Constant ventricular drainage: pitfalls and variables. Technical note.

After observing the erratic performance of a commercially available ventricular drainage system, we examined the hydrostatic pressure exerted by the system as a function of the volume of fluid within the drainage bag (at a constant height). Initially, 3 to 4 cm more than the expected 27 cm of height was required to achieve a drainage pressure of 20 mm Hg. As the volume of fluid increased, there was an initial precipitous fall from the 20 mm Hg preset pressure to 14 to 16 mm Hg; this pressure differential increased as the volume of drained fluid increased. Removal of air from the drainage bag resulted in an additional decrement in the observed hydrostatic pressure. These decrements in pressure were not apparent with another commercially available bag used commonly for ventricular drainage. We therefore recommend that, if ventricular drainage is to be accomplished against a constant hydrostatic pressure head, the system should be configured so that the actual hydrostatic pressure against which drainage occurs can be measured quickly and easily. The system should be checked at frequent intervals as the ventricular drainage bag fills. We note additional pitfalls in use of constant ventricular drainage and suggest solutions.