Fluid perfusion as a method of cerebrospinal fluid formation rate--critical appraisal.

The aim of the study was to evaluate whether or not cerebrospinal fluid formation rate (Vf) calculated according to the equation of Heisey et al., truly show the produced cerebrospinal fluid. For this reason Vf was simulated (40.6 microL/min) by an infusion pump in a plastic cylinder and the evaluation was done by comparing the results obtained between the calculated Vf and the simulated one. In both cases the result should be the same (40.6 micro/min). Other types of experiments were carried out by ventriculocisternal perfusion (92.4 microL/min) on anaesthetized and sacrificed cats. If the equation is correct, the calculated Vf for sacrificed animals should be zero, because there is no Vf in dead animals. The fact that the calculated Vf (46.5 microL/min) in the plastic cylinder was different (p < 0.0001) from the simulated one (40.6 microL/min) and that Vf was calculated even for dead animals (3-5 microL/min) clearly shows the that perfusion method may not be an accurate method for determination of Vf.