Cerebrospinal Fluid

The first section of this chapter reviews cerebrospinal fluid (CSF) with respect to the anatomy of the CSF-containing spaces, physiology, and the effects of anesthetics and other influences. The second section reviews the relationship between CSF dynamics and intracranial pressure (ICP), anesthetics and drug-induced changes in CSF dynamics that increase or decrease ICP, and clinical situations wherein therapy to alter CSF dynamics may affect neurologic outcome.

Anatomy of cerebrospinal fluid spaces and properties of cerebrospinal fluid

The CSF is formed in the brain and circulates through macroscopic and extracellular fluid (ECF) spaces that are in continuity. The total volume of the macroscopic spaces ranges from 50 mL in infants to 140–150 mL in adults ( Table 3.1 ). Ventricular volume accounts for about 16% to 17% of macroscopic CSF volume in adults. Studies to determine the volumes of portions of the macroscopic CSF space using noninvasive imaging technology are ongoing. The ECF space surrounds the neuronal and glial elements of the central nervous system. Brain ECF volume is about 300 to 350 mL in adults exclusive of the macroscopic CSF space.

Table 3.1

Cerebrospinal Fluid Pressure and Volume in Humans

	Range ^∗
Cerebrospinal fluid (CSF) pressure (mmHg):
Children	3.0–7.5
Adults	4.5–13.5
CSF volume (mL):
Infants	40–60
Young children	60–100
Older children	80–120
Adults	100–160

∗ Values based on references 122–127.

Macroscopic Spaces

The choroid plexuses (CPs) of the lateral ventricles extend from the inferior horn to the central part of the ventricle. The CPs in the body of the lateral and third ventricles receive their blood supply from the posterior and anterior choroidal arteries, respectively. The CPs in the temporal horns and the fourth ventricle are supplied by the superior and posterior inferior cerebellar arteries, respectively. The nervous supply to the CPs includes branches of the vagus, glossopharyngeal, and sympathetic nerves.

Extracellular Fluid Spaces

The ECF spaces of the brain and spinal cord, unlike those of other organs in the body, are small in diameter (180 Å). Exchange between cerebral capillaries and the ECF is limited because the capillary membrane is highly impermeable. This blood–brain barrier (BBB) consists of two elements. First, the cells of the cerebral capillary endothelium are joined by tight junctions (zonula occludens) that restrict the intercellular movement of molecules having a diameter of 20 Å or more. Second, astrocyte foot processes surround the capillaries. Evidence shows that the ECF spaces communicate with lymphatic channels.

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