Perspective

Altered mental status is a spectrum of disease ranging from sleepiness and confusion to frank coma. Approximately 3% of patients arrive at the emergency department (ED) in a altered state.

Epidemiology

Roughly 85% of cases of altered mental status are caused by metabolic or systemic derangements, whereas 15% are caused by structural lesions. Once the ABCs (airway, breathing, and circulation) have been controlled and the patient stabilized, it is the role of the emergency physician (EP) to quickly distinguish structural from metabolic and systemic causes.

Pathophysiology

Consciousness is collectively made up of arousal and cognition. Arousal is defined as the awareness of self and the surroundings. The neuroanatomic structure primarily responsible for arousal is the ascending reticular activating system, which is located in the dorsal part of the brainstem. It controls the input of somatic and sensory stimuli to the cerebral cortex and functions to initiate arousal from sleep. Cognition is the combination of orientation (accurate perception of what is experienced), judgment (the ability to process input data to generate more meaningful information), and memory (the ability to store and retrieve information). The brain’s cognition centers are located primarily in the cerebral cortex.

Coma can be caused by damage to the brainstem (Fig. 94.1), the cerebral cortex, or both. These structures are vulnerable to toxins, metabolic derangements, and mechanical injury. Localized, unilateral lesions in the cerebral cortex do not usually induce altered mental status or coma, even with other cognitive functions being impaired. However, if both cerebral hemispheres are affected, altered mental status or coma can occur, depending on the size of the insult and its speed of progression. The ascending reticular activating system can also be vulnerable to small, focal lesions in the brainstem, which can result in coma.^1,2

Fig. 94.1 Cerebral insults leading to a depressed level of consciousness.

A, Ascending reticular activating system; B, bilateral cerebral cortex.

Presenting Signs and Symptoms

The chief complaints of patients and their family members are highly variable along the spectrum of altered mental status. Patients may report increased sleepiness or periods of confusion and disorientation. They may have trouble concentrating or maintaining focus on tasks that were previously performed without difficulty. Family members may describe the patient as being less interactive or more difficult to arouse from sleep.

Regardless of the circumstance, the EP will frequently need to use alternative sources of information to answer key historical questions that may alter the breadth and speed of the diagnostic work-up undertaken. Common sources of information include family members, neighbors, prehospital personnel, law enforcement, and nursing home staff.³ They may know of preceding symptoms such as headache, nausea, vomiting, or fever. It is important to determine the rate of symptom onset and whether the patient had any history of trauma, exposure to drugs or toxins, or new medications or change in dosage. Family members usually have some knowledge regarding the patient’s past medical history. Additionally, previous medical records should be reviewed whenever possible to confirm or augment the information provided. If the patient’s historical baseline mental status cannot be established, the current findings must be assumed to be an acute change.⁴

The age of the patient can be a key historical tool that may focus the physician on the most probable cause of the patient’s symptoms (Box 94.1).

In infants, infectious causes of altered mental status are most common; however, nonaccidental trauma and metabolic derangements from inborn errors of metabolism are also possible causes.⁵ Toxic ingestions are commonly seen in young children. Adolescents and young adults are often seen in the ED after recreational drug use. The elderly are particularly susceptible to infectious causes and to disorders related to changes in medications or drug doses, use of over-the-counter medications, and alterations in their living environment. Psychiatric illness should be considered in the adolescent through elderly population and must be distinguished from medical illness as a cause of the patient’s symptoms.

As with all patients, specific attention should first be paid to assessment of the ABCs and specific vital signs. Alterations in respiratory patterns such as hyperventilation, Kussmaul or Cheyne-Stokes breathing, agonal breathing, or apnea should be noted and may suggest toxic or metabolic derangements or primary central nervous system abnormalities. Marked hypotension or hypertension should be addressed immediately even if the underlying cause is unknown. Bradycardia may be the result of increased intracranial pressure as seen in the Cushing response and suggests a state of hypoperfusion. Tachycardia may also result in hypoperfusion and can be the result of toxic, metabolic, or primary cardiac causes. Assessment of temperature is crucial because both hypothermia and hyperthermia can cause altered mental status from infectious, structural (Box 94.2), environmental exposure, or toxic or metabolic causes (Box 94.3).