Status Epilepticus
I. OVERVIEW
A. Definitions
Status epilepticus is defined as a condition in which seizures occur so frequently that the patient does not fully recover from one seizure before having another. Status epilepticus is also defined as a single prolonged seizure. A seizure lasting more than 5 minutes (especially a tonic-clonic seizure in an older child or adult) should be considered status epilepticus. Several types of status epilepticus exist, depending on seizure type: tonic-clonic (grand mal); simple partial (focal); complex partial (psychomotor, temporal lobe); and absence (petit mal). Tonic-clonic status epilepticus is the most common and most life-threatening type.
B. Epidemiology
The frequency of status epilepticus occurrences (all types) is 50 per 100,000 population per year or 125,000 occurrences per year in the United States. Frequency is highest in children and in adults older than 60 years. In both children and adults, approximately 80% of cases are of the tonic-clonic type. Approximately one third of cases fall into each of three groups: (a) first unprovoked seizure, (b) patients with well-established epilepsy, (c) acute new neurologic disease. Approximately 12% of all patients with newly diagnosed epilepsy are first seen with status epilepticus. The lifetime incidence of status epilepticus among patients with known seizure disorders is 1% to 4% and is highest in patients with symptomatic focal epilepsy.
Children have a high incidence of status epilepticus cases, with infants during the first year of life having the highest incidence. Up to 70% of children whose epilepsy begins before age 1 year will have an episode of status epilepticus after the diagnosis.
Four risk factors for status epilepticus in children have been identified: focal background electroencephalographic (EEG) abnormalities, partial seizures with secondary generalization, first seizure as status epilepticus, and generalized abnormalities on neuroimaging.
II. TONIC-CLONIC STATUS EPILEPTICUS
A. Clinical Presentation
Tonic-clonic status epilepticus generally follows a predictable sequence of events that can be described in three categories: motor, EEG, and systemic. In both human and animal studies, the phenomenology of these phases differs between early tonic-clonic status epilepticus (phase I) and late tonic-clonic status epilepticus (phase II). The transition from phase I to phase II usually occurs after 30 to 60 minutes.
1. Motor Events, Phase I
Phase I motor events consist of a tonic phase (muscles continuously contracted) followed by a clonic phase (alternate contraction and relaxation of muscles). The seizures are bilaterally synchronous at onset in 45% of patients; in the remainder, they are aversive (head, eyes, or both turned to one side) or focal at onset.
2. Motor Events, Phase II
As tonic-clonic status epilepticus continues, seizures often become shorter in duration and more restricted in distribution. Focal or lateralized motor activity may occur and does not necessarily imply focal pathology. Later, the motor activity may be reduced to brief muscle jerks (myoclonus) of the face, hands, or feet or nystagmoid jerking of the eyes. Finally, no motor activity may be seen at times when prominent paroxysmal activity is present on the EEG (electromechanical dissociation).
3. EEG Events
A progressive succession of five EEG patterns occurs in patients with tonic-clonic status epilepticus: (a) discrete clinical and EEG seizures with interictal slowing, (b) waxing and waning of ictal discharges, (c) continuous ictal discharge, (d) continuous ictal discharges punctuated by flat periods, and (e) periodic epileptiform discharges on a flat background. In later stages, electromechanical dissociation may be present. Considerable variability exists in the duration of each of these stages, and not all patients will progress through each stage.
4. Systemic Events
During the early phase of status epilepticus, an increase in blood pressure and glucose and lactate levels occurs. As the status continues, the blood pressure returns to normal or decreases, glucose decreases, hyperthermia may occur, and the patient is at risk for respiratory compromise. Additional events may include oral trauma, head trauma, aspiration pneumonia, orthopedic injuries (especially compression fractures of thoracic or lumbar vertebrae), myoglobinuria (caused by muscle breakdown during seizures), pulmonary edema, cardiac arrhythmias, myocardial infarction, dehydration, disseminated intravascular coagulation, leukocytosis, and cerebrospinal fluid (CSF) pleocytosis. These last two events, combined with fever, may spuriously suggest a central nervous system (CNS) infection.
5. Clinical Significance of Phase II Tonic-Clonic Status Epilepticus
Phase II status epilepticus has five clinically significant aspects. First, the initial presentation (to the treating physician) of tonic-clonic status epilepticus can be a comatose patient with or without myoclonic jerks if the patient has had preceding tonic-clonic seizures, or has had only a few tonic-clonic seizures after a severe cerebral insult. Second, brain damage during experimental models of tonic-clonic status epilepticus occurs only during phase II, and not during phase I. Third, phase II
tonic-clonic status epilepticus is more difficult to control with drugs than is phase I. Fourth, phase II tonic-clonic status epilepticus (periodic epileptiform discharges or continuous ictal discharge) is correlated with poor outcome. Fifth, these observations argue for aggressive therapy during phase I of tonic-clonic status epilepticus.
tonic-clonic status epilepticus is more difficult to control with drugs than is phase I. Fourth, phase II tonic-clonic status epilepticus (periodic epileptiform discharges or continuous ictal discharge) is correlated with poor outcome. Fifth, these observations argue for aggressive therapy during phase I of tonic-clonic status epilepticus.
B. Pathophysiology
Several factors appear to account for the prolongation of the epileptic state in tonic-clonic and partial status epilepticus: (a) changes in extracellular environment (e.g., increased potassium); (b) increase in excitatory α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and N-methyl-D-aspartate neurotransmission; (c) decrease in inhibitory (γ-aminobutyric acid) neurotransmission; (d) activation of voltage-gated calcium channels; and (e) reverberating seizure activity between, for example, hippocampal and parahippocampal structures. The longer the status persists, the harder it is to treat. A change in neuroreceptor function is found with a decreased response to benzodiazepines as the seizure progresses.
C. Prognosis
1. Mortality
The mortalities of status epilepticus in the pediatric, adult, and elderly populations are 2.5%, 14%, and 38%, respectively, with an overall rate of 22%. Death may result from the basic disease process causing status epilepticus, medical complications, or overmedication. The mortality related to prolonged seizures per se is 2% to 5%.
2. Causes of Status Epilepticus
Status epilepticus due to acute processes (metabolic disturbances, CNS infection, head trauma, stroke, hypoxia) is often difficult to control and is associated with higher mortality. Status epilepticus due to chronic processes (breakthrough seizures or discontinuing medication in patients with chronic epilepsy, old tumor, old stroke) often responds well to treatment. Table 12-1 lists causes of status epilepticus as a function of age.
3. Future Seizures
Patients who have a first episode of status epilepticus are at a substantial risk for future episodes of status epilepticus and the development of chronic epilepsy.
4. Brain Damage
Status epilepticus lasting 30 to 45 minutes can cause cerebral damage, especially to the hippocampus, in animals and humans. Other brain areas may be damaged as well. The damage appears to be caused more by glutamate-mediated excitotoxicity than by excessive metabolic demands of repetitive neuronal firing. Systemic stresses such as hypertension, hypoxia, and hyperpyrexia exacerbate the extent of neuronal injury in
animal models of status epilepticus and may have similar effects in humans.
animal models of status epilepticus and may have similar effects in humans.
Table 12-1. Causes of status epilepticus | |||||||||
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Virtually no studies systemically evaluated neuropsychological function before and after status epilepticus in an unselected human population. However, a substantial number of studies in both children and adults suggest that tonic-clonic or partial status epilepticus may be accompanied by permanent neurologic and cognitive sequelae in humans. On the basis of these studies and animal work, it is believed that prolonged tonic-clonic or complex partial seizures may cause brain damage or cognitive dysfunction in humans and should be prevented with vigorous therapy.
D. Treatment of Tonic-Clonic Status Epilepticus
The treatment plan for tonic-clonic status epilepticus given here is based on the plan of the Working Group on Status Epilepticus of the Epilepsy Foundation of America, published in 1993; it is summarized in Table 12-2. The only modifications are the inclusion of fosphenytoin and results from a Veterans Administration Cooperative study (23), which were not available when the plan was formulated.
1. Immediate Treatment
As with that in any unresponsive patient, initial management of status epilepticus includes the ABCs of life support (maintaining an airway, supporting breathing, maintaining circulation), gaining access to circulation, and when possible, identifying and treating the probable cause. Body temperature, blood pressure, the electrocardiogram, and respiratory function should be monitored closely as soon as status epilepticus is recognized. Status epilepticus should be managed in an emergency department or in an environment in which continuous skilled nursing care is available.
Table 12-2. A suggested timetable for the treatment of status epilepticus | ||||||||||||||||||||||||||
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A. AIRWAY AND OXYGENATION.
The head and mandible of the patient should be positioned to promote drainage of secretions, and if necessary, the airway should be suctioned to ensure patency. If it is feasible without undue force, an oral airway should be inserted. Oxygen should be administered by nasal cannula or mask and bag-valve-mask ventilator. If the need for respiratory assistance persists after the patient has been ventilated by bag-valve-mask, endotracheal intubation should be considered. If neuromuscular blockade is needed to facilitate intubation, use of a short-acting drug (e.g., vecuronium) enables the treating physician promptly to regain the ability to determine whether seizures are present clinically. Administering an antiepileptic drug is a top priority because managing the airway and assisting respiration are much easier after the convulsion is stopped.
B. GLUCOSE.
Although hypoglycemia is a rare cause of status epilepticus, it may complicate other predisposing conditions, such as alcoholism. In most cases of status epilepticus, several factors result in early hyperglycemia. This, in turn, promotes insulin secretion. Late in status epilepticus (usually after 2 hours), secondary hypoglycemia can occur. Consequently, all patients should have a prompt determination of blood glucose level. If hypoglycemia is documented or if obtaining a measurement of blood glucose is impossible, intravenous (i.v.) glucose should be administered through an indwelling venous catheter. In adults, an initial bolus injection of 50 mL of 50% glucose is used. In children, 25% glucose, 2 mL/kg, is administered. Thiamine, 100 mg i.v., should precede glucose administration in adults.
C. BLOOD PRESSURE.
During the first 30 to 45 minutes, status epilepticus usually produces hypertension; thereafter, blood pressure returns to normal or decreases below baseline values. Systolic blood pressure should be maintained at normal or highnormal levels during prolonged status, by using vasopressors if necessary.
D. INTRAVENOUS FLUIDS.
Overhydration should be avoided because it can exacerbate the cerebral edema usually present in tonic-clonic status epilepticus.
E. BLOOD WORK.
Blood should be drawn for a complete blood cell count; serum chemistry studies (including glucose, sodium, calcium, magnesium, and blood urea nitrogen determinations); and antiepileptic drug levels. Urine and blood samples should be obtained for toxicologic screening. In children, consideration should be given to metabolic testing if no other cause is determined. Adequate oxygenation should be confirmed by oximetry or periodic arterial blood gas determinations. In many patients
in status epilepticus, acidosis develops, but this usually resolves promptly when status epilepticus terminates. Bicarbonate therapy is usually unnecessary, but it should be considered when a patient has severe acidosis.
in status epilepticus, acidosis develops, but this usually resolves promptly when status epilepticus terminates. Bicarbonate therapy is usually unnecessary, but it should be considered when a patient has severe acidosis.
F. BODY TEMPERATURE.
Increased body temperature—sometimes to a striking degree—occurs in many patients with status epilepticus, primarily as a result of increased motor activity. Rectal temperature should be monitored frequently throughout treatment. Hyperthermia should be treated promptly with passive cooling because it may contribute to brain damage.
G. IDENTIFICATION AND TREATMENT OF PRECIPITATING FACTORS.
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