Neurophysiological assessment of coma : AH Neurophysiological assessment of coma Definitions : AH Definitions Consciousness is the state of awareness of self and the environment and coma is its opposite. That is the total absence of awareness of self and the environment even with external stimulation. Between these poles there is : : AH Between these poles there is : Confusion…………bewildered but attentive
delerium…………..irritable,out of contact but alert
obtundation……….reduced alertness, slowed responses
stupor……………..responsive only with vigorous and repeated stimuli Other states of importance : AH Other states of importance Vegetative state……The return of alertness but no evidence of cognitive function
Apallic syndrome…..Essentially the same as vegetative state
Akinetic mutism……Silent alert immobility, minimal motor response to noxious stimulation.
Locked in syndrome..Evidence of cognitive function as distinct from akinetic mutism. The state of consciousness reflects : AH The state of consciousness reflects 1. The level of arousal
Arousal depends on the integrity of brain stem function, in particular the ARAS
2. Cognitive function
Cognitive function predominantly depends on cortical and thalamocortical integrity. Clinical approach to the comatose patient : AH Clinical approach to the comatose patient Pathology must involve either
Diffuse…………………...toxic/metabolic Patients can usually be categorised into these groups : AH Patients can usually be categorised into these groups History
Assessment of arousal
deep tendon reflexes Supratentorial : AH Supratentorial Initiating signs usually of focal cerebral dysfunction
Signs of dysfunction progress rostral to caudal
Motor signs often asymmetrical Slide 9: AH fig18 Slide 10: AH Fig 19 Slide 11: AH Fig 20 Slide 12: AH Fig 21 Slide 13: AH Fig 22 Slide 14: AH Fig 23 Subtentorial : AH Subtentorial History of brain stem dysfunction or sudden onset coma
Oculovestibular features often precede or accompany coma
Cranial nerve palsies present
Bizarre respiratory patterns common and at onset Toxic/Metabolic : AH Toxic/Metabolic Confusion,delirium,stupor,obtundation precede motor signs
Pupillary responses usually preserved
motor signs usually symmetrical
Acid-base imbalance with hypo or hyperventillation Psychogenic unresponsiveness : AH Psychogenic unresponsiveness eyelids actively close
icewater calorics induce nystagmus
EEG normal The role of EEG in diagnosis : AH The role of EEG in diagnosis Differentiates coma from psychogenic unresponsiveness
Identifies non convulsive status epilepticus
Bilateral delta indicates the patient is either deeply asleep or unconscious
A normal EEG rules out metabolic brain disease as a cause of coma.
A “normal” EEG in delerium strongly suggests an alcohol or drug withdrawal state
The degree of slowing usually reflects the severity of the metabolic encephalopathy Slide 19: AH In diffuse metabolic encephalopathy the EEG is usually more sensitive than the clinical assessment with slowing still present when the patient has returned to clinical normality. The role of EEG in prognosis of anoxic cerebral injury. : AH The role of EEG in prognosis of anoxic cerebral injury. Five Grades Grade 1. “Near normal” : AH Grade 1. “Near normal” Excellent prognosis unless “locked in”or alpha pattern coma Grade 2. Theta dominant : AH Grade 2. Theta dominant If reactive the prognosis is very good
If nonreactive survival is usually accompanied by neurological sequelae Grade 3. Delta dominant : AH Grade 3. Delta dominant If reactive the prognosis can be good
If non-reactive the prognosis is grave provided drugs and hypothermia excluded. Grade 4. Burst suppression & continuous bilateral periodic sharp waves : AH Grade 4. Burst suppression & continuous bilateral periodic sharp waves Prognosis grave if drugs and hypothermia excluded
Often associated with clinical myoclonus. Slide 25: AH Slide 26: AH Slide 27: AH Grade 5. Isoelectric : AH Grade 5. Isoelectric Prognosis grave if drugs and hypothermia excluded. Rare Variants : AH Rare Variants Alpha pattern coma : AH Alpha pattern coma Anterior predominance
Unreactive alpha frequency activity.
Rare survivors but only if brain stem reflexes intact. Slide 31: AH Theta pattern coma : AH Theta pattern coma Usually elderly
5 Hz theta with low amplitude burst suppression morphology
Grave prognosis Slide 33: AH Spindle coma : AH Spindle coma Usually head injury, rarely anoxic injury
resembles stage II sleep
prognostically benign. The role of EEG in coma prognosis in anoxic injury : AH The role of EEG in coma prognosis in anoxic injury The difficult group are grade II nonreactives and grade III. These are also the most common groups.
SEPs are useful to further define the prognosis in these groups. The role of EEG in prognosis in severe head injury : AH The role of EEG in prognosis in severe head injury EEG is considerably more limited in prognostication in severe head injury.
Reactivity may be the most useful parameter for classifying outcome into “good” vs “bad”
Good being moderately disabled or better
Bad being worse than moderately disabled. Reactivity can be : AH Reactivity can be Attenuation
Paradoxical (high amplitude slow waves)
90 + % of patients with preserved reactivity of either type have “good”outcomes
90 +% of patients with absent reactivity have bad outcomes.
20 +% have “uncertain” reactivity & 70+ % of these have good outcomes. Slide 38: AH Fig 1 The role of SEPs in anoxic cerebral injury and severe head injury : AH The role of SEPs in anoxic cerebral injury and severe head injury The bilateral absent of the “thalamo-cortical” wave forms (N19, N20, N1)signifies that the patient will not recover to better than PVS………….100% specificity
However sensitivity is low (20-30 %).
Hence the interest in the N70 Slide 40: AH N70 : AH N70 Madl et al
“Of 113 patients with a bilateral N70 peak latency >130 msec or absent all but one had a poor outcome”
Sensitivity of 94% and specificity of 97%
Sherman et al
Using a bilateral N70 peak latency > 176 msec all had a poor outcome
Sensitivity 78% and specificity of 100%