period Subtherapeutic antiepileptic drug levels are one of the most common causes of seizures in this population The presence of fever may indicate that a febrile seizure has occurred or, if normal consciousness is not regained, that the patient has contracted a CNS infection such as meningitis or encephalitis (see Chapters 94 Infectious Disease Emergencies and 97 Neurologic Emergencies ) The new onset of afebrile generalized seizures requires a more thorough evaluation, as detailed in Chapter 72 Seizures Infection Coma-inducing infections of the CNS may involve large areas of the brain and surrounding structures, as in meningitis or encephalitis, or they may be confined to a smaller region, as in the case of cerebral abscess or empyema (see Chapter 94 Infectious Disease Emergencies ) The incidence of bacterial meningitis due to Haemophilus influenzae , Streptococcus pneumoniae and Neisseria meningitidis has diminished among vaccinated children, but these infections still occur in unvaccinated and undervaccinated patients, and in the immunocompromised Lyme disease is now present throughout the United States, and is a common cause of meningitis Meningitis may also be caused by viral (enteroviruses, herpes), fungal (Candida, Cryptococcus ), mycobacterial (tuberculosis), and parasitic (cysticercosis) organisms These nonbacterial infections usually have a slower onset of symptoms Encephalitis, or inflammation of brain parenchyma, may also involve the meninges (see Chapter 94 Infectious Disease Emergencies ) It occurs most commonly as a result of viral infection or immunologic mechanisms Mumps and measles were common causes before immunizations against these diseases, and they still occur in unimmunized individuals or in individuals in whom immunity has waned Varicella encephalitis occurs to days after the onset of rash The incidence of arthropod-borne encephalitides varies by geographic location but usually peaks in late summer and early fall The herpes simplex virus (HSV) remains the most common devastating cause of encephalitis, causing death or permanent neurologic sequelae in the majority of patients Beyond the neonatal period, HSV affects the temporal lobes most severely, leading to seizures and parenchymal swelling, which can cause uncal herniation Focal CNS infections include brain abscesses, subdural empyemas, and epidural abscesses (see Chapter 94 Infectious Disease Emergencies ) Brain abscesses occur most often in patients with chronic sinusitis, chronic ear infection, dental infection, endocarditis, or uncorrected cyanotic congenital heart disease Subdural empyema also occurs as a result of chronic ear or sinus infection, but it is most commonly seen as a sequela of bacterial meningitis Cranial epidural abscess is rare, but most cases occur from extension of sinusitis, otitis, orbital cellulitis, or calvarial osteomyelitis Neoplasms Alterations in consciousness as a result of intracranial neoplasms (see Chapter 98 Oncologic Emergencies ) may be caused by seizure, hemorrhage, increases in ICP caused by interruption of CSF flow, or direct invasion of the brainstem by the malignancy The location of the tumor determines additional symptoms: Ataxia and vomiting result from infratentorial lesions versus seizures, hemiparesis, and speech or intellectual difficulties resulting from supratentorial ones Hydrocephalus caused by tumor growth most commonly presents with headache (especially morning headache), decreased activity or lethargy, and vomiting Vascular Coma of cerebrovascular origin is caused by interruption of cerebral blood flow (stroke) as a result of hemorrhage, thrombosis, or embolism (see Chapter 97 Neurologic Emergencies ) Hemorrhage can be nontraumatic, stemming from abnormal congenital vascular structures such as arteriovenous malformations (AVM), aneurysms, or cavernous hemangiomas Rupture of an AVM is the most common cause of spontaneous intracranial bleeding among pediatric patients The hemorrhage is arterial in origin and located within the parenchyma, but it can rupture into a ventricle or the subarachnoid space Aneurysm rupture is less common in children and is unusual in that repetitive episodes of bleeding may occur (“sentinel bleeds”), with rising morbidity and mortality from subsequent bleeding events Subarachnoid blood may be present in either case, although more commonly with aneurysm rupture Cavernous and venous hemangiomas are lower-flow lesions that produce less acute symptom onset Stroke may also occur from thrombosis or embolism of a normal vessel Cerebral infarction caused by occlusion of the anterior, middle, or posterior cerebral artery usually produces focal neurologic deficit rather than coma Acute occlusion of the carotid artery, however, may produce sufficient unilateral hemispheric swelling to cause herniation and coma Cerebral sinovenous thrombosis is most commonly seen with hypercoagulable states or as a sequela of infections of the ear or sinus Swelling or hemorrhage from infarcted brain can cause increased ICP, leading to decreased cerebral perfusion pressure and coma Focal symptoms vary based on the size and location of brain with inadequate blood supply Vascular accidents in the cerebellum present with combinations of ataxia, vertigo, nausea, occipital headache, and resistance to neck flexion Coma is an unusual early sign of infarction of cerebral structures but becomes more common as lower anatomic centers are affected Occlusion of the basilar artery may result in upper brainstem infarction, resulting in rapid onset of coma, as does hemorrhage or infarction of the pons Posterior reversible encephalopathy syndrome (PRES, a.k.a reversible posterior leukoencephalopathy syndrome [RPLS]) causing ALOC is associated with autoimmune disease, sepsis, nephrotic syndrome, or immunosuppressive agents Cerebrospinal Fluid Shunt Problems Children with congenital or acquired hydrocephalus as a result of prematurityrelated hemorrhage, neoplasm, or trauma depend on the continued function of an intraventricular shunt to drain CSF and maintain normal ICP (see Chapter 122 Neurosurgical Emergencies ) The most common shunt type is ventriculoperitoneal (VP), draining CSF from a lateral cerebral ventricle through a small skull burr hole and valve with an attached reservoir into the peritoneum via subcutaneous tubing running through neck, chest, and abdomen CSF shunts may malfunction for many reasons, including shunt infection, tubing blockage, rupture, disconnection, or valve malfunction The risk of failure is greatest during the first months after shunt placement or revision Systemic Abnormalities The second major category of disorders causing coma listed in Table 17.2 arise in organs other than the CNS and affect the brain diffusely These abnormalities alter neuronal activity by a variety of mechanisms, including decreasing metabolic substrates required for normal function (e.g., hypoxia, hypotension, hypoglycemia, other electrolyte abnormalities), altering the rate of intracellular chemical reactions (e.g., hypothermia, hyperthermia), and introducing extraneous toxins into the CNS Children with autoimmune disease such as systemic lupus erythematosus, Behỗet disease, multiple sclerosis, and acute disseminated encephalomyelitis (ADEM, a.k.a postinfectious encephalitis) may present with ALOC due to inflammation of brain parenchyma Hypoxia Oxygen delivery to the brain may be adversely affected by disorders that compromise a patient’s airway, breathing, or circulation Neurons are the cells most sensitive to oxygen deprivation, and they will cease to function within seconds after being deprived of adequate levels of oxygen Hypoxic coma may result from airway obstruction, pulmonary disease, severe acute anemia, severe methemoglobinemia, carbon monoxide poisoning, or asphyxia (e.g., drowning) Permanent CNS dysfunction results from total anoxia lasting more than to minutes at normal body temperatures; lesser degrees of hypoxia may be tolerated for longer periods Submersion in near-freezing water may cool the brain sufficiently to exert a neuroprotective effect, the magnitude of which is not usually apparent in the emergency department Hypercarbia may accompany hypoxia and may contribute to neurologic depression and coma Cardiovascular Abnormalities ALOC may be produced by poor cerebral perfusion resulting from insufficient cardiac output or hypotension, as in hemorrhage, dehydration, septic shock, dysrhythmia, and intoxication Hypertensive encephalopathy is distinguished by headache, nausea, vomiting, visual disturbance, ALOC, or coma in the presence of a blood pressure greater than the 95th percentile for age and gender (see Chapter 37 Hypertension ) The acute onset of severe hypertension may reflect ongoing renal (e.g., unilateral renal artery stenosis, acute glomerulonephritis), endocrine (e.g., pheochromocytoma), or cardiac (e.g., aortic coarctation) pathology, or it may be the result of a toxic ingestion (e.g., cocaine) Hypertension accompanied by bradycardia may be caused by increased ICP Disorders of Thermoregulation Hypothermia or hyperthermia in the pediatric patient is usually caused by prolonged environmental exposure to temperature extremes, such as those found in cold water or in a closed car in sunlight (see Chapter 90 Environmental Emergencies, Radiological Emergencies, Bites and Stings ) The child who becomes comatose as a result of abnormal core temperature will have multiple organ system abnormalities in addition to CNS dysfunction Mental impairment is progressive as body temperature is lowered, as each fall of 1°C produces a 6% decline in cerebral blood flow At 29° to 31°C, confusion or delirium is present, as is muscular rigidity Patients with core temperatures of 25° to 29°C are comatose with absent deep tendon reflexes and fixed, dilated pupils CNS findings in hyperthermia include headache, vomiting, and obtundation, leading to coma and/or seizures, especially above 41°C Nonenvironmental causes of hyperthermia include neuroleptic malignant syndrome, serotonin syndrome, and malignant hyperthermia Toxic Ingestions ... hemangiomas Rupture of an AVM is the most common cause of spontaneous intracranial bleeding among pediatric patients The hemorrhage is arterial in origin and located within the parenchyma, but it... sufficiently to exert a neuroprotective effect, the magnitude of which is not usually apparent in the emergency department Hypercarbia may accompany hypoxia and may contribute to neurologic depression... may be caused by increased ICP Disorders of Thermoregulation Hypothermia or hyperthermia in the pediatric patient is usually caused by prolonged environmental exposure to temperature extremes,