Hipertensión Intracraneal

MD Consult: Kliegman: Nelson Textbook of Pediatrics

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Kliegman: Nelson Textbook of Pediatrics, 19th ed.
Copyright © 2011 Saunders, An Imprint of Elsevier

Chapter 63 – Neurologic Emergencies and Stabilization
Patrick M. Kochanek,Michael J. Bell The care of critically ill children has advanced greatly over the past decades, and mortality rates have fallen. A remaining challenge is optimizing recovery after critical neurologic insults.

Neurocritical Care Principles
The brain has high metabolic demands, which are further increased during growth and development. Preservation of nutrient supply to the brain is the mainstayof care for children with evolving brain injuries. Intracranial dynamics describes the physics of the interactions of the contents—brain parenchyma, blood (arterial, venous, capillary) and cerebrospinal fluid (CSF)—within the cranium. Normally, brain parenchyma accounts for up to 85% of the contents of the cranial vault, and the remaining portion is divided between CSF and blood. The brain residesin a relatively rigid cranial vault, and cranial compliance decreases with age as the skull ossification centers gradually replace cartilage with bone. The intracranial pressure (ICP) is derived from the volume of its components and the bony compliance. The perfusion pressure of the brain (cerebral perfusion pressure [CPP]) is equal to the pressure of blood entering the cranium (mean arterialpressure [MAP]) minus the ICP, in most cases. Increases in intracranial volume can result from swelling, masses, or increases in blood and CSF volumes. As these volumes increase, compensatory mechanisms decrease ICP by (1) decreasing CSF volume (CSF is displaced into the spinal canal or absorbed by arachnoid villi), (2) decreasing cerebral blood volume (venous blood return to the thorax is augmented),and/or (3) increasing cranial volume (sutures pathologically expand or bone is remodeled). Once compensatory mechanisms are exhausted (the increase in cranial volume is too large), small increases in volume lead to large increases in ICP or intracranial hypertension (Fig. 63-1). As ICP continues to increase, brain ischemia can occur as CPP falls. Further increases in ICP can ultimately displacethe brain downward into the foramen magnum—a process called cerebral herniation, which can become irreversible in minutes and may lead to severe disability or death. Oxygen and glucose are required by brain cells for normal functioning, and these nutrients must be constantly supplied by cerebral blood flow (CBF). Normally, CBF is constant over a wide range of blood pressures (blood pressureautoregulation of CBF) via actions mainly within the cerebral arterioles. Cerebral arterioles are maximally dilated at lower blood pressures and maximally constricted at higher pressures so that CBF does not vary during normal fluctuations (Fig. 63-2). Acid-base balance of the CSF (often reflected by acute changes in PaCO2), body/brain temperature, glucose utilization, and other vasoactive mediators(i.e., adenosine, nitric oxide) can also affect the cerebral vasculature.

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MD Consult: Kliegman: Nelson Textbook of Pediatrics

http://www.mdconsult.com/books/page.do?eid=4-u1.0-B978-1-4377-075...

Knowledge of these concepts is instrumental to preventing secondary brain injury. Increases in CSF pH that occur because of inadvertent hyperventilation (decreasedPaCO2) can produce cerebral ischemia. Hyperthermia-mediated increases in cerebral metabolic demands may damage vulnerable brain regions after injury. Hypoglycemia can produce neuronal death when CBF fails to compensate. Prolonged seizures can lead to permanent injuries if hypoxemia occurs from loss of airway control. Attention to detail and constant reassessment are paramount in managing children...