GS - Diagnosing death using neurological criteria Flashcards
What is the function of the brainstem ?
When considered at the most basic level the brain-stem provides a structural link between the cerebral hemispheres superiorly and the spinal cord inferiorly
What are the 3 components from superior to inferior that makes up the brainstem ?
Midbrain
Pons
Medulla oblongata
Where does the mid brain pass through and what
are its 2 halves known as sand what runs through these ?
The mid-brain passes through the tentorial notch and consists of two halves known as the cerebral peduncles. Within these structures run three descending tracts
What 3 descending tracts run through the cerebral peduncles ?
- corticospinal tract (umn of spinal nerves supplies motor function limbs & torso)
- corticopontine tract (umn of cranial nerves V, VII & XII)
- corticobulbar tract (umn of cranial nerves supplies motor function to face, head & neck)
Are the 4 swellings of the tectum posterior to the cerebral aqueduct and what reflexes are associated with them?
Two superior colliculi concerned with visual reflexes
Two inferior colliculi concerned with auditory reflexes
What does the reticular formation do?
The reticular formation which plays a key role in consciousness, arousal and the transmission of pain is located in the pons.
What separated the two inferior components of the brainstem and what runs in this furrow?
A transverse furrow separates the two inferior components of the brainstem. Three cranial nerves run in this furrow.
1. VI abducent
2. VII facial
3. VIII vestibulocochlear
Where does the most inferior component of the brainstem join the spinal cord and what does it contain ?
The most inferior component of the brain-stem joins with the spinal cord at the level of the atlas. It contains the centre for cardiorespiratory control.
Where are all of the cranial nerve nuclei located and what are the 2 that don’t follow this rule?
With the exception of the olfactory & optic nerves all cranial nerve nuclei are located in the brain stem
What cranial nerves do the autonomic fibres run along side ?
Autonomic fibres are also located in the brainstem principally running with the following cranial nerves:
III, VII, IX, X
What are the 3 main functions of the brainstem and why is it important ?
The brain stem has a number of key functions which are critical for life:
1. Regulation of arousal and conscious awareness (reticular activating system)
2. Maintenance of spontaneous respiration and cardiovascular control
3. Transmission of motor and sensory impulses to and from central and peripheral nervous
systems
How may the brain be damaged?
The brain is particularly susceptible to severe and permanent damage due to its high metabolic oxygen demand, the effects of swelling with in a fixed rigid bony container (skull) and the inability of neuronal tissue to regenerate.
What is the definition of death and how des this relate to the brainstem ?
One definition of death is the irreversible loss of the capacity for consciousness, combined with irreversible loss of the capacity to breathe.
When the brain-stem has been damaged such that its integrative functions (which include the neural control of cardiac and pulmonary function and consciousness) are irreversibly destroyed, death of the individual has occurred and the heart will inevitably stop beating although the time over which this occurs may vary considerably.
Brain death criteria - allows discontinuation of intensive care treatment in a patient with no chance of recovery and allows the family to understand that the patient has died. Diagnosis of brain-stem death allows consideration of organ donation although the two processes must be kept very clearly separate from each other.
Who must carry out brain-stem death testing or diagnosis of death by neurological criteria ?
Two qualified doctors who have been fully registered with the General Medical Council for at least five years. The doctors must be competent at the procedure and one must be a consultant. Neither doctor should be a member of a transplant team or have any other potential conflict of clinical interest. The testing is carried out by the doctors together and completed successfully on two separate occasions. There is no defined time required to separate the two tests.
What are the criteria for diagnosing death?
The diagnosis of death by neurological criteria is a clinical procedure (i.e. investigations such as blood tests, EEGs, or scanning techniques are not a required element). There are three essential components:
- Fulfilment of essential preconditions: The patient has suffered irreversible brain damage from a known cause and is deeply unconscious, apnoeic and mechanically ventilated. Common causes of brain-stem death include hypoxic brain damage, intracranial haemorrhage, trauma and ischaemic stroke.
- Reversible influences on conscious level must be excluded. These include sedative drugs, hypothermia (temp must be >340C at time of testing) and significant endocrine and metabolic disturbances
- Formal testing for the absence of brain stem activity is carried out once the preconditions are met and reversible influences have been excluded.
Also test for absence of brain stem reflexes (more coming up)
What are the brain-stem reflexes that we check to be absent when assign death ?
Testing for absence of brain-stem reflexes: (6 tests)
Clinical examinations 1-5 test TWO cranial nerves. Identify them.
- The pupils are fixed and do not respond to sharp changes in the intensity of incident light. Cranial nerves: optic & oculomotor
- There is no corneal reflex – care should be taken to avoid damage to the cornea.
Cranial nerves: trigeminal & facial - The oculo-vestibular reflexes are absent.
No eye movements are seen during or following the slow injection of at least 50mls of ice cold water over one minute into each external auditory meatus in turn. Clear access to the tympanic membrane must be established by direct inspection and the head should be at 300 to the horizontal plane, unless this positioning is contraindicated by the presence of an unstable spinal injury.
Cranial nerves: vestibulocochlear & oculomotor - No motor responses within the cranial nerve distribution can be elicited by adequate
stimulation of any somatic area. No motor response can be elicited within the cranial nerve
or somatic distribution in response to supraorbital pressure. Cranial nerves: trigeminal & facial - There is no cough reflex response to bronchial stimulation by a suction catheter placed down the trachea to the carina, or gag response to stimulation of the posterior pharynx with a spatula.
Cranial nerves: glossopharyngeal & vagus - The process for testing the respiratory response to hypercarbia (apnoea test) should be the last brain-stem reflex to be tested and should not be performed if any of the preceding tests confirm the presence of brain-stem reflexes. The patient is disconnected from the ventilator allowing the pCO2 to rise above 6.5 kPa and the pH to fall below 7.4. Oxygenation is maintained by insufflating oxygen down the tracheal tube via a catheter. The patient is observed for respiratory effort for a period of five minutes.
The pupils are fixed and do not respond to sharp changes in the intensity of incident light. What nerves does this test?
optic & oculomotor
There is no corneal reflex – care should be taken to avoid damage to the cornea. What nerves does this test?
trigeminal & facial
The oculo-vestibular reflexes are absent.
No eye movements are seen during or following the slow injection of at least 50mls of ice cold water over one minute into each external auditory meatus in turn. Clear access to the tympanic membrane must be established by direct inspection and the head should be at 300 to the horizontal plane, unless this positioning is contraindicated by the presence of an unstable spinal injury. What nerves does this test?
vestibulocochlear & oculomotor
No motor responses within the cranial nerve distribution can be elicited by adequate
stimulation of any somatic area. No motor response can be elicited within the cranial nerve
or somatic distribution in response to supraorbital pressure. What nerves does this test?
trigeminal & facial
There is no cough reflex response to bronchial stimulation by a suction catheter placed down the trachea to the carina, or gag response to stimulation of the posterior pharynx with a spatula. What nerves does this test?
glossopharyngeal & vagus
