Delirious Patients

Diagnosis

The essential features of delirium, according to the DSM-5, are a disturbance of attention and awareness accompanied by cognitive deficits that develop over a short period of time and tend to wax and wane over the course of the day in the setting of evidence that these deficits are the direct physiologic consequences of a physiologic condition (including medical illness, substance intoxication or withdrawal, and toxin exposure). Disturbance of the sleep–wake cycle is also common, sometimes with nocturnal worsening (sundowning) or even by a complete reversal of the night–day cycle, though, despite previous postulation and ongoing hospital folklore, sleep disturbance alone does not cause delirium. Similarly, the term ICU psychosis persists in the medical lexicon; this is an unfortunate and lazy misnomer because it assigns the environment of the ICU as the cause of delirium, effectively allowing the clinician to shrug off any burden of having to explore this syndrome further, and it inaccurately limits the symptomatology of delirium to psychosis. Despite wide variation in the presentation of the delirious patient, the hallmarks of delirium, although perhaps less immediately apparent, remain quite consistent from case to case.

Impaired attention has long been regarded as the main deficit of delirium. This inattention (along with an acute onset, waxing and waning course, and overall disturbance of consciousness) forms the core features of delirium, whereas other related symptoms, such as withdrawn affect, agitation, hallucinations, and paranoia, serve as a frame that can sometimes be so prominent as to distract from the picture itself.

Psychotic symptoms (such as visual or auditory hallucinations and delusions) are common among patients with delirium. Sometimes the psychiatric symptoms are so bizarre or so offensive (e.g., an enraged and paranoid patient shouts that pornographic movies are being made in the ICU) that diagnostic efforts are distracted. The delirium-inducing hypoglycemia of a man with diabetes can be missed in the Emergency Department (ED) if the accompanying behavior is threatening, uncooperative, and resembling that of an intoxicated person.

Although agitation can distract clinicians from making an accurate diagnosis of delirium, disruptive behavior alone will almost certainly garner some attention. The hypoactive presentation of delirium is more insidious, because the patient is often thought to be depressed or anxious because of the medical illness. Studies of quietly delirious patients show the experience to be as disturbing as the agitated variant; quiet delirium is still a harbinger of serious medical pathology.

The core similarities found in cases of delirium have led to postulation of a final common neurologic pathway for its symptoms. Current understanding of the neurotransmitter imbalance involved in delirium is one of hyperdopaminergia and hypocholinergia. The ascending reticular activating system (RAS) and its bilateral thalamic projections regulate alertness, with neocortical and limbic inputs to this system controlling attention. Because acetylcholine is the primary neurotransmitter of the RAS, medications with anticholinergic activity can interfere with its function, resulting in the deficits in alertness and attention that are the heralds of delirium. Similarly, it is thought that loss of cholinergic neuronal activity in the elderly (e.g., resulting from microvascular disease or atrophy) is the basis for their heightened risk of delirium. Release of endogenous dopamine due to oxidative stress is thought to be responsible for the perceptual disturbances and paranoia that so often lead to mislabeling the delirious patient “psychotic.” As discussed later, cholinergic agents (e.g., physostigmine) and dopamine blockers (e.g., haloperidol) have proved efficacious in managing delirium.

Early detection of changes in cognition can be key to timely identification and treatment of delirium (and perhaps of a heretofore undiagnosed somatic illness responsible for the delirium). Unfortunately, studies have revealed that non-psychiatrist physicians are quite unreliable in their ability to identify delirium accurately, and most patients referred to psychiatric consultation services with purported depression are ultimately found to have delirium. Because consultation psychiatrists cannot perform repeated examinations on all patients admitted to the general hospital (even on those at high risk for delirium), a number of screening protocols designed to be administered serially by nursing staff have been developed and validated for use. Some of the most commonly used of these scales are summarized in Table 10-1 .

Differential Diagnosis

As useful as screening protocols may be, treatment relies on a careful diagnostic evaluation; there is no substitute for a systematic search for the specific cause of delirium. The temporal relationship to clinical events often gives the best clues to potential causes. For example, a patient who extubated himself was almost certainly in trouble before self-extubation. When did his mental state actually change? Nursing notes should be studied to help discern the first indication of an abnormality (e.g., restlessness, mild confusion, anxiety). If a time of onset can be established as a marker, other events can be examined for a possible causal relationship to the change in mental state. Vital signs can reveal periods of hypotension or fever. The highest temperature recorded will also be key. Operative procedures and the use of anesthetics can also induce a sustained period of hypotension or reveal unusually large blood loss that requires replacement. Laboratory values should be scanned for abnormalities that could be related to an encephalopathic state. Initiation or discontinuation of a drug, the onset of fever or hypotension, or the acute worsening of renal function, if in proximity to the time of mental status changes, become likely culprits.

Without a convincing temporal connection, causes of delirium should be investigated based on their likelihood in the unique clinical situation of the patient. In critical care settings, there are several (life-threatening) states that the clinician can consider routinely. These are states in which intervention needs to be especially prompt because failure to make the diagnosis may result in permanent central nervous system (CNS) damage. These conditions are Wernicke's disease, hypoxia, hypoglycemia, hypertensive encephalopathy, hyper- or hypothermia, intracerebral hemorrhage, meningitis or encephalitis, poisoning (exogenous or iatrogenic), and status epilepticus. These conditions are usefully recalled by the mnemonic device “WHHHHIMPS” ( Table 10-2 ). Other less urgent but still acute conditions that require intervention include intracranial bleeds, sepsis, hepatic or renal failure, thyrotoxicosis or myxedema, delirium tremens, and complex partial seizures. If these conditions are not already ruled out, they are easy to verify. A broad review of conditions commonly associated with delirium is provided by the mnemonic “I WATCH DEATH” ( Table 10-3 ).

Bacteremia commonly clouds a patient's mental state. In prospectively studied seriously ill hospitalized patients, delirium was commonly correlated with bacteremia. In that study, the mortality of septic patients with delirium was higher than that in septic patients with a normal mental status. In the elderly, regardless of the setting, the onset of confusion should trigger concern about infection. Urinary tract infections (UTIs) and pneumonias are among the most common infections in older patients, and when bacteremia is associated with a UTI, confusion is the presenting feature nearly one-third (30%) of the time. Once a consultant has eliminated these common conditions as possible causes of a patient's disturbed brain function, there is time enough for a more systematic approach to the differential diagnosis. While an old medical adage tells us to think of horses when we hear hoofbeats, it behooves the psychiatric consultant to maintain an awareness of the zebras and unicorns that might have evaded detection. A comprehensive differential diagnosis, similar to the one compiled by Ludwig (expanded in Table 10-4 ) is recommended. A quick review of this list is warranted even when the consultant is relatively sure of the diagnosis.

Prior medical records, no matter how lengthy, cannot be overlooked without risk. Some patients have had psychiatric consultations for similar difficulties on prior admissions. Others, in the absence of psychiatric consultations, have caused considerable trouble for their caregivers. Similar to a patient's psychiatric history, the family psychiatric history can help make a diagnosis, especially if a major mood or anxiety disorder, alcoholism, schizophrenia, or epilepsy is present.

Examination of current and past medications is essential because pharmacologic agents (in therapeutic doses, in overdose, or with withdrawal) can produce psychiatric symptoms. These medications must be routinely reviewed, especially in patients whose drugs have been stopped because of surgery or hospitalization or whose drug orders have not been reconciled during transfer between services or institutions. Of all causes of an altered mental status, use of and withdrawal from drugs are probably the most common. Some, such as lidocaine, are quite predictable in their ability to cause encephalopathy; the frequency and severity of symptoms are dose-related. Other agents usually cause delirium only in someone whose brain is already vulnerable, as in a patient with a dementia. Table 10-5 lists some drugs used in clinical practice that have been associated with delirium.

The number of drugs that can be involved either directly or indirectly (e.g., because of drug interactions) is numerous. Fortunately, there are an array of resources (including websites and smartphone applications) that easily allow for identification of these issues. Once identified, the usual treatment is to stop the offending drug or to reduce the dosage; however, at times this is not possible. Elderly patients, those with impairments of metabolism (e.g., hepatic or renal failure), and those with neurodevelopmental disorders or a history of significant head injury are more susceptible to the toxic actions of many of these drugs.

Psychiatric symptoms in medical illness can have other causes. Besides the abnormalities that can arise from the effect of the patient's medical illness (or its treatment) on the CNS (e.g., the abnormalities produced by systemic lupus erythematosus or high-dose steroids), the disturbance may be the effect of the medical illness on the patient's mind (the subjective CNS), as in the patient who thinks he or she is “done for” after a myocardial infarction, quits, and withdraws into hopelessness. The disturbance can also arise from the mind, as a conversion symptom or as malingering about pain to get more narcotics. Finally, the abnormality may be the result of interactions between the sick patient and his or her environment or family (e.g., the patient who is without complaint until the family arrives, at which time the patient promptly looks acutely distressed and begins to whimper continuously). Nurses are commonly aware of these sorts of abnormalities, although they may refrain from documenting them in the medical record.