DEFINITIONS
Consciousness may be defined as awareness of oneself and one's
environment. Consciousness appears to have two components: content and arousal.
The content of consciousness appears to be a cortical function. The arousal of
consciousness, on the other hand, is thought to be predominantly a brain stem
function involving the ascending reticular activating system (ARAS), a diffuse
polysynaptic network surrounding the aqueduct in pons and midbrain. Thus,
impaired consciousness occurs with disorders of the ARAS or of both hemispheres.
Disturbances of the arousal of consciousness lead to stupor or coma.
Coma - Unarousable unresponsiveness.
Stupor - May be defined as unresponsiveness from which a patient may only be
roused by repetitive and vigorous stimulation.
NEUROLOGICAL EXAMINATION
While a general neurological examination may give important clues as to the
cause or severity of the coma (e.g., retinal appearances of severe
hypertension), four sets of observation are directly relevant to examination of
the unconscious patient.
1. Assessment of the depth of the coma itself
This may be judged by reference to the patient's eye opening, verbal and
motor responses. First, the patient's first name should be spoken to see if
he/she may be aroused. If the patient do not arouse to verbal stimuli, painful
stimuli will be required, and probably the least traumatic of these are
supraorbital pressure and nail bed compression.
Eye Opening: In
the unconscious patient, the eyelids are tonically maintained closed, and if the
examiner opens them, slowly close again. Sudden closing or blepharospasm
suggests either psychogenic coma or mild impairment of consciousness.
Verbal Response:
This should be graded as absent, incomprehensible (i.e., no recognizable words),
inappropriate or normal.
Motor Response:
The patient should be observed for any spontaneous motor activity. If there is
no spontaneous, activity, a painful stimulus can be applied (e.g., nail bed
pressure) and the motor response observed. The motor responses may thus be
graded as absent, present and either non-localizing or localizing (i.e.,
actively trying to move away from a painful stimulus), extensor (i.e., extension
at the elbow, often accompanied by pronation or the forearm), or flexor (i.e.,
flexion at the elbow and wrists).
2. Vegetative Function
Centers directly important in the autonomic control of blood pressure, pulse,
respiration, and temperatures are situated in the brain stem. Abnormalities of
these may be of use in localizing and prognostic significance in the unconscious
patient.
Respiration:
Metabolic coma can cause a variety of abnormalities of respiratory pattern such
as the kussmaul breathing of diabetic ketoacidosis and the hyperventilation
associated with salicylate intoxication. Structural lesions in the nervous
system classically cause specific abnormalities at different levels. Bilateral
cortical dysfunction predisposes to Cheyne Stokes respiration. Midbrain damage
leads to "central neurogenic hyperventilation," pontine lesions to irregular or
"ataxic" breathing, and medullary damage leads to hypoventilation or apnea.
Pulse and Blood Pressure: Hypotension may be a
contributing factor to the patient's unconscious state, or may result from
medullary depression as occurs in severe barbiturate intoxication. Hypertension
may reflect the disease process responsible for the coma, or may be a result of
the brain stem dysfunction itself. Cushing showed that raised intracranial
pressure produces a corresponding increase in systolic and diastolic blood
pressure. The accompanying pulse and respiratory rate are usually slow (Cushing's
triad of increased intracranial pressure is hypertension, bradycardia and apnea).
Temperature:
Pyrexia may reflect the disease process responsible for coma such as meningitis
or septicemia, or may, as with blood pressure, reflect abnormality of brain stem
function. Following severe head injury, hyperpyrexia and sweating are common
findings.
3. Brain Stem Reflexes
Deep tendon reflexes in the limbs are spinal reflexes, and though they may
help in lateralization of a lesion, their value in the unconscious patient is
limited. Reflexes dependent on nerve cell nuclei in the brain stem are often
more useful; dysfunction of the ascending reticular activating system is often
accompanied by abnormalities of these reflexes. For practical purposes, brain
stem reflexes can be discussed under three headings: pupillary reactions, eye
movements, and the corneal reflex.
Pupillary Reactions:
Examination should be aimed at determining the size of each pupil and its direct
and consensual reaction to the light. The size and equality of the pupils may
give localizing clues. For example, pinpoint pupils strongly suggest a pontine
lesion, a fixed unilateral dilated pupil is suggestive of an uncal herniation
with compression of the peripheral third nerve, and bilateral dilated fixed
pupils are suggestive of a tectal lesion. The reaction of the pupils to light
may give valuable information about the cause of the coma. Apart from
anticholingeric poisoning and anoxic insults, the pupils remain reactive to
light in nearly all types of metabolic coma, even in the abeyance of other
neurological responses.
Eye Movements:
Spontaneous eye movements may occur in light coma; these are slow, usually
horizontal excursions termed roving eye movements. Sustained lateral conjugate
deviation of the eyes suggests disease of the ipsilateral cerebral hemisphere or
contralateral pons. Downward deviation of the eyes with convergence is seen with
thalamic lesions. Ocular bobbing (rapid downward movements, slow return to
primary position) classically occurs with pontine lesions. After spontaneous eye
movements are noted, reflex movements should be invoked by two mechanism. The
first of these is the so-called "doll's head maneuver" (a.k.a oculocephalic
reflex), which consists of rotating the head from side-to-side. In light coma,
the eyes make full horizontal conjugate excursions opposite to the rotational
maneuver (e.g., turning the head to the right causing conjugate deviation to the
left, and visa versa). As the level of consciousness deteriorates, movements
become less and eventually the eyes become less and eventually the eyes become
fixed at a mid-position. The second method of invoking eye movements is by
irrigating the external auditory meatus with ice-cold water (oculovestibular
reflex). The tympanic membrane should first be checked to see that is it intact,
and then initially 10 ml of iced water should be introduced slowly. In coma, the
"normal" reaction is conjugate deviated toward the irrigated ear. If the
impairment of consciousness is very mild or in psychogenic unresponsiveness,
nystagmus may be present with the rapid phase away from the side of caloric
stimulation. In very deep metabolic coma, or in structural disease of the
brainstem, the response may be absent.
The Corneal Reflex:
Look for Bell's phenomenon - upward deviation of the globes which implies intact
connections from cranial nerve V to cranial nerve III and lid closure -which
implies intact connections from cranial nerve V to cranial nerve VII. Look for
asymmetries in the reflex.
4. Abnormal Motor Activity
Included here are epileptic seizures, tremor, and asterixis (flap). Epilepsy,
whether focal or generalized, is a relatively common finding in coma from a
variety of causes; widespread myoclonic jerking is more commonly seen in coma
due to anoxia; asterixis is most common in metabolic coma, particularly hepatic
failure, uremia, and cardiac failure.
An important point to remember in examining the unconscious patient is that
having documented all the above findings the patient's prognosis can only be
judged according to the progress the patient makes. It is therefore essential to
carry out serial examinations, in the acute phase, at intervals of a few hours,
recording the finding. In this way, the patient's progress will be determined. |
