Manejo en hipertension intracraneal

Crit Care Clin 22 (2007) 713–732

Management of Intracranial Hypertension
Leonardo Rangel-Castillo, MDa, Claudia S. Robertson, MDb,*
a

Research Assistant, Department of Neurosurgery, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA b Professor, Department of Neurosurgery, Baylor College of Medicine, Houston, Texas 77030, USA

Intracranial hypertension is a commonneurologic complication in critically ill patients. Intracranial hypertension is the common pathway in the presentation of many neurologic and non-neurologic disorders. The underlying pathophysiology of increased intracranial pressure (ICP) is the subject of intense basic and clinical research, which has led to advances in understanding of the physiology related to ICP. Few specific treatment optionsfor intracranial hypertension have been subjected to randomized trials, however, and most management recommendations are based on clinical experience. Intracranial pressure Normal values In normal individuals with closed cranial fontanelles, central nervous system contents, including brain, spinal cord, blood, and cerebrospinal fluid (CSF), are encased in a noncompliant skull and vertebral canal,constituting a nearly incompressible system. There is a small amount of capacitance in the system provided by the intervertebral spaces. In the average adult, the skull encloses a total volume of 1450 mL: 1300 mL of brain, 65 mL of CSF, and 110 mL of blood [1]. The Monroe-Kellie hypothesis states the sum of the intracranial volumes of blood, brain, CSF, and other components is constant, and thatan increase in any one of these must be offset by an equal decrease in another, or else pressure increases. An increase in
This article was supported by NIH grant P01-NS38660. * Corresponding author. E-mail address: claudiar@bcm.tmc.edu (C.S. Robertson). 0749-0704/07/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.ccc.2006.06.003 criticalcare.theclinics.com

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pressure caused by an expanding intracranial volume is distributed evenly throughout the intracranial cavity [2,3]. The normal range for ICP varies with age. Values for pediatric subjects are not as well established. Normal values are less than 10 to 15 mm Hg for adults and older children, 3 to 7 mm Hg for young children, and 1.5 to 6 mm Hg for term infants. ICPcan be subatmospheric in newborns [4]. For the purpose of this article, normal adult ICP is defined as 5 to 15 mm Hg (7.5–20 cm H2O). ICP values of 20 to 30 mm Hg represent mild intracranial hypertension; however, when a temporal mass lesion is present, herniation can occur with ICP values less than 20 mm Hg [5]. ICP values greater than 20 to 25 mm Hg require treatment in most circumstances.Sustained ICP values of greater than 40 mm Hg indicate severe, life-threatening intracranial hypertension. Cerebral dynamics overview Cerebral perfusion pressure (CPP) depends on mean systemic arterial pressure (MAP) and ICP by the following relationship: CPP ¼ MAP À ICP where MAP ¼ ð1=3 systolic BPÞ þ ð2=3 diastolic BPÞ As a result, CPP can be reduced from an increase in ICP, a decrease in bloodpressure, or a combination of both factors. Through the normal regulatory process called pressure autoregulation, the brain is able to maintain a normal cerebral blood flow (CBF) with a CPP ranging from 50 to 150 mm Hg. At CPP values less than 50 mm Hg, the brain may not be able to compensate adequately, and CBF falls passively with CPP. After injury, the ability of the brain to pressure autoregulatemay be absent or impaired, and even with a normal CPP, CBF can passively follow changes in CPP. When CPP is within the normal autoregulatory range (50–150 mm Hg), this ability of the brain to pressure autoregulate also affects the response of ICP to a change in CPP [6–8]. When pressure autoregulation is intact, decreasing CPP results in vasodilation of cerebral vessels, which allows CBF to remain...