<P> The Monro--Kellie hypothesis is named after Edinburgh doctors Alexander Monro and George Kellie . </P> <P> One of the most damaging aspects of brain trauma and other conditions, directly correlated with poor outcome, is an elevated intracranial pressure . ICP is very likely to cause severe harm if it rises too high . Very high intracranial pressures are usually fatal if prolonged, but children can tolerate higher pressures for longer periods . An increase in pressure, most commonly due to head injury leading to intracranial hematoma or cerebral edema, can crush brain tissue, shift brain structures, contribute to hydrocephalus, cause brain herniation, and restrict blood supply to the brain . It is a cause of reflex bradycardia . </P> <P> In general, symptoms and signs that suggest a rise in ICP include headache, vomiting without nausea, ocular palsies, altered level of consciousness, back pain and papilledema . If papilledema is protracted, it may lead to visual disturbances, optic atrophy, and eventually blindness . The headache is classically a morning headache which may wake them from sleep . The brain is relatively poorly supplied by oxygen as a result of mild hypoventilation during the sleeping hours and also cerebral edema may worsen during the night due to the lying position . The headache is worse on coughing, sneezing or bending and progressively worsens over time . There may also be personality or behavioral changes . </P> <P> In addition to the above, if mass effect is present with resulting displacement of brain tissue, additional signs may include pupillary dilatation, abducens palsies, and the Cushing's triad . Cushing's triad involves an increased systolic blood pressure, a widened pulse pressure, bradycardia, and an abnormal respiratory pattern . In children, a low heart rate is especially suggestive of high ICP . </P>

What is the earliest sign of increased intracranial pressure
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