The acute cerebral effects of changes in plasma osmolality and oncotic pressure

Mark Zornow, M. M. Todd, S. S. Moore

Research output: Contribution to journalArticle

90 Citations (Scopus)

Abstract

Although it is generally accepted that a decrease in plasma oncotic pressure may result in the formation of peripheral edema, the effect of a hypo-oncotic state on brain water content is less well known. Therefore, utilizing the technique of hollow-fiber plasma-pheresis to manipulate plasma composition, the authors examined the effects of acute changes in either plasma osmolality or colloid oncotic pressure on the EEG, regional cerebral blood flow, intracranial pressrue, and brain tissue specific gravity (as a measure of cerebral water content) in anesthetized, neurologically normal New Zealand white rabbits. Animals in which either osmolality or oncotic pressure was decreased by plasma replacement with an appropriate solution were compared with a group of control animals in which both of these variables were maintained constant. Animals in which plasma osmolality was decreased by 13 ± 6 mOsm/kg (from a baseline value of 295 ± 5 mOsm/kg) showed evidence of a significant increase in cortical water content (~ 0.5%), whereas a 65% reduction in oncotic pressure (from 20 ± 2 mmHg to 7 ± 1 mmHg) failed to produce any change. There were no significant differences in mean arterial pressure, central venous pressure, regional cerebral blood flow, or the EEG between any of the groups. Although intracranial pressure increased in all groups, the largest increase (8.1 ± 4.4 mmHg) occurred in those animals whose osmolality was reduced. The increase in intracranial pressure in animals rendered hypo-oncotic was no different form the 'control' group (2.4 ± 0.9 mmHg vs. 3.0 ± 1.5 mmHg). This study suggests that an acute fall in oncotic pressrue does not promote an increase on cerebral water content in the non-injured brain. Unlike peripheral tissues, the presence of the blood-brian barrier with its small pore size and limited permeability may serve to enhance the importance of osmolality and minimize the role of oncotic pressure in determining water movement between the vasculature and brain tissue.

Original languageEnglish (US)
Pages (from-to)936-941
Number of pages6
JournalAnesthesiology
Volume67
Issue number6
StatePublished - 1987
Externally publishedYes

Fingerprint

Osmolar Concentration
Pressure
Cerebrovascular Circulation
Water
Regional Blood Flow
Brain
Electroencephalography
Water Movements
Control Groups
Blood Component Removal
Specific Gravity
Central Venous Pressure
Intracranial Hypertension
Intracranial Pressure
Colloids
Permeability
Edema
Arterial Pressure
Rabbits

ASJC Scopus subject areas

  • Anesthesiology and Pain Medicine

Cite this

The acute cerebral effects of changes in plasma osmolality and oncotic pressure. / Zornow, Mark; Todd, M. M.; Moore, S. S.

In: Anesthesiology, Vol. 67, No. 6, 1987, p. 936-941.

Research output: Contribution to journalArticle

Zornow, Mark ; Todd, M. M. ; Moore, S. S. / The acute cerebral effects of changes in plasma osmolality and oncotic pressure. In: Anesthesiology. 1987 ; Vol. 67, No. 6. pp. 936-941.
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