Coma

Question 1

what are the 4 types of brain lesions that cause coma?

Answer 1

recall the reticular activating system involves the pons, midbrain, thalamus/hypothalamus, and cerebral cortex… therefore, it makes sense that coma can result from a lesion in any one of the following:

1. dorsolateral upper-mid pons
2. paramedian upper midbrain
3. diencephalon (thalamus/hypothalamus)
4. diffuse hemispheric damage

Question 2

injury to the ventral or dorsal pons can cause coma?

Answer 2

reticular activating system runs through DORSAL pons, so a DORSOLATERAL upper-mid pontine lesion can cause coma

Question 3

how will a comatose patient respond to the cold water test?

Answer 3

ice water in ear inhibits vestibular nuclei, so contralateral side becomes hyperactive, pushing gaze TOWARDS the inactive ear

in a normal patient, the frontal eye fields will cause a saccade back towards middle, but in a comatose patient, this will not occur - this indicates injury to the pons

(which, as you recall of course, is part of the reticular activating system, injury to which causes coma!)

Question 4

what are the descriptive levels of consciousness? (5)

Answer 4

1. alert: awake, oriented, following commands
2. drowsy: lethargic but arousable to voice/ light touch
3. obtunded: lethargic, but arousable to vigorous mechanical stimulation
4. stuporous: localizing to deep pain
5. comatose: withdrawal reflexes, abnormal posturing, none or non-localizing responses

Question 5

why do patients with central herniation present with Cheyne Stokes breathing?

Answer 5

[central herniation = diencephalon herniates downward into midbrain]

damage to hypothalamus causes dysfunction of the chemoreceptors that sense CO2 levels

this causes brain to rely on slower chemoreceptors in the wall of the 4th ventricle

so patients will hold their breath until the CO2 gets high enough to trigger these receptors, then hold their breath again when the CO2 levels drop under the threshold —> Cheyne Stokes breathing

Question 6

Cheyne Stokes breathing is characteristic of which type of brain herniation?

Answer 6

central herniation = diencephalon herniates downward into midbrain

damage to hypothalamus causes dysfunction of the chemoreceptors that sense CO2 levels

this causes brain to rely on slower chemoreceptors in the wall of the 4th ventricle

so patients will hold their breath until the CO2 gets high enough to trigger these receptors, then hold their breath again when the CO2 levels drop under the threshold —> Cheyne Stokes breathing

Question 7

earliest sign of uncal herniation

Answer 7

dilation of ipsilateral pupil

[recall uncal herniation is asymmetric - downward herniation of cerebellar uncal]

Question 8

describe the scoring of the Glasgow Coma Scale

Answer 8

Eye:
4+ = spontaneously open
3+ = open to verbal command
2+ = open to pain
1+ = no eye opening

Verbal:
5+ = oriented
4+ = confused
3+ = inappropriate words
2+ = incomprehensible
1+ = no verbal response

Motor:
6+ = obeys commands
5+ = localizes pain
4+ = withdrawal from pain
3+ = flexion to pain
2+ = extension to pain
1+ = no motor response

Question 9

what is the Four Score (developed by Mayo Clinic)?

Answer 9

alternative coma scale to Glasgow, consists of 4 components:
1. eye response
2. motor response
3. brainstem reflexes
4. respiration

Question 10

what are the necessary criteria of declaring brain death? (4)

Answer 10

1. establish irreversible cause of coma
2. exclude confounding factors (CNS depressant drugs, neuromuscular blockade, hypothermia, hypotension, etc)
3. unfavorable neurological examination - lack of CN reflexes, absent or reflexive motor responses to noxious stimuli, NO spontaneous breathing
4. apnea testing - establish no spontaneous respiratory drive off the ventilator (disconnect 8-10 mins)

Question 11

what are the 2 goals of ancillary testing for brain death? (when criteria is met but there is still uncertainty)

Answer 11

1. absent cerebral blood flow - transcranial doppler, cerebral angiogram, nuclear SPECT
2. absent electrical activity - EEG, evoke potentials