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