Brain death anatomy and physiology PPT

Brain death is recognized as what 3 points

1. legal definition fo death

2. medical state of complete + irreversible loss of brain fxn

3. prerequisite for organ donation

Debates persist about 3 points:

1. cultural definitions of death

2. standardization of testing

3. ethical challenges w/ life-support tech

Brain death current consensus has 3 points:

1. absent cerebral fxn

2. absent brainstem fxn

3. apnea

cerebral cortex normal fxn

cognition, voluntary movement and sensation! it is the awareness that chooses to move and sensory feedback

brain stem normal fxn

consists of your reticular activating systems (midbrain, pons and medulla) that contains your VRGs and DRGs, firing and terminating breaths as well as a relay system for information. It is possible for information to be in the brain but not move to the stem, classifying as brain dead.

What do each part of the reticular activating systems control and their nerves?

1. midbrain: cranial nerve II functions eye movement + pupillary fxn

2. pons: cranial nerves IV, V, VI, functioning corneal reflex and conjugating eye movement

3. medulla: cranial nerves IX, X, functioning respiration + gag/cough reflex

These receive multiple sensory inputs and mediates wakefulness, often shutting down on long-term brain injuries

five types of brain death:

1. cerebral anoxia

2. cerebral hemorrhage

3. subarachnoid hemorrhage

4. trauma

5. meningitis

cerebral anoxia

#1 cause of death

globally swells the whole brain. increased pressure w/I shell escapes only through a hole (foramen ovale)  @bottom where brain stem is, pushing brain stem down it, causing a hernia.

cerebral hemorrhage

bleeding in brain

blood fills up + same thing occurs w/ anoxia: blood fills up → increased pressure → pushes against FO → hernia. this also causes center line b/w BV to be SHIFTED in the brain.

subarachnoid hemorrhage

bleeding/injured BV under crania

bleeding/injury → disruption of BF → hernia

meningitis

viral or bacterial causing global inflammation

importance of global vs focal issue in brain

if issue is GLOBAL: cannot do anything about it

if issue is focal: can target it

mechanism of cerebral death (arrow diagram)

injury → swelling → increased ICP → decreased IBF

Can ICPs be greater than MAP?

NO! ICP>MAP is incompatible w/ life!

>60 = herniate + die

3 conditions distinct from brain death

1. persistent vegetative state

2. locked-in syndrome

3. static encephalopathy 

persistent vegetative state

common in hospital esp w/ chronic trachs

they have normal sleep-wake cycles but don’t respond to stimuli due to diffuse brain injury w/ preservation of brain stem.

locked-in syndrome

ventral pontine infarct (type of stroke)

complete paralysis but w/ consciousness + eye movement ): . This is typically caused by an incomplete blockage b/w cognitive portion + brain stem.

static encephalopathy

results in a minimally responsive state due to diffuse or multi-focal brain injury but w/ preserved brain stem fxn. This allows variable interaction w/ environmental stimuli. This is in b/w locked in syndrome + vegetative state due to variable interaction.

braind death neurological examination 3 clinical prereqs

1. known irreversible cause (MUST know what is wrong before claiming dead)

2. exclusion of potentially reversible conditions either by:

   1. drugs/poison (can maybe rid system of it)

   2. electrolyte or acid-base imbalance

   3. endocrine disturbances (make you seem dead)

3. WARM temp (>35C, body preserves itself so need to warm up body to determine death)

brain death neurological examination: coma (3 tests)

no response to stimuli. this is tested by either:

1. nail bed pressure (PREFERRED, unlikely to harm)

2. sternal rub

3. supra-orbital ridge pressure (press on eyebrows)

brain death neurological examination: absence of brain stem’s 5 reflexes

1. pupillary reflex

2. eye movements (vestibulo-occular)

3. facial sensation and motor response

4. cough/gag reflex

pupillary reflex

pupils should SHRINK w/ light. if BOTH eyes remain DILATED, this would be lack of reflex

vestibule-ocular reflex 2 tests

1. doll’s eyes (oculo-cephalic)

   1. mechanical/gravitational stimuli! move pt. head for them and their eyes should STAY CENTERED

2. cold calorics

   1. thermal energy stimuli! put 50cc of super cold water in ear and BOTH eyes should move TOWARDS the watered ear. must wait 5 minutes before evaluation.

facial sensation and motor responses (3 responses)

1. corneal reflex

   1. irritates eye + blinks due to touching of cornea or by dropping saline in it)

2. jaw reflex (push against jaw to test brainstem reflex, NOT the same as grimace to pain)

3. grimace to supraorbital or temporo-mandibular pressure (requiring awareness + processing)

apnea testing prerequisites (3)

1. core body temp >35C

2. SBP >90mmHg

3. normal electrolytes + PCO2

apnea testing qualifications/contraindications (6)

1. absent brain motor responses + brainstem reflexes

2. body temp

3. hemodynamically stable w/ or w/o vasopressors 

4. PaO2 >200mmHg on 100% FiO2

5. >7.30pH (cannot use vasopressors w/o this!)

6. absence of cervical spinal cord injury

apnea testing considerations

physician must be present + written order is required. ABG also needs to be drawn before and @end of trial

if apnea test cannot be performed?

If too much PEEP or O2 needs as cannot remove vent for 10minutes:

1. brain flow scan

2. 4 vessel cerebral angiogram

apnea trial steps (6)

1. normalize PaCO2 + pH

2. ABG (Estimate time required to reach appropriate PaCO2)

3. hyperox: 10min 100% FiO2 ON VENT

4. PaCO2 must be ABOVE 60mmHg + INCREASED BY 20pts (45→60? fail, 45→65? pass. 30→50? fail, 30→60, pas). IF this does not happen, must repeat test!

5. disconnect pt from mech vent + place on 100% O2 via blow-by/flow-inflating/anesthesia bag for calculated time

6. observe for spont breathing.

   1. no RR = ABG

   2. RR, hypotension or arrhythmias = returns to vent

Do dead people produce CO2?

NO!!!!

After apnea testing declared pt. dead

heart still beats + continue to perfuse and oxygenate

confounding clinical conditions (6)

1. facial trauma

2. SCI

3. pupillary abnormalities

4. CNS sedatives or NM blockers (need to wait 24h before)

5. hepatic failure (brain dead or drugs?)

6. pulm disease

observations that can be misinterpreted as evidence for brain stem fxn (4)

1. sweating/blushing

2. deep tendon reflexes

3. spontaneous spinal reflexes (triple flexion)

4. babinski sign (toes fan out)

special circumstances

1. children >1yr

   1. same criteria but physician must be qualified for NICU and can mandate a second exam

2. 30d-1yr old

   1. minimum clinical criteria = OCR

   2. repeat exam recommended by another physician/time

   3. extend time interval or perform ancillary test if uncertain/confounders factoring in

   4. specialists certified w/ infants w/ brain injury

ancillary test

alternative test to one that otherwise cannot be conducted. this is used when proximate cause of coma is not known or when confounding clinical conditions limit examination

GOLD STANDARD: global absence of intracerebral BF through cerebral angiography (go in vessel + look under fluoroscopy) or radio-isotope scan (BF = black, no BF = white).

ancillary test types

1. EEG

2. cerebral angiography 

3. technetium-99 isotope brain testing

4. MR angiography

5. transcranial US

6. somatosensory evoked potentials