Geometric Changes of the Inferior Vena Cava in Trauma Patients Undergoing Volume Resuscitation: Insight into Dynamic Stresses Placed on Inferior Vena Cava Filters

Abstract

Dynamic changes in the anatomic geometry of the inferior vena cava (IVC) from changes in intravascular volume status may cause passive stresses on IVC filters. This study quantified the variability in IVC dimensions and anatomic orientation as influenced by intravascular volume changes to determine how it may affect complications of IVC filter placement including migration, tilting, and perforation. Retrospective computed tomography (CT) measurements of major and minor axis along with horizontal diameter of the IVC at 1 and 5 cm below the lowest renal veins (RVs) were assessed in 58 adult trauma patients in hypovolemic and postresuscitative states. IVC perimeter area and volumetric measurements were calculated and correlated with caval orientation. The mean volumes of the IVC segment were 9.34 mL on the initial CT scan and 11.52 mL on follow-up CT scans, with a mean increase of 51.5% (P < .01). At 1 and 5 cm below the RVs, the IVC expanded anisotropically, with the minor axis expanding by an average of 53.3% (P < .001) and 31.3% (P < .01), respectively, whereas the major axis only changed by 4.9% (P = .15) and 6.8% (P = .025). Surface area and perimeter at 1 cm below the lowest RV expanded by 67.5% (P < .001) and 11.2% (P < .01). At 5 cm below, the expansion of surface area and perimeter was 44.2% (P < .01) and 11.4% (P < .001). The IVC orientation was left anterior-oblique in all patients. Horizontal measurement significantly underestimated the IVC maximal diameter. With hypovolemia, at 1 and 5 cm below the lowest RV, the discrepancies between the horizontal and major axis diameters were 2.60 ± 1.27 mm (P < .001) and 2.13 ± 1.35 mm (P < .001), respectively, whereas the postresuscitation CT showed the same underestimation at 1 and 5 cm below the lowest RV, at 2.56 ± 1.25 mm (P < .01) and 2.38 ± 1.15 mm (P < .01), respectively. There is significant anisotropic variability of the infrarenal IVC geometry, with significantly greater expansive and compressive forces in the minor axis. There can be significant volumetric changes in the IVC with associated perimeter changes, but the left anterior-oblique caval configuration is always maintained. These significant dynamic forces are likely to affect IVC filter stability after implantation. The consistent obliquity may lead to underestimation of the IVC diameter used in anteroposterior venography and may influence initial filter selection.