A Preclinical Study Examining the Role of Fluid Viscosity in Cerebrospinal Fluid Drainage Via an External Ventricular Drain

BACKGROUND: Measuring intracranial pressure with an external ventricular drain (EVD) if blood is present in the system may alter the rate at which cerebrospinal fluid drains. This study explored the differences in EVD drainage rate between 0.9% NaCl (saline) and blood. METHODS: This preclinical study used an acrylic chamber to represent the skull and EVD tubing. Four conditions were simulated by alternately filling the chamber, EVD tubing, or both, with saline or blood. The EVD was opened to drain at a pressure of 15 mm Hg with the column set for 10 mm Hg. The volume of drainage in the first minute after the drain opening determined the rate. RESULTS: There were significant differences in drainage rates among the 4 conditions ( P <0.0001). A Tukey post hoc test showed that when the system contained only saline, the drainage rate was significantly higher than that with blood in the tubing, the chamber, or both ( P <0.05). There was no significant difference in drainage rate with blood in the EVD tubing ( P =0.424). CONCLUSIONS: The physical properties of the cerebrospinal fluid drainage are key factors in determining drainage efficiency. The high viscosity of blood significantly inhibits drainage, and the low resistance properties of saline optimize drainage dynamics. These data provide an important direction for improving clinical EVD management.