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Seizures represent stereotypic electroencephalographic (EEG) and behavioral paroxysms as a consequence of electrical neurological derangement. Seizures are usually described as focal or generalized motor convulsions. Other, nonconvulsive seizure types are common as well and require vigilant patient evaluation for optimal detection. Owing to the admission diagnoses and physiological derangements common to critically ill patients, the intensive care unit (ICU) hosts conditions appropriate for the manifestation of the entire spectrum of seizure disorders. Common etiologies of seizures in the ICU entail primary neurological pathology or secondary to critical illness and clinical management. Alterations in neurotransmitter sensitivity via up- or down regulation of receptors, a decrease in inhibition, or alterations in membrane pump functions may contribute to the high incidence of seizures in an ICU. Particularly prevalent as precipitants of seizures are hypoxia/ischemia, mass lesions, drug toxicity, and metabolic abnormalities. For optimal treatment, early diagnosis of the seizure type and its cause is important to ensure appropriate therapy. Most seizures and their recurrence are easily treated, and attention is focused on ascertaining the cause and correcting any medical abnormality. Convulsive status epilepticus, which represents the most feared seizure state, requires emergent treatment to prevent irreversible brain injury and severe metabolic disturbances. Treatment of seizures with anticonvulsants in an ICU is not without risks, and appropriate judgment and selection of therapeutic drugs are important.

Patients with hemorrhagic stroke are usually admitted for observation to an intensive care unit (ICU). A smaller percentage of patients with ischemic stroke are also admitted, as well as patients with cerebral venous thrombosis or those who have undergone carotid endarterectomy. All these patients are at risk for seizures. Those with hemorrhagic stroke are usually at two to three times higher risk than those with ischemic stroke, but several characteristics of the stroke modify the risk for having a seizure. In most cases an early seizure (within the first few days after the ictus) has a different significance from a late seizure (after the patient has been discharged from the ICU or the hospital). In addition, a significant role is played by the treatment offered to these patients, either medical, surgical, or endovascular. Despite an abundance of studies examining the incidence and characteristics of poststroke seizures, there are several questions still to be answered regarding the institution and duration of the appropriate treatment.

Seizures may occur in up to 22% of patients in the intensive care unit with severe traumatic brain injury. There is a relatively high risk of nonconvulsive seizures in this population. Seizures may exacerbate the injury process and disrupt both patient care and family coping. Therefore, seizures should be recognized quickly and treated promptly. The clinician should have a high index of suspicion for seizures, especially in patients with clearly defined risk factors for seizure development. Continuous electroencephalogram monitoring should be considered in patients who are considered to be at high risk of clinical or subclinical seizures. Seizure prophylaxis with antiepileptics is supported by the literature for the prevention of early seizures (defined as <7 d postinjury) but not for late seizures. Phenytoin and carbamazepine have been used in this setting, and both were efficacious in preventing early seizures. Phenytoin has several features that make it a best first-line agent. Anticonvulsants have not been found to reduce the incidence of developing late posttraumatic seizures, and, therefore, prolonged prophylaxis with antiepileptics is not currently supported.

Seizures are a common presentation of brain neoplasms. Both primary brain tumors and metastases can present with seizures, which are more commonly focal depending on the location and the pathology of the lesion. In general, more benign tumors have higher incidence of seizures than more malignant ones. These patients are admitted to an intensive care unit either for preoperative monitoring or in the postoperative period. They should be treated with antiepileptics if seizures are witnessed. Whether they should be prophylactically treated with antiepileptic medications if seizures have not occurred yet in the pre- and postoperative period, and for how long, are questions that remain to be answered. More recent data do not seem to support such prophylactic administration.

Seizures after cardiopulmonary arrest are a common problem in the intensive care unit, occurring in as many as one-third of these patients during their hospitalization. The etiology, treatment, and prognostic importance of seizures in this setting have not been well-delineated in the literature. Whether seizures exacerbate global hypoxic-ischemic brain injury in humans remains unclear, which raises uncertainty about how aggressively they should be treated. Some pathological data suggest that anoxic brain injury is worsened by generalized tonic-clonic (GTC) status epilepticus (SE). Especially when the prognosis remains uncertain, GTC SE should be treated in the conventional manner. Partial seizures and simple myoclonus are unlikely to exacerbate neuronal damage, and treatment probably should be reserved for seizures that are traumatic to family members or interfere with mechanical ventilation. Status myoclonus (SM) in hypoxic-ischemic coma is particularly troublesome because it can be highly refractory to conventional anticonvulsants and appears to portend an extremely poor prognosis, regardless of its management. Case series that report 100% mortality or vegetative state from this condition have involved only highly selected patient populations. Several cases have been reported of patients with good neurological outcomes despite SM in postanoxic coma. The most prudent course of action is to continue intensive management of patients with SM—including anticonvulsant therapy—and to rely on more precise means of prognostication (clinical exam, electroencephalography, and somatosensory evoked potential) to inform the decision to withdraw supportive care. The decision to use anesthetic agents and paralytics in this setting must be individualized.

Hepatorenal failure and endocrine disease are associated with seizures. Seizures arise either as a direct result of the organ failure or as a result of a secondary metabolic disturbance, including toxins arising from the disease process or changes in serum electrolytes. Correction of electrolyte abnormalities or medical management of the underlying disease process will often prevent further seizures. Organ failure and endocrine abnormalities are commonly seen in the critically ill population, and these patients are more prone to seizures. Organ failure can influence the treatment of both new-onset and pre-existing seizure disorders by altering the pharmacokinetics of major anticonvulsants. Alternatively, anticonvulsants can precipitate organ failure. Therefore pharmacotherapy of seizures in these settings should be undertaken cautiously.

Seizures are a nonspecific neurological manifestation of cerebral dysfunction and are not indicative of any particular disease processes or pathology. Thus, the evaluation and treatment of seizures in transplant patients generally follows the same clinical approach used for other patients. A seizure in a transplant patient is commonly unanticipated and entirely unexplained. The effects can be substantial, with aspiration, loss of vascular catheters, and tissue trauma. Patients undergoing organ transplantation are at risk for seizures for multiple reasons, and although much of the neurological and transplantation literature reports on the incidence of seizures according to the particular organ transplanted (Table 1), there are many similarities (e.g., immunosuppression drugs). This chapter concentrates on organ transplantation as a whole.

The association between seizures and blood pressure elevation remains a common medical emergency encountered in the setting of an intensive care unit. Syndromes such as preeclampsia or eclampsia, hypertensive encephalopathy, and posterior leukoencephalopathy commonly present with seizures. The primary treatment goal is to reduce the arterial blood pressure. In most cases, seizure control is thus achieved, but unique medications, such as magnesium sulfate, may be needed. Fortunately the pathophysiologic mechanism leading to seizures is reversible in most cases that are treated immediately and aggressively. Delayed treatment may result in irreversible brain injury or increased mother or fetus mortality.

Effective treatment of seizures associated with central nervous system (CNS) infection and inflammation depends on rapid diagnosis and early attainment of bactericidal activity in the cerebrospinal fluid with appropriate antimicrobial agents, or appropriate management of vasculitis-induced cerebral complications. Despite the rarity of these disorders, there is nothing specific regarding the management in the intensive care unit of seizures in these situations, except for a high suspicion by the medical staff. Improvement in long-term neurologic outcome depends on both therapy of the infectious/inflammatory process and the intensive care multisystem monitoring commonly warranted in this patient population. The primary goal of preserving CNS function is shared by the neurologist and the intensivist, making a multidisciplinary approach essential.

Electrolyte disturbances in the ICU are extremely common. The electrolyte disorder most commonly associated with seizure is hyponatremia, although extremely low Mg, phosphate, and both very low and very high Ca values can cause seizures. Critical care physicians must be vigilant to suspect and identify electrolyte disturbances in their patients, because a growing amount of information suggests that they are a marker, and potentially a cause, of poor prognosis. Electrolyte disturbance should never be accepted as the etiology of a seizure until a thorough investigation has been undertaken.