Hypertonic saline lowers ICP by dehydrating brain tissue without affecting cerebral blood volume

Object. The pathogenesis of traumatic brain swelling remains unclear. The generally held view is that brain swelling is caused primarily by vascular engorgement and that edema plays a relatively minor role in the swelling process. The goal of this study was to examine the roles of cerebral blood volume (CBV) and edema in traumatic brain swelling.Methods. Both brain-tissue water and CBV were measured in 76 head-injured patients, and the relative contribution of edema and blood to total brain swelling was determined. Comparable measures of brain-tissue water were obtained in 30 healthy volunteers and CBV in seven volunteers. Brain edema was measured using magnetic resonance imaging, implementing a new technique for accurate measurement of total tissue water. Measurements of CBV in a subgroup of 31 head-injured patients were based on consecutive measures of cerebral blood flow (CBF) obtained using stable xenon and calculation of mean transit time by dynamic computerized tomography scanning after a rapid bolus injection of iodinated contrast material. The mean (± standard deviation) percentage of swelling due to water was 9.37 ± 8.7%, whereas that due to blood was −0.8 ± 1.32%.Conclusions. The results of this study showed that brain edema is the major fluid component contributing to traumatic brain swelling. Moreover, CBV is reduced in proportion to CBF reduction following severe brain injury.

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Reduction of Cerebrospinal Fluid Pressure by Hypocapnia: Changes in Cerebral Blood Volume, Cerebrospinal Fluid Volume, and Brain Tissue Water and Electrolytes

Journal of Cerebral Blood Flow & Metabolism ◽

10.1038/jcbfm.1987.90 ◽

1987 ◽

Vol 7 (4) ◽

pp. 471-479 ◽

Cited By ~ 29

Author(s):

Alan A. Artru

Keyword(s):

Cerebrospinal Fluid ◽

Brain Tissue ◽

Blood Volume ◽

Cerebral Blood Volume ◽

Tissue Water ◽

Group Iii ◽

Csf Pressure ◽

Intracranial Mass ◽

Group I ◽

Group Ii

The study examined the role of cerebral blood volume (CBV), cerebrospinal fluid (CSF) volume, and brain tissue water and electrolytes on CSF pressure during 4 h of hypocapnia in dogs, Group I (n = 6) was examined during hypocapnia (PaCO2 20 mm Hg), with no intracranial mass being present Group II (n = 6) was examined with an intracranial mass present (epidural balloon, CSF pressure 35 cm H2O), but no hypocapnia. In group III (n = 6), an intracranial mass was present, and hypocapnia was used to lower CSF pressure. In group I, hypocapnia initially reduced CBV from 3.4 to 2.4 ml. With continued hypocapnia, CBV reexpanded to 3.4 ml by 4 h. CSF volume changed reciprocally, so that intracranial CSF pressure remained constant. In group II, CBV remained steady (2.7 ml), and CSF volume fell only slightly, so that CSF pressure remained elevated. In group III, hypocapnia initially reduced CBV from 2.8 to 2.2 ml, and CSF pressure fell from 35 to 19 cm H2O. With continued hypocapnia, CBV rose to 2.8 ml by 4 h, but CSF volume fell from 6.1 to 5.0 ml, so that CSF pressure remained low. Net intracranial absorption of CSF did not exceed net intracranial CSF production, suggesting that CSF volume fell because hypocapnia improved access of intracranial CSF to spinal sites of CSF reabsorption. Brain tissue composition was not different among groups. The indicate that hypocapnia lowers elevated CSF pressure initially by lowering CBV. This CSF pressure-lowering effect is sustained (despite reexpansion of CBV) by a further reduction of CSF volume. In this model, brain tissue water or electrolytes did not contribute to changes in CSF pressure.

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