Disorders of consciousness may be divided into processes that affect either arousal or content of consciousness, or a combination of both. Arousal behaviors include wakefulness and basic alerting. Anatomically, neurons responsible for these arousal functions reside in the reticular activating system, a collection of neurons scattered through the midbrain, pons, and medulla. The neuronal structures responsible for the content of consciousness reside in the cerebral cortex. Content of consciousness includes self-awareness, language, reasoning, spatial relationship integration, emotions, and the myriad complex integration processes that make us human. One simplistic model holds that dementia is failure of the content portions of consciousness with relatively preserved alerting functions. Delirium is arousal system dysfunction with the content of consciousness affected as well. Coma is failure of both arousal and content functions. Psychiatric disorders and altered mental states may share features such as hallucinations or delusion. Some distinctions between the different states are summarized in Table 168-1.

Mental status is the clinical state of emotional and intellectual functioning of the individual. The mental status evaluation may be divided into six areas (Table 168-2). Testing the mental status is done both formally and informally in patient evaluation by emergency physicians.¹ Assessment of higher mental or cognitive functions requires specific tests. Screening tests are described in the Diagnosis subsections under Delirium, Dementia, and Coma.

INTRODUCTION

Delirium, acute confusional state, acute cognitive impairment, acute encephalopathy, altered mental status, and other synonyms all refer to a transient disorder with impairment of attention and cognition. The patient has difficulty focusing, shifting, or sustaining attention. Confusion may fluctuate (Table 168-1).

The incidence of delirium in ED populations is not clear. It is estimated that 10% to 25% of elderly hospitalized patients have delirium at the time of admission.^2,3 The literature suggests that up to one quarter of all ED patients aged 70 years or older have impaired mental status or delirium and contends that routine evaluation is not satisfactory to identify many of these patients.^4,5

PATHOPHYSIOLOGY

Pathologic mechanisms producing delirium are complex and are thought to involve widespread neuronal or neurotransmitter dysfunction. There are four general causes⁶:

1. 
   

   Primary intracranial disease

   
   
2. 
   

   Systemic diseases secondarily affecting the CNS

   
   
3. 
   

   Exogenous toxins

   
   
4. 
   

   Drug withdrawal

CLINICAL FEATURES

Delirium or acute confusional state generally develops over days. Attention, perception, thinking, and memory are all altered. Alertness is reduced as manifested by difficulty maintaining attention and focusing concentration. The patient may appear quite awake, but attention is impaired. Activity levels may be either increased or decreased. The patient may fluctuate rapidly between hypoactive and hyperactive states. Symptoms may be intermittent, and it is not unusual for different caregivers to witness completely different behaviors within a brief time span. The sleep-wake cycles are often disrupted, with increased somnolence during the day and agitation at night, or “sundowning.” Tremor, asterixis, tachycardia, sweating, hypertension, and emotional outbursts may be present. Hallucinations tend to be visual, although auditory hallucinations can also occur.^2,3,7

DIAGNOSIS

Both historical and physical examination findings indicating delirium are necessary to confirm the diagnosis. Obtaining a history from caregivers, spouse, or other family members is the primary method for diagnosing delirium.^2,3,7 The acute onset of attention deficits and cognitive abnormalities fluctuating in severity throughout the day and worsening at night is virtually diagnostic of delirium. Examine medication history, including over-the-counter medications taken and prescribed medications, in detail. Check for drug interactions. Assess for an underlying process, such as pneumonia or urinary tract infection. Ancillary testing should include serum electrolyte levels, hepatic and renal studies, urinalysis, CBC, and a chest radiograph. Order a head CT if a mass lesion such as subdural hematoma is suspected; follow this by performing a lumbar puncture if meningitis or subarachnoid hemorrhage is considered.

One key tool for detecting delirium is the mental status examination and other cognitive screening instruments.^8,9,10,11,12 These tests are valuable in directing the physician to study aspects of attention and memory that might not otherwise be formally tested. Parts of the Mini-Mental State Examination are sometimes used in the ED.^8,9,10 The complete test takes 7 to 10 minutes to administer, but copyright restrictions limit reproduction and use.¹¹ Age, education, chronic cognitive impairment, and verbal abilities all may affect scores. The Mini-Mental State Examination does not detect mild impairment. The median positive and negative likelihood ratios for the test are 6.3 and 0.19, respectively.¹¹ Several other shorter evaluation tools have been proposed. ^9,10,11,12 The Quick Confusion Scale has been tested in ED patients, yields scores that correlate well with those on the Mini-Mental State Examination (r = 0.61 in one study¹⁰ and 0.783 in another⁹), and takes <3 minutes to administer. The patient does not need to read, write, or draw to complete the test¹⁰ (Table 168-3).

Depression may resemble hypoactive delirium, with withdrawal, slowed speech, and poor results on cognitive testing present in both conditions. However, rapid fluctuation of symptoms is common in delirium but generally absent in depression. In addition, clouding of consciousness is absent in patients with depression. Patients with depression are oriented and able to perform commands.

An unusual cause of confusional state, but one that is suspected to be underrecognized, is nonconvulsive status epilepticus, or complex partial status epilepticus. This twilight state may persist for hours or even months. Suspicion and electroencephalography are required for recognition.¹⁰ (See chapter 171, Seizures, for further discussion of nonconvulsive status epilepticus.)

TREATMENT

Direct treatment at the underlying cause. Common medical causes of delirium are listed in Table 168-4. Multiple causes may be present in a given patient.

Environmental manipulations such as adequate lighting, psychosocial support, and mobilization may be helpful in enhancing the patient’s ability to interpret the surroundings correctly.^2,6,7 Sedation may be needed. Haloperidol is a frequent initial choice at a dose of 5 to 10 milligrams PO, IM, or IV with reduced dosing of 1 to 2 milligrams in the elderly. Repeat at 20- to 30-minute intervals as needed. Benzodiazepines such as lorazepam, 0.5 to 2.0 milligrams PO, IM, or IV, may be used in combination with haloperidol in doses of 1 to 2 milligrams, with the dose varying widely depending on the age and size of the patient and the degree of agitation. Chapter 287, Acute Agitation, provides further discussion on management of agitation.

DISPOSITION AND FOLLOW-UP

Admit the patient into the hospital for further treatment and additional diagnostic testing unless a readily reversible cause for the acute mental status change is discovered and treatment initiated. This decision is individualized with consideration of patient characteristics, the resources in the home or healthcare facility, and the patient’s safety.