Impact of Air Bubbles on Cerebrospinal Fluid Drainage in Ventriculoperitoneal Shunts: An Experimental Validation

BACKGROUND AND OBJECTIVES: Airlock has been documented as a failure mechanism in various types of medical catheters, but it remains poorly characterized in ventriculoperitoneal (VP) shunts. The objective of this study was to determine whether catheter airlocks have the capability to induce VP shunt malfunction by impeding cerebrospinal fluid flow and to identify the conditions under which it might occur. METHODS: A laboratory experiment was conducted to investigate various induced air bubble occlusion scenarios in VP shunts. Variables tested included size and number of air bubbles within the catheter, the catheter internal diameter, and the presence of a BioGlide® coating. To assess air bubbles' impact on system function, shunts were connected to a water column to incrementally increase static pressure, and the minimum pressure needed to initiate flow was recorded. RESULTS: Many variables were found to be involved in VP shunt airlock obstruction in a laboratory setting, including number of air bubbles within catheters, catheter internal diameter, catheter coating, and intraperitoneal. Yet, air bubble length had minimal impact. As a result, in a complete VP shunt system (translucent ventricular catheter, medium-pressure valve, and BioGlide®-coated peritoneal catheter), the obstruction was such that, assuming and/or experimentally simulating an intraperitoneal pressure of 5 mm Hg, the presence of 7 air bubbles required a static pressure exceeding a normal intracranial pressure of 15 mm Hg before water flow initiated. A smaller internal catheter diameter increased the required static pressure to overcome airlock, whereas the BioGlide®-coated catheters reduced it. CONCLUSION: Air bubbles entrapped in VP shunts have the capability of obstructing CSF flow, more so as bubble number increases. Careful purging of the shunt system at implantation surgery may help prevent airlock issues.