Which caval diameter? Clarification manufacturer's instructions for inferior vena cava filter use and implications for practice

Abstract

To clarify manufacturer's instructions for inferior vena cava (IVC) filter use and implications for practice. Three vendors of IVC filters were contacted for clarification, with all stating that caval diameter limits are to be true maximum and true minimum cross-sectional diameters. To determine the implications of this, measurements were performed on 302 abdominal computed tomography studies in four transaxial dimensions perpendicular to the long axis including true maximum and minimum diameters, and measurements reflecting those typically taken on fluoroscopic cavography. Based on the true maximum and true minimum caval diameter limits as clarified by vendors, 22% of patients who would typically be considered suitable for IVC filter insertion based on frontal and lateral fluoroscopic cavography would be contraindicated, and 40% of patients who would typically be considered suitable for IVC filter insertion based on only frontal fluoroscopic cavography (as lateral projection is often not performed) would be contraindicated. There is a marked discordance between the vendor-clarified caval diameter limits of three common IVC filter devices and real-world caval geometry. Given the rarity of complications, this suggests a pressing need for revision of manufacturers' instructions for use statements to better reflect current safe routine clinical use, particularly from a medicolegal perspective.