Mod 8 Brain Death Flashcards
What are common causes of Brain death?(4)
- Massive head trauma
- Intracranial hemorrhage
- Course of a head injury (Variable and ranges in severity).
- Events that cause rapid and marked brain edema increases brain volume (coning)
What are 2 events that cause rapid and marked brain edema that increases brain volume?
- Herination and infarction of the brain stem as it is forcibily displaced from its original location aka coning
- Loss of cerebral perfusion pressure as intercranial pressure exceeds mean arterial blood pressure
What is refractory hypoxemia?
Pts blood oxygen levels (arterial oxygenation) remain dangerously low despite intensive medical interventions.
What function does the Cerebral Cortex have?
- Higher brain function (decision making and speech)
- Cognitive function (memory)
- Motor function
What function does the Mid brain have?
- Sits underneath the cortex
- Limbic system (Fight or flight and rest and digest)
- Emotional center of the brain (fear, anger, bonding)
What function does the brain stem have?
- Controls reflexes
- Breathing, sympathetic/parasympathetic function
- Functions you don’t need to “think” about
What are 3 definitions of death? (3)
- Traditional heart lung failure
- Whole brain death
- Higher brain death
What is Heart Lung Failure?
No heart & no breathing = dead
- Can be hastened by pharmalogical factors (i.e inotropes) or mechanical ventilation
What is Higher Brain Death?
- What kind of support is needed?
Irreversible loss of consciousness
- Injury to Cortex and Midbrain
- No clinical test currently to define higher brain death
- Varying levels of support, but Pts w/higher brain death typically require tracheostomy
What is Whole Brain Death?
The irreversible loss of all functions of the brain, including the brainstem.
- Coning
- Artificial support is the only thing sustaining life
- No purposeful movement (some spinal reflexes)
- Apneic
- May or may not be able to sustain heart beat independently
What is Coning?
Pressure on brainstem due to tonsillar herniation.
- Apparnetly it literally cones outward through the space , hence cone.
What factors should be evaluated after making changes on a Pt w/severe brain injury? (5)
- Sedation/Paralytics (consider renal/liver failure) -> do we want to save for organ transplant?
- Pupillary response
- Response to painful stimuli
- Breathing above set ventilator RR
- Gag/Cough reflex
What are clinical diagnostics for declaring brain death? (3)
- Deep, unresponsive coma
- Absent brain stem reflexes
- Apnea test w/absence of respirations
What Ancillary tests help confirm brain death? (4)
- CT angiography
- EEG
- Radionuclide V/Q Scan
- MRI
What factors and reversible etiology mimic brain death and when absent be used to confirm brain death? (4)
- Sedation/Neuromuscular block
- Hypothermia
- Major metabolic disturbances
- Shock
What brain stem reflexes can you test to determine brain death?
- Pupillary signs
- Ocular movements (Oculocephalic reflex, Vestibulo-ocular reflex)
- Facial sensory and motor responses
- Pharyngeal and Tracheal Reflexes
What pupillary response should you expect with brain death?
Pupillary light reflex must be absent in brain death.
What would Pupillary sign should you expect from a CN III and CN II lesion?
How do you test the Oculocephalic Reflex?
- What is normal?
Reflex elicited by rapidly and vigorously turning the head to 90 degrees on both sides gently
- The normal response is deviation of the eyes to the opposite side of the head turning
- Known as the Doll’s Eyes Reflex
What is the general term for the Dolls Eye Reflex?
Oculocephalic Reflex
What is a absent Oculocephalic reflex indicative of?
- How does a absent reflex reflect?
Absence of reflex infers brain death.
- Absence presents as no eye movement in response to head movements. Normal response it to shift eyes in the opposite direction.
What does the Caloric test evaluate?
The Oculovestibular reflex.
What is the procedure of the Caloric test?
- Normal response/result?
The Oculovestibular reflex is elicited by elevating the head 30 degrees and irrigating both tympanic membranes (ears) w/at least 20 mls of iced saline or water.
- A normal response for the caloric test would be for the eyes to turn towards the irrigated ears
What is a absent Oculovestibular reflex indicative of?
- How does a absent reflex reflect?
Absent Oculovestibular reflex is indicates brain death.
- Absence will have no deviation of the eyes in response to ear irrigation (during the caloric test).
How long should the Oculovestibular Reflex be observed?
Up to 1 minute after each ear irrigation, with a 5 minute wait between testing of each ear.
Left off @ slide 18
Which facial sensory and motor responses would be tested for brain death?
The absence of the Corneal reflexes and Jaw reflexes would indicate brain death
How is the Corneal Reflex tested?
Using a cotton tipped swab to stimulate the cornea.
- Also referred as “blink reflex”
- Insert image from slide 18
How are Jaw Reflexes tested?
Using a reflex hammer to lightly tap the face below midline of bottom lip, just above chin.
- Masseter muscle contraction is a normal response.
What pain responses could you elicit to evaluate facial sensory and motor repsonses? (2)
- Deep pressure to the traps or temporomandibular joint
- Suprorbital ridge and nail bed stimulation ineffective
What do you evaluate for the Pharyngeal and Tracheal Reflexes?
- Absence?
Gag Reflex and Cough Reflex.
- Could indicate brain death or neurological impairment/damage (nerve bundles originate in the neck C9 and C10)
How can you stimulate the cough reflex?
ETT suctioning
How can you stimulate the Gag Reflex?
Posterior manipulation of ETT, yankeur, or tongue depressor
What is a essential component in clinical neurological determination of death (NDD)
- Why is essential?
Apnea Tests (performed by RTs)
- It is essential bc loss of brain stem function results in loss of centrally controlled breathing.
- Last step of evaluation for brain death
What is Apnea Testing?
Pausing in mech ventilation to allow PaCO2 levels to rise for maximal stimulation of brain stem respiratory centres.
- CO2 is a potent stimulus to breath, absence confirms lack of drive.
- Used to confirm brain death
What role does CO2 have in Apnea testing?
- Why do we evaluate CO2?
Respiratory neurons are controlled by central chemoreceptors that sense changes in PCO2 and pH of the cerebrospinal fluid. In turn they accurately reflect changes in plasma PCO2
What factors should be adjusted or taken into account before initiating a Apnea test?
- Correct hypothermia; core should be >=34c
- Correct confounding factors which interfere w/spontaneous respiratory effort (i.e sedatives, toxins, neuromuscular blockers)
- Pre/hyperoxygenate for 5 mins @1.0
- Never do apnea test on hyperthermic Pts
Should you preoxgenate before proceeding with a Apnea Test?
Yes.
- Preoxygenate/hyperoxygenate for about 5 minutes @ 1.0
Why would you want to correct hyperthermia (permissive or otherwise) before starting a Apnea Test?
The risk of reperfusion injury.
- Permissive hyperthermia raises temperature to increase immune response and tissue repair.
- can lead to increased production of reactive oxygen species (ROS) and a more pronounced inflammatory response, potentially contributing to tissue damage rather than preventing it.
What events can occur if Reperfusion injury occurs?
- Snowball affect?
If circulation is restored to ischemic tissue, it can lead to cerebral edema (calcium, glutamate and other things would increase here)
How would you prevent Reperfusion Injury when beginning Apnea Testing?
Permissive Hypothermia
- Reduces metabolic demand (and flow)
- Prevents coning (events that lead to brain death)
What secondary assessment tool can be used for Apnea Tests?
EtCO2. Absence of reading would confirm brain death because they would not be making any respiratory efforts
How is a Apnea test conducted
- Ensure Stable EtCO2 (and PaCO2)
- Pt. removed from ventilator (oxygenated via bagging unit or suction catheter advanced down ETT)
- Apnea is confirmed (positive test)
What does a positive apnea test mean?
- That the patient is not breathing
- The brainstem is not functional anymore
How is Apnea confirmed in Apnea testing?
- What values do we assess based on vitals?
- PaCO2 > 60 mmHg and >= 20mmHg CO2 change from baseline
- pH =< 7.28
- No respiratory effort noted
Why do we observe CO2 changes form a Pts baseline?
They may be CO2 retainers so their normals may be higher.
When would a Apnea Test be discontinued?
- Spontaneous respiratory effort observed
- BP drop that is not controllable via vasopressor use (MABP < 60 mmHg and systolic < 90 mmHg)
- SpO2 < 90 OR PaO2 < 60 mmHg
