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It is often difficult to measure cerebrospinal fluid(CSF)pressure in children.CSF flow through a spinal needle described by the equation:Flow= pressure/(needle constant x relative viscosity).Thus,CSF flow rate during lumbar puncture can be used to estimate CSF pressure.Because the viscosity of CSF is approximately the same as that of normal saline,0.9%NaCl was used to model CSF flow in the vitro.Flow of saline through various spinal needles was measured as pressure and and temperature were varied to determine needle constants and variation in viscosity with temperature. Counting periods for which the number of drops counted equals the pressure (in centimeters of H20)then were determined for each needle size.At patient temperatures less than 40 degrees C,counting periods were calculated at 21,29,and 12 seconds.Finally,the method was tested prospectively in 12 patients by comparing drop count(over the calculated counting period)to manometric pressure measurement.Drop counts were within 15%of manometric pressure in all patients.This method allows simple and rapid estimation of CSF pressure during lumbar puncture. |
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