9.1 · General effects: Manifestations of deteriorating brain function

Consciousness

State of awareness of self and the environment, and being able to orient to new stimuli

Two components of consciousness

Arousal (wakefulness) and content/cognition

Reticular activating system (RAS)

Diffuse network involving the brainstem and thalamus that, with a functioning cerebral cortex, maintains arousal

What loss of arousal indicates

Direct injury to the RAS, or injury to both cerebral hemispheres at the same time

Why a stroke usually does not cause loss of arousal

Damage is to only one hemisphere and the RAS is intact

Selective attention

Ability to select specific information to be processed

Memory (component of awareness)

Ability to store and retrieve information

Executive attention

Ability to maintain sustained attention, remember instructions, and possess self-control

Level of consciousness (LOC)

Combined measure of both arousal and cognition

Coma

Completely not arousable

Stupor

Arousable only to pain

Obtundation

Lowered level of arousal; sleepy

Delirium

Restlessness, hallucinations, delusions

Confusion

Disorientation, fuzzy thinking, poor response to current stimuli

Glasgow Coma Scale

Scores eye opening, verbal response, and motor response; total score indicates level of consciousness

GCS score of 15

Normal

GCS score of 13-14

Mild head injury

GCS score of 8-12

Moderate head injury

GCS score below 8

Severe head injury

GCS score of 3

Lowest possible score; no response, brain death

Brain death

No recovery possible and the brain cannot maintain internal homeostasis

Clinical criteria for brain death

Well established underlying pathology, deep unresponsive coma with absent motor reflexes, absent brainstem reflexes, requires mechanical ventilation (apnea test), and no other causes such as drugs or shock

Cerebral death

Irreversible coma; brainstem may still maintain homeostasis but the person can never respond meaningfully to the environment

Persistent vegetative state

Complete unawareness of self or environment; sleep-wake cycles present and brainstem reflexes intact, but bowel and bladder incontinence; very slim chance of recovery

Minimally conscious state

May follow simple commands, manipulate objects, gesture, and occasionally have intelligible speech; may follow a persistent vegetative state

Locked-in syndrome

Complete paralysis of voluntary muscles except eye movement; fully conscious with intact cognition but cannot communicate by speech or body movement

Cheyne-Stokes breathing

Alternating periods of apnea and tachypnea from higher brain injury, due to response to blood carbon dioxide levels

Neurogenic hyperventilation

More than 40 breaths per minute when inspiratory and expiratory centers are continuously stimulated; lesion between midbrain and brainstem

Pupillary changes in brain injury

Response to light can be fixed, dilated, pinpoint, or unequal; helps determine location and extent of brain damage

Pupils in severe hypoxia

Dilated and fixed

"Blown" pupil

One non-responsive pupil from damage or pressure on the oculomotor nerve (cranial nerve III)

Oculocephalic reflex (doll's eye response)

Eyes move opposite from head movement; indicates intact brainstem function

Abnormal oculocephalic reflex

Eyes follow head movement or move independently; assessable only in comatose patients

Decorticate posture

Upper extremities flexed at the elbows and held close to the body, lower extremities internally rotated and extended; severe cerebral hemisphere damage

Decerebrate posture

Increased tone in extensor and trunk muscles, clenched jaw, extended neck, all four limbs rigidly extended; brainstem and midbrain lesions

Why posturing matters

Shows the degree of brain damage as it extends from cerebral hemispheres to deeper structures, the midbrain and brainstem