Disorders of consciousness

Question 1

What is the anatomy of the ascending reticular activating system

Answer 1

The ARAS is located in the midbrain and the pons and projects to the thalamus and the cortex. The intralaminar nuclei of the thalamus maintains arousal. The system contains cholinergic neurons in the tegmentum that project the thalamus and monoaminergic neurons that project from the brainstem to the thalamus, basal forebrain and cortex.

Question 2

What is the physiology of consciousness

Answer 2

Stimulation of the posterior hypothalamus and thalamus causes arousal while lesions in the cuneus and precuneus association cortex are involved in the minimally conscious state. Anterior cingulate lesions result in abulia.

Question 3

What are the three conditions for LOC

Answer 3

The three conditions for LOC are brainstem (removes ARAS), thalamic and bilateral hemispheres (leaves ARAS but cannot project to anything).

Question 4

Define coma

Answer 4

Coma is an unarousable, unresponsive state lasting more than 6 hours. The patient cannot be wakened or respond to any stimuli. They will lack a normal sleep/wake cycle and display no voluntary actions.

Question 5

Define vegetative state

Answer 5

VS is diagnosed after continuing for 4 weeks. It is termed permanent if it lasts > 1 year following TBI or > 6 months following other mechanisms. The patient may demonstrate sleep-wake cycles, have their eyes open and show reflex actions. However, they do not show any real awareness of themselves or their environment and no higher cortical functions.

Question 6

Define minimally conscious state

Answer 6

MCS is severely altered consciousness. There may be minimal evidence of awareness and inconsistent but reproducible responses to surroundings. They may be able to follow simple commands and answer yes/no, as well as being able to react in response to emotional stimuli. They will often show an eye movement pursuit. This is diagnosed after continuing for 4 weeks and is permanent if it lasts > 5 years in most cases and > 3-4 years in diffuse axonal injury.

Question 7

What are the pre-conditions for diagnosing VS or MCS

Answer 7

The cause of the condition must be established as far as possible. The cause must not be reversible. Careful assessment of the patient must be performed by a trained assessor under appropriate conditions using valid tests.

Question 8

What are some common causes of PDOC

Answer 8

Some common causes of permanent disorders of consciousness include: trauma (direct impact or acceleration injury), vascular damage (ICH, SAH, CVA), hypoxia or hypo-perfusion (cardiac arrest/shock), infection/inflammation (encephalitis, vasculitis), toxic/metabolic (drug/alcohol poisoning, severe hypoglycaemia).

Question 9

What are some chronic states of altered consciousness

Answer 9

Chronic states of altered consciousness include: During the final stages of lewy body dementia, hypersomnia (Kleine-Levin syndrome), Akinetic mutism (catatonia), Apallic syndrome (wipe out neocortex).

Question 10

What can mimic disorders of consciousness

Answer 10

Locked-in syndrome can mimic PDOC because the patient may be conscious but they do not show any voluntary movement. This is caused by a higher brainstem pathology. The patient will have retention of blinking and vertical eye movements. The cause of LIS is often central pontine myelinosis from rapid overcorrection of hyponatraemia.

Question 11

How do you do a general assessment of PDOC

Answer 11

You would assess the patient as follows: collateral history, observations, general exam, GCS, meningism, trauma, fundoscopy/pupils, tone, reflexes, brainstem signs

Question 12

What are the brainstem signs in PDOC

Answer 12

Breathing rhythm changes, gaze orientation dysfunction, eye movement disorders, oculocephalic reflex would be absent.

Question 13

What investigations would you do for a patient with PDOC

Answer 13

You would investigate: lab tests for acidosis, check abnormal sodium, calcium, CO2 or glucose, drug screen, blood cultures and imaging (EEG and CSF).

Question 14

What is the immediate management for a patient with PDOC

Answer 14

Oxygenation, ABC, correct BP/temp, give glucose, correct sodium/calcium and eliminate toxins, given naloxone if overdosed on opioids, give flumenazil if overdoses on benzos, correct ICP, check for infection, consider neurosugery.

Question 15

What is long-term management for a patient with PDOC

Answer 15

Tracheostomy, PEG, bladder bowel infection and DVT prevention, wean from ventilator, avoid MRSA and vancomycin resistance, prevent contractors, protect skin, avoid neurostimulation including drugs

Question 16

What predicts poor prognosis in PDOC

Answer 16

Myoclonic status, absent corneal reflex at 3 days, absent motor reflex at 3 days, absent sensory evoked potential, increased serum neuron specific enolase (neurological outcome)

Question 17

How is brainstem death diagnosed

Answer 17

The cause must be identified and not be reversible, The core body temp must be more than 36.5 so that they are not under hyperthermia, systolic blood pressure must be more than 100mmHg, all brainstem reflexes must be absent and absent respiratory efforts in the presence of hypercarbia.