Evaluation Guidelines

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The use of neurodiagnostic studies in patients with altered consciousness with specific syndromes is outlined in Table 1:5 .

Neuroimaging. Neuroimaging studies should be selected based on the patient's history and the initial examination. If a structural lesion is suspected, an emergent CT scan should be obtained to guide therapy. Patients with





Fluid and Tissue Analysis

Neuropsychological Tests

Bilateral cortical dysfunction; confusion and delirium

Usually normal; may show atrophy; rarely bilateral chronic subdural hematoma or evidence of herpes simplex encephalitis; dural enhancement in meningitis, especially neoplastic meningitides

Diffuse slowing; often, frontally predominant intermittent rhythmic delta activity (FIRDA); in herpes simplex encephalitis, periodic lateralized epileptiform activity (PLEDS)

Blood or urine analyses may reveal etiology, CSF may show evidence of infection or neoplastic cells

In mild cases, difficulty with attention (e.g., trailmaking tests); in more severe cases, formal testing is not possible

Diencephalic dysfunction

Lesion(s) in or displacement of diencephalon; also displays mass displacing the diencephalon

Usually, diffuse slowing; rarely, FIRDA; in displacement syndromes, effect of the mass producing displacement (e.g., focal delta activity, loss of faster rhythms

Usually not helpful

Usually not obtained

Midbrain dysfunction

Lesion(s) in the midbrain or displacing it

Usually, diffuse slowing; alpha coma; evoked response testing may demonstrate failure of conduction above the lesion

Rarely, platelet or coagulation abnormalities

Usually not performed

Pontine dysfunction

Lesion(s) producing syndrome; thrombosis of basilar artery

EEG: usually normal; evoked responses usually normal

Rarely, platelet or coagulation abnormalities

Usually not performed

Medullary dysfunction

Lesion(s) producing dysfunction

EEG: normal; brain stem auditory and somatosensory evoked responses may show conduction abnormalities

Rarely, platelet or coagulation abnormalities

Usually not performed

Herniation syndromes

Lesion(s) producing herniation; appearance of perimesencephalie cistern

Findings related to etiology

Findings related to etiology

Usually not performed

Locked-in syndrome

Infarction of basis pontis

EEG and evoked potential studies: normal

Findings related to etiology

Usually not performed

Death by brain criteria

Absence of intracranial blood flow above the foramen magnum

EEG: electrocerebral silence; evoked potential studies may show peripheral components (e.g., wave I of brain stem auditory evoked response) but no central conduction

Absence of hypnosedative drugs

Not done

Psychogenic unresponsiveness




Helpful after patient "awakens"

CSF, Cerebrospinal fluid; EEG, electroencephalogram, FIRDA, frontally predomimant intermittent rhythmic delta activity; PLEDS, periodic lateralized eliptiform activity.

CSF, Cerebrospinal fluid; EEG, electroencephalogram, FIRDA, frontally predomimant intermittent rhythmic delta activity; PLEDS, periodic lateralized eliptiform activity.

bilateral hemispheric dysfunction do not usually benefit from emergent CT scanning. Although MR imaging is almost always superior in quality to CT, the pulse sequences currently employed may not detect all cases of acute intracranial bleeding. CT scanning is usually faster and more readily available in emergent circumstances.;:?! Positron emission tomography may be useful in the study of vegetative patients but is not widely available.

Electrophysiology. An EEG is indicated in most patients with altered consciousness at some point in their evaluation, usually after a structural lesion has been excluded, because the history and examination are inadequate to detect many cases of nonconvulsive status epilepticus. Patients in whom supratentorial structural lesions are present but are not adequate to explain the patient's state based on their location and size should also have an EEG performed.

Some EEG findings in patients with encephalopathy are characteristic; for example, frontally predominant rhythmic delta activity (FIRDA) and triphasic waves are common in metabolic disorders. An alpha coma pattern indicates either a midbrain lesion, anoxia, or hypnosedative drug overdose. In the setting of a hypnosedative drug overdose, the patient has a good prognosis for recovery. An unexpectedly normal EEG, with alpha blocking on passive eye opening and normal sleep-wake cycling, should alert the physician to the likelihood of psychogenic unresponsiveness. The EEG may also provide clues to otherwise unexpected diagnoses, such as subacute spongiform encephalopathy, which may come to medical attention in the guise of an acute encephalopathy. Evoked response studies are of limited value in these patients, and although abnormalities may be present (see T┬žbleJ-5 ), these studies seldom contribute diagnostically or therapeutically useful data in this population.1^]

Fluid and Tissue Analysis. Although the concept of routine tests has fallen from favor in laboratory medicine circles because of pressure from third-party payors, the patient with unexplained bilateral hemispheric dysfunction should indeed have a battery of screening tests to allow the physician to detect treatable etiologies rapidly. At a minimum, these tests should include a complete blood count with differential, platelet estimate or count, prothrombin time, partial thromboplastin time, serum osmolality, and serum and urinary screening for drugs of abuse.

If oral drug ingestion is considered a possibility, gastric aspiration for analysis of the contents and removal of remaining

unabsorbed drug is indicated. If the patient's airway protective reflexes are compromised, endotracheal intubation should be performed first. Induction of vomiting is no longer recommended in the emergency department because it may interfere with the use of activated charcoal to bind drugs. This substance may be used routinely unless acetaminophen ingestion is suspected, because it will interfere with the absorption of acetylcysteine as well.

Cerebrospinal Fluid. Cerebrospinal fluid (CSF) analysis is crucial in some conditions that alter consciousness (e.g., suspected meningitis) and is irrelevant in others. Thus, the decision to perform a lumbar puncture is based on the entire clinical picture. If bacterial meningitis is suspected and the physician believes that an imaging study should precede the lumbar puncture in these patients, then appropriate antibiotic therapy should be started before the patient is sent for the imaging study. Pneumococcal and meningococcal meningitides may be so rapidly fatal that even a brief delay in instituting antibiotic treatment should not occur.

Subarachnoid hemorrhage, either as a single event or as a repeated phenomenon, can also be diagnosed by lumbar puncture. The pattern of red blood cells and various pigments helps in establishing whether a patient with a known subarachnoid hemorrhage and a new onset of depressed level of consciousness has rebled or suffered another event like vasospasm.

In many instances of altered level of consciousness, ICP changes due to an intracranial mass lesion, ventricular obstruction, or other causes. As discussed in Chapter 26 , ICP reflects the net effect of static and dynamic forces affecting the intracranial contents. In the clinical context of decreased intracranial compliance, relatively small changes in volume have the potential to effect dangerous changes in pressure when the ICP is already elevated. Therefore, sudden and nonlinear rises in pressure are particularly important to control through ICP monitoring. Whereas in the normal brain, the perfusion pressure (mean arterial pressure minus mean ICP) must drop below 40 mm Hg before cerebral blood flow is impaired, in the damaged brain, the determinate pressure is less clear. Furthermore, often pressure increases are not distributed evenly throughout the cranium, and compartmentalized, very high pressure areas may not be accurately recorded by ICP monitoring. These features are particularly problematic in the instance of focal lesions with risks of herniations.

Neuropsychological Tests. Although most focal cortical abnormalities should be detected by the bedside neurological examination, formal neuropsychological testing may be valuable for detecting focal neurological dysfunction in patients who are thought to have diffuse disorders. This may be especially valuable in patients who present with an acute encephalopathy but do not improve, or in whom subsequent information indicates that a more chronic dementing process may be present.


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