?

Answer 3

• eyes periodically open or move
• sleep and wake cycle occur
• pain responsiveness may return, but meaningful interaction remains absent since severe cortical impairment persists

Question 4

what can cause coma

Answer 4

severe metabolic or systemic conditions that diffusely depress cortical function

Question 5

what can directly impair neuronal function

Answer 5

• hypoxia
• inadequate cerebral blood flow
• hypoglycemia
• drug intoxication or overdose

Question 6

what can indirectly affect cerebral cortex

Answer 6

• systemic infection
• metabolic disturbances
• hepatic or renal failure

Question 7

what in particular can cause permanent cortical deficits

Answer 7

the hypo’s:

• severe hypotension
• hypoxia
• hypoglycemia

Question 8

relationship between solitary cerebral lesions and coma

Answer 8

a solitary unilateral cerebral lesions doesn’t produce coma UNLESS it adversely affects the opposite hemisphere via brain edema or herniation

Question 9

what is the ship between coma and reticular formation

Answer 9

coma may be produced by a brainstem lesion if it disrupts the reticular formation
(the tegmental brain stem reticular formation, projecting to thalamic and subcortical nuclei, is important for wakefulness and arousal)

Question 10

what is the use of serial repeated observations?

Answer 10

may show progressive loss of neurological function and BS reflexes, often indicative of a rostral to caudal deterioration d.t edema or inflammation

Question 11

limited examination in an unresponsive pt

Answer 11

1. evaluation of motor responses
2. breathing patterns
3. pupil size and reactivity
4. reflexive ocular movements

Question 12

symmetrical vs asymmetrical abnormalities

Answer 12

• asymmetrical neurological signs strongly suggest a structural lesions (such as ischemic infarction, hemorrhage, or tumor)
• symmetrical abnormalities usually are due to a more diffuse or toxi-metabolic process (ie anoxia)

Question 13

do motor responses occur in coma?

Answer 13

no. motor responses to command or withdrawal to painful stimuli do not occur in coma.
- an appropriate localizing response to a noxious stimulus requires some cortical function

Question 14

Posturing (two types)

Answer 14

1. decorticate=flexion of upper limbs with extension of lower limbs; associated with a lesions at the level of the cerebral cortex or hemisphere
2. decerebrate=extension of the upper and lower limbs; associated with a lesions at the level of the midbrain (red nucleus)

Question 15

abnormal breathing patterns in a coma

Answer 15

-Cheyne-Stokes respiration-alternating tachypnea and apnea (crescendo-decrescendo respiration)
….can also be seen in CHF and health elderly

Question 16

How is Cheyne-Stokes respiration produced in a ca comatose pt?

Answer 16

• b/l cortical involvement d/t:
• -metabolic encephalopathy (ie renal failure)
• -unilat lesions with severe brain edema
• -b/l structural lesions in cerebral cortex

Question 17

central neurogenic hyperventilation

Answer 17

-rarely ma result from a lesion or edema in the low midbrain to upper pons

Question 18

ataxic respiration pattern

Answer 18

• consists of variable breaths at an irregular rate from a lesion or edema in the medulla, involving cardiorespiratory control centers there
• ominous for intubation

Question 19

pupillary light reflex in unconscious pt

Answer 19

• important!!

- in coma f/m metabolic causes pupillary light reflex is preserved

Question 20

sympathetic vs. parasympathetic fibers

Answer 20

• sympathetic (pupilloDILATOR) fibers travel down entire brainstem
• PS (pupilloCONSTRICTOR, CN3) fibers are a circuit at the midbrain level

Question 21

tectal (dorsal) midbrain lesion

Answer 21

-selectively involves the PS fibers=LARGE FIXED pupils (unopposed sympathetic)

Question 22

uncal herniation (neurologic emergency!)

Answer 22

-larger, BLOWN, fixed pupil unresponsive consensually or directly to light d/t compression of ipso CN3 f/m swollen temporal lobe

Question 23

pontine lesion

Answer 23

• selectively involves the sympathetic fibers=SMALL PINPOINT pupils (unopposed PS fibers)
• sans pontine lesion…same pupils d/t high doses of narcotics or cholinergic eyedrops used to treat glaucoma

Question 24

Reflexive eye movements

Answer 24

• important to check in every unresponsive pt

- may be suppressed by vestibulotoxic drugs (such as BZ) in absence of BS lesion

Question 25

oculocephalic reflex aka “doll’s eye reflex”

Answer 25

-normally: eye should move in the direction OPPOSITE to the lateral turn of the head by the examiner

Question 26

oculovestibular (cold caloric) reflex

Answer 26

• first: exclude ear canal blockage or ruptured TM

- nml: eyes move slowly toward cold (irrigated ear)

Question 27

emergency tx of comatose pt

Answer 27

-ABCs
-rule out hypoglycemia or empirically give 50% dextrose iv
(hypoxia and hypoglycemia cause neuronal death is not promptly corrected)

Question 28

structural causes of coma

Answer 28

=hemorrhage, ischemic infarction, mass lesion

–more likely in presence of asymmetrical neurologic signs

Question 29

unless it is ruled out what does a comatose trauma pt have?

Answer 29

intracranial bleed! brain CT or MRI needed, in addition to ABCs

Question 30

mechanism of hyperventilation to ICP

Answer 30

-intracranial blood volume is reduced since hypocarbia causes arterial vasoconstriction

Question 31

mechanism of osmotic diuretics (mannitol) on ICP

Answer 31

-reduced cerebral water volume, by osmotics effects on intact BBB in nml brain tissue

Question 32

iv corticosteroids (dexamethasone) vs edema

Answer 32

-dex can counter edema produced by a cerebral tumor, abscess, or encephalitis (not from ischemic infarction or hemorrhage)

Question 33

define brain death

Answer 33

-irreversible loss of function for both cerebrum and brain stem

Question 34

causes of brain death

Answer 34

• hemorrhage from trauma
• uncontrolled HTN
• ruptured berry aneurysm
• large/multiple ischemic infarctions
• meningoencephalitis
• anoxia f/m cardiac arrest…fragile gross brain

Question 35

where is there evidence of herniation caused by edema

Answer 35

temporal lobes and foramen magnum

Question 36

where is necrosis most severe

Answer 36

cerebral cortex and cerebellar folia

Question 37

red neurons vs Purkinje cells

Answer 37

• ischemic red neurons: found in cerebral cortex and appear eosinophilic and shrunken
• cerebellum Purkinje cells: ischemic or absent

Question 38

What is necessary for brain death declaration

Answer 38

• apparent cause should be known and must be of sufficient severity to account for the irreversible coma
• no neurological improvement despite adequate tc of any reversible causes of coma (such as drug intoxication, circulatory shock, or hypothermia–core temp <32C)

Question 39

what is the generally accepted observation period when the etiology of coma is known and no reversible causes require tx?

Answer 39

SIX HOURS

• 7d-2mo: 48 hr
• 2mo-1yr: 24 hr
• > 1yr: 12-24 hr

Question 40

bedside neurological exam in a brain dead pt

Answer 40

-shouldnt show any hint or suggestion of cerebral function in a comatose pt unresponsive to painful stimuli
=NO: decorticate/decerebrate, sz, swallowing, yawning, vocalization, pupillary rxn to light, light and corneal reflex, dolls eyes, cold caloric, gag reflex
-all CN or BS reflexes must be absent sans spontaneous respirations

Question 41

what specific testing can be used to verify apnea?

Answer 41

1. give ventilated pt 100% oxygen for 10mins to create an oxygen reserve in lungs and test baseline ABG
2. d/c vent while 100% is still supplied though tubing
3. if ensuing hypercarbia induces respiratory movements apnea is RULED OUT
4. If no respiratory movements happen after 10 mins test another ABG
5. apnea is CONFIRMED if no breathing observed despite reaching pCO2 of 60mmHg (or pCO2 20mmHg above baseline)

Question 42

When are confirmatory tests of brain death used?

Answer 42

when bedside examination of CN and BS reflexes are hard to do–severe facial and ocular trauma or edema.
-also should always be done in comatose kids <1yo

Question 43

What are two classical confirmatory tests of brain death

Answer 43

1. a flat line or isoelectric EEG after 30 mins of recording

2. cerebral angiography which showed failure of any intracranial blood flow over a 10 min period d/t a fatal brain edema

Question 44

What is often the currently preferred confirmatory test?

Answer 44

a radioisotope brain scan