Cerebrospinal fluid shunts: an experimental comparison of flow rates and pressure values in various commercial systems

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Abstract
✓ The flow-rate characteristics of selected cerebrospinal fluid (CSF) shunt systems under a constant hydrostatic pressure differential were studied and compared with measurements of the opening pressure (OP) and closing pressure (CP). The usual technique of measuring the CP correlated poorly with actual flow rates. The OP measurement revealed variations from 5 to 600 mm H2O in the hydrostatic pressure actually needed to open the valve. The flow-rate values are important in that some shunt systems will not deliver distilled water at rates significantly in excess of 0.35 ml/min (the probable average normal CSF production rate) at hydrostatic pressure differentials of 150 mm H2O. However, this may not be apparent clinically since much higher hydrostatic pressure differentials are present in the erect patient with a CSF shunt where the ventricular pressure and shunt siphoning pressures are additive.