Altered States of Consciousness

After completing this article, readers should be able to: During the course of normal interaction with one another, we observe each other’s mannerisms, responses, movements, and communications. In a sense, a person’s behavior is determined by how he or she acts or reacts to internal and external stimuli. What is considered normal behavior is often age-specific and person-specific. For example, the response of a teenager to the early morning “buzz” of an alarm clock is usually a purposeful attempt to shut the alarm off; an infant may cry as a response to the same stimulus. Similarly, children who have certain chronic illnesses, such as static encephalopathy, may have blunted responses as a baseline behavior. Although major changes in behavior are readily apparent to any clinician, subtle changes often are appreciated best by parents and caretakers.Essential to the evaluation of abnormalities in a child’s behavior is an understanding of levels of consciousness. Various terms that define specific conditions or alterations of normal levels of consciousness often are used interchangeably and incorrectly by clinicians and parents alike. Consciousness is a state of awareness of both one’s self and the environment. A child who has a normal level of consciousness can be awakened and is aware of what is happening to and around him- or herself. Alteration of the level of consciousness usually begins with reduced awareness of one’s self, followed by reduced awareness of the environment, and finally by an inability to be aroused. The opposite of consciousness is coma, a state in which a person is unresponsive to all stimuli, including pain.Although consciousness and coma represent the extremes of mental status, there are many abnormal states of consciousness along that spectrum that may, at times, blend imperceptibly into one another. Appropriate use of terminology begins with a proper understanding of the definition of such states of consciousness. Confusion occurs when there is a loss of clear thinking, usually manifested by impairment of cognitive abilities and decision-making. Disorientation often accompanies confusion. In general, disorientation to time occurs first, followed by disorientation to place, and then by deficiency in short-term memory. Loss of recognition of one’s self is a later finding. In delirium, there is a succession of confused and unconnected ideas. Delirious children often have extreme mental and motor excitement, so they become disoriented, fearful, irritable, offensive, or agitated. Lethargy is a state resembling profound slumber, in which the child’s movement or speech is limited. A lethargic child can be aroused with moderate external stimulation but immediately relapses into a state of limited responsiveness. Stupor is a condition of deep sleep or unresponsiveness from which the child can be aroused only with repeated vigorous stimuli. Finally, in coma, the child is unresponsive even to painful stimuli. A persistent vegetative state and coma often are confusing. In both the vegetative state and coma, there is no evidence of self-awareness (no response to communication or purposeful movements) or communication (either verbal or by gestures). However, in the vegetative state, the child’s eyes may open spontaneously, giving the appearance of a state of arousal (albeit poorly sustained and sluggish) as opposed to that of coma, in which the eyes are always closed.An altered level of consciousness in children has many causes, with a fundamental differentiation being between structural and nonstructural (referred to as “medical” in this article) conditions. The mnemonic AEIOU TIPS (tips on vowels) is helpful in listing the major categories of illness or injury to be considered (Table 1). Although these disorders can occur at any age, certain conditions are more prevalent at specific ages. Nontraumatic coma has a bimodal distribution, being most common in infants and toddlers and having another smaller peak in adolescence. Infection either of the brain (encephalitis), meninges (meningitis), or both is the most common cause of altered level of consciousness, accounting for more than one third of nontraumatic cases. (Wong, 2001) Congenital malformations, especially those of the central nervous system (CNS), typically present in the first few postnatal months, but complications from surgical correction of such problems (eg, ventriculoperitoneal shunt obstruction) may occur at any age.Diabetic ketoacidosis, the most common metabolic disorder presenting with alteration of consciousness, can occur at any age but is more common in adolescence. Inborn errors of metabolism, including those that present with electrolyte and glucose abnormalities, typically present in infancy. Prolonged seizures, anticonvulsive therapy, and the postictal state also can alter the level of consciousness.In childhood and adolescence, toxic exposure or ingestion is most common. A toddler has the ability to explore the environment but does not yet have the cognitive ability to know that ingesting pills may be harmful. Many medications (especially those targeted for use in pediatrics) are brightly colored and taste like candy, creating an inviting stimulus for accidental ingestion. Commonly ingested agents that cause an altered level of consciousness are listed in Table 2. Ingestion by adolescents usually is intentional and typically involves over-the-counter medication (eg, acetaminophen, ibuprofen) or psychotropic drugs such as antidepressants.Although the overall incidence of traumatic and nontraumatic coma is similar, the rate of traumatic injury tends to increase throughout childhood. Trauma, especially head trauma, can cause intracerebral, epidural, or subdural bleeding, leading to cerebral dysfunction either by primary neuronal damage or the effects of cerebral herniation or brainstem compression. Intentional trauma (child abuse) always should be considered in any infant presenting with an altered level of consciousness.The clinician can determine the child’s state of awareness by the child’s behavior. The content of a child’s behavior can be inferred by his or her actions and appearance. Normal behavior requires appropriate cognition and affect, enabling children to perceive the relationship between themselves and their environment. This component of behavior is controlled by the cerebral hemispheres.In a typical day, the body goes through a normal cycling of alertness. From a state of wakefulness, it is normal to become drowsy and, eventually, to fall asleep. At some point during sleep (or even during drowsiness), external stimuli are processed through sensory inputs to increase awareness and cause one to be more awake. This cycling of behavior is modulated predominately by the ascending reticular activating system (ARAS), a core brainstem structure that often is considered the “sleep center.” Thus, normal behavior can be thought of as a combination of appropriate “content” and arousal.A useful method of approaching altered level of consciousness is the bulb-switch analogy. Consider the content of behavior (controlled by the cerebral hemispheres) to be a light bulb and the arousal component (controlled by the ARAS) to be a light switch. For the bulb to be lit (at a normal level of consciousness), the bulb has to be functional and the switch on. There are three possibilities if the bulb is not lit (altered level of consciousness): a defect in the bulb itself (diffuse dysfunction of the cerebral hemispheres), a defect in the switch (a localized abnormality of the ARAS), or defects in both the bulb and the switch (global CNS dysfunction). This model also helps differentiate the etiology of the alteration in consciousness. The ARAS is located in the vicinity of several brainstem reflexes, including those for pupillary light reflexes (cranial nerves II and III) and those for reflex eye movements (cranial nerves III, VI, VIII, and the medial longitudinal fasciculus). Thus, preservation of these reflexes suggests that the ARAS is functional. Under this condition, the altered level of consciousness likely is due to a dysfunctional bulb (involvement of both cerebral hemispheres). On the other hand, impingement on the area of the ARAS causes loss of the brainstem reflexes and an altered level of consciousness, even though the cerebral hemispheres are functioning normally. Diffuse cerebral dysfunction usually has a medical basis, such as toxic, metabolic, or infectious causes; compression of the ARAS usually is the result of structural causes (Table 3). About 90% of cases of nontraumatic coma in children are due to medical causes. (Wong 2001)It is important to note, however, that although focal neurologic signs suggest a structural lesion and lack of focality suggests a medical cause, there are many exceptions. For example, structural disorders that may present without focality include acute hydrocephalus, bilateral subdural hematomas, and acute bilateral cerebrovascular disease. Medical encephalopathies that often present with apparent focal neurologic signs include hypoglycemia, hyperglycemia, hypercalcemia, hepatic encephalopathy, uremia, and the postictal state that includes Todd paralysis.The differentiation of structural and medical causes of altered level of consciousness is assessed best by imaging modalities such as computed tomography (CT) scan or magnetic resonance imaging (MRI), which are readily available in most acute-care settings. Although imaging can pinpoint specific structural defects, the presence of cerebral swelling, and focal neurologic abnormalities, it also is important to have a clear understanding of the underlying pathophysiology that accompanies both structural and medical causes of altered level of consciousness. Three major responses (ie, pupillary reflexes, extraocular movements, and motor response to pain) are helpful in evaluating both the level and progression of a child’s state of consciousness. The pupillary reflex is a balance between parasympathetic (pupillary constrictors) and sympathetic (pupillary dilators) innervation. Because the pathways that control this reflex lie adjacent to the brainstem area that controls consciousness, lesions that impinge or affect the brainstem alter pupillary size or the ability of the pupil to react to light. For example, a midbrain lesion interrupts the parasympathetic and sympathetic fibers equally, resulting in pupils that are in midposition and fixed; a pontine lesion primarily interrupts the descending sympathetic fibers, causing pinpoint pupils. Expanding lesions in the temporal area of the brain may cause uncal herniation and compress cranial nerve III, leading to a unilateral dilated and fixed pupil on the side of the lesion.On the other hand, the pupillary reflex is relatively resistant to metabolic insult; although the pupils may be small, they maintain the ability to react to light. Therefore, a child who has unequal, sluggishly reactive, or unreactive pupils should be presumed to have brainstem dysfunction in the area of the ARAS and likely a structural cause for the abnormal level of consciousness, as opposed to a medical cause, which would spare the pupillary reflex. For that reason, the presence or absence of the pupillary reflex is one of the most important findings for differentiating structural and medical causes of altered consciousness.Dysfunction of certain extraocular movements also may accompany structural causes of altered consciousness. In particular, the oculocephalic reflexes are helpful in assessing low brainstem function. For example, when the head is turned to one side in a child who has a functioning brainstem, the eyes move in conjugate fashion, regardless of the level of consciousness. Stimuli from the cervical muscles in the neck, the semicircular canals in the ear, and the cerebellum synapse with the vestibular nucleus in the brainstem. The impulse, then, is transmitted caudally through the medial longitudinal fasciculus (MLF) to the ipsilateral abducens nucleus (cranial nerve VI) that contracts the lateral rectus muscle and abducts the ipsilateral eye. The impulse also continues caudally but crosses the brainstem to synapse with the contralateral oculomotor nucleus (cranial nerve III), which contracts the medial rectus muscle and adducts the contralateral eye. Thus, the eyes move in conjugate fashion (one eye adducts and the other abducts). If there is a brainstem lesion at the level of the MLF, the eyes move dysconjugately when the head is turned. If there is a low brainstem lesion, the eyes do not move at all relative to the head; in this “doll eyes” phenomenon, the eyes appear as if they were painted on the head.Finally, motor response to a painful stimulus can help localize the level of brainstem dysfunction. Lesions at or above the diencephalic level are associated with decorticate posturing, so the legs stiffen and the arms are rigidly flexed at the elbow and wrist. As the lesion moves rostrally to the level of the midbrain or upper pons, the arms and legs extend and pronate in response to pain, in what is called decerbrate posturing. If the lesion extends to the medulla, the child’s muscles are flaccid, and there is no response to painful stimuli.The history and physical examination should focus on identifying both the cause and progression of the altered level of consciousness. Information about the onset of the neurologic symptoms is particularly important. Time of day, location, and duration of initial symptoms may offer clues to the underlying cause. Clearly, a history of trauma directs the differential diagnosis toward traumatic causes. However, especially in the young child, a history of minor trauma may be overlooked. Early morning headaches, dizziness, and somnolence often are seen with increased intracranial pressure. Proximity to a poorly ventilated combustible gas source (home heating system, car exhaust) can cause carbon monoxide poisoning. Dizziness and lethargy following a party or school event should raise suspicion for a toxic ingestion. An abrupt change in the child’s mental status often results from an acute event such as a CNS hemorrhage or obstructive hydrocephalus.A gradual onset of symptoms over hours or days suggests a metabolic, infectious, or toxic cause. Continued clinical deterioration may signal increasing intracranial pressure, systemic infection, or progressive metabolic derangement (acidosis, electrolyte abnormality). A past history of medical conditions associated with altered level of consciousness may be seen in diabetes mellitus, hypoglycemia, hypertension, or uremia.Evidence of drug or alcohol use or availability of prescription or nonprescription drugs should be ascertained. In both intentional and accidental ingestions, there may be no specific history of ingestion. Therefore, the clinician must determine the availability and type of medication in the home. Because ingestions are a common cause of altered mental status in children, a list of important historical questions is shown in Table 4.Key findings on the physical examination can help differentiate structural from medical causes of altered consciousness. Accurate assessment of the child’s vital signs is of paramount importance. If the child is febrile, an infectious cause is likely, although some toxic ingestions (eg, anticholingerics) also can cause fever. The respiratory rate and pattern may be helpful in localizing the level of a brainstem lesion. Because the respiratory center is located in the pons and medulla, compression on this area of the brainstem changes the pattern of respiration. If there is primary cerebral dysfunction, there may be posthyperventilation apnea. As the level of the brain dysfunction progresses from caudal to rostral through the brainstem, the respiratory pattern progresses from Cheyne-Stokes respiration (crescendo-decrescendo pattern followed by intervals of apnea) to central neurogenic hyperventilation (sustained, rapid, deep respiration). In low brainstem lesions, respiratory effort is gasping, irregular, or sporadic.The pulse or blood pressure often is abnormal in cases of impending cerebral herniation. The cranial vault can accommodate a modest increase in intracranial contents caused by brain swelling, cerebral mass, or hemorrhage. 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After initial assessment and on the specific diagnosis and