1 Sudden Deterioration in Neurologic Status
Patients admitted to the intensive care unit (ICU) with critical illness or injury are at risk for neurologic complications.1–5 A sudden or unexpected change in the neurologic condition of a critically ill patient often heralds a complication that may cause direct injury to the central nervous system (CNS). Alternatively, such changes may simply be neurologic manifestations of the underlying critical illness or treatment that necessitated ICU admission (e.g., sepsis). These complications can occur in patients admitted to the ICU without neurologic disease and in those admitted for management of primary CNS problems (e.g., stroke). Neurologic complications also can occur as a result of invasive procedures and therapeutic interventions performed. Commonly, recognition of neurologic complications is delayed or missed entirely because ICU treatments (e.g., intubation, drugs) interfere with the physical examination or confound the clinical picture. In other cases, neurologic complications are not recognized because of a lack of sensitive methods to detect the problem (e.g., delirium). Morbidity and mortality are increased among patients who develop neurologic complications; therefore, the intensivist must be vigilant in evaluating all critically ill patients for changes in neurologic status.
Despite the importance of neurologic complications of critical illness, few studies have specifically assessed their incidence and impact on outcome among ICU patients. Available data are limited to medical ICU patients; data regarding neurologic complications in general surgical and other specialty ICU populations must be extracted from other sources. In studies of medical ICU patients, the incidence of neurologic complications is 12.3% to 33%.1,2 Patients who develop neurologic complications have increased morbidity, mortality, and ICU length of stay. Sepsis is the most common problem associated with development of neurologic complications (sepsis-associated encephalopathy). In addition to encephalopathy, other common neurologic complications associated with critical illness include seizures and stroke. As the complexity of ICU care has increased, so has the risk of neurologic complications. Neuromuscular disorders are now recognized as a major source of morbidity in severely ill patients.6 Recognized neurologic complications occurring in selected medical, surgical, and neurologic ICU populations are shown in Table 1-1.7–41
TABLE1-1 Neurologic Complications in Selected Specialty Populations
| Medical | |
| Bone marrow transplantation7,8 | CNS infection, stroke, subdural hematoma, brainstem ischemia, hyperammonemia, Wernicke encephalopathy |
| Cancer9 | Stroke, intracranial hemorrhage, CNS infection |
| Fulminant hepatic failure10 | Encephalopathy, coma, brain edema, increased ICP |
| HIV/AIDS11,12 | Opportunistic CNS infection, stroke, vasculitis, delirium, seizures, progressive multifocal leukoencephalopathy |
| Pregnancy13,14 | Seizures, ischemic stroke, cerebral vasospasm, intracranial hemorrhage, cerebral venous thrombosis, hypertensive encephalopathy, pituitary apoplexy |
| Surgical | |
| Cardiac surgery15–19 | Stroke, delirium, brachial plexus injury, phrenic nerve injury |
| Vascular surgery20,21: | |
| Carotid | Stroke, cranial nerve injuries (recurrent laryngeal, glossopharyngeal, hypoglossal, facial), seizures |
| Aortic | Stroke, paraplegia |
| Peripheral | Delirium |
| Transplantation10,22–25: | |
| Heart | Stroke |
| Liver | Encephalopathy, seizures, opportunistic CNS infection, intracranial hemorrhage, Guillain-Barré syndrome, central pontine myelinolysis |
| Renal | Stroke, opportunistic CNS infection, femoral neuropathy |
| Urologic surgery (TURP)26 | Seizures and coma (hyponatremia) |
| Otolaryngologic surgery27,28 | Recurrent laryngeal nerve injury, stroke, delirium |
| Orthopedic surgery29: | |
| Spine | Myelopathy, radiculopathy, epidural abscess, meningitis |
| Knee and hip replacement | Delirium (fat embolism) |
| Long-bone fracture/nailing | Delirium (fat embolism) |
| Neurologic | |
| Stroke30–34 | Stroke progression or extension, reocclusion after thrombolysis, bleeding, seizures, delirium, brain edema, herniation |
| Intracranial surgery35 | Bleeding, edema, seizures, CNS infection |
| Subarachnoid hemorrhage32,36–38 | Rebleeding, vasospasm, hydrocephalus, seizures |
| Traumatic brain injury32,39,40 | Intracranial hypertension, bleeding, seizures, stroke (cerebrovascular injury), CNS infection |
| Cervical spinal cord injury41 | Ascension of injury, stroke (vertebral artery injury) |
CNS, central nervous system; HIV/AIDS, human immunodeficiency virus/acquired immunodeficiency syndrome; ICP, intracranial pressure; TURP, transurethral prostatic resection.
Impairment in Consciousness
Global changes in CNS function, best described in terms of impairment in consciousness, are generally referred to as encephalopathy or altered mental status. An acute change in the level of consciousness undoubtedly is the most common neurologic complication that occurs after ICU admission. Consciousness is defined as a state of awareness (arousal or wakefulness) and the ability to respond appropriately to changes in environment.42 For consciousness to be impaired, global hemispheric dysfunction or dysfunction of the brainstem reticular activating system must be present.43 Altered consciousness may result in a sleeplike state (coma) or a state characterized by confusion and agitation (delirium). States of acutely altered consciousness seen in the critically ill are listed in Table 1-2.
| State | Description |
|---|---|
| Coma | Closed eyes, sleeplike state with no response to external stimuli (pain) |
| Stupor | Responsive only to vigorous or painful stimuli |
| Lethargy | Drowsy, arouses easily and appropriately to stimuli |
| Delirium | Acute state of confusion with or without behavioral disturbance |
| Catatonia | Eyes open, unblinking, unresponsive |
When an acute change in consciousness is noted, the patient should be evaluated keeping in mind the patient’s age, presence or absence of coexisting organ system dysfunction, metabolic status and medication list, and presence or absence of infection. In patients with a primary CNS disorder, deterioration in the level of consciousness (e.g., from stupor to coma) frequently represents the development of brain edema, increasing intracranial pressure, new or worsening intracranial hemorrhage, hydrocephalus, CNS infection, or cerebral vasospasm. In patients without a primary CNS diagnosis, an acute change in consciousness is often due to the development of infectious complications (i.e., sepsis-associated encephalopathy), drug toxicities, or the development or exacerbation of organ system failure. Nonconvulsive status epilepticus is increasingly being recognized as a cause of impaired consciousness in critically ill patients (Box 1-1).44–53
Box 1-1
General Causes of Acutely Impaired Consciousness in the Critically Ill
CNS, central nervous system.
States of altered consciousness manifesting as impairment in wakefulness or arousal (i.e., coma and stupor) and their causes are well defined.42,43,54,55 Much confusion remains, however, regarding the diagnosis and management of delirium, perhaps the most common state of impaired CNS functioning in critically ill patients at large. When dedicated instruments are used, delirium can be diagnosed in more than 80% of critically ill patients, making this condition the most common neurologic complication of critical illness.56–58 Much of the difficulty in establishing the diagnosis of delirium stems from the belief that delirium is a state characterized mainly by confusion and agitation and that such states are expected consequences of the unique environmental factors and sleep deprivation that characterize the ICU experience. Terms previously used to describe delirium in critically ill patients include ICU psychosis, acute confusional state, encephalopathy, and postoperative psychosis. It is now recognized that ICU psychosis is a misnomer; delirium is a more accurate term.59
Currently accepted criteria for the diagnosis of delirium include abrupt onset of impaired consciousness, disturbed cognitive function, fluctuating course, and presence of a medical condition that could impair brain function.60 Subtypes of delirium include hyperactive (agitated) delirium and the more common hypoactive or quiet delirium.58 Impaired consciousness may be apparent as a reduction in awareness, psychomotor retardation, agitation, or impairment in attention (increased distractibility or vigilance). Cognitive impairment can include disorientation, impaired memory, and perceptual aberrations (hallucinations or illusions).61 Autonomic hyperactivity and sleep disturbances may be features of delirium in some patients (e.g., those with drug withdrawal syndromes, delirium tremens). Delirium in critically ill patients is associated with increased morbidity, mortality, and ICU length of stay.62–64
