Murphy Erin H, Arko Frank R, Trimmer Clayton K, Phangureh Varinder S, Fogarty Thomas J, Zarins Christopher K
University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
J Vasc Surg. 2009 Oct;50(4):835-42; discussion 842-3. doi: 10.1016/j.jvs.2009.05.012. Epub 2009 Aug 6.
The geometry and dynamics of the vena cava are poorly understood and current knowledge is largely based on qualitative data. The purpose of this study is to quantitate the dimensional changes that occur in the infrarenal inferior vena cava (IVC), in response to changes in intravascular volume.
IVC dimensions were measured at 1 cm and 5 cm below the renal veins, on serial contrasted computed tomographic (CT) scans, in 30 severely injured trauma patients during hypovolemic (admission) and fluid resuscitated (follow-up) states. Changes in volume of the infrarenal segment were calculated and correlated with changes in IVC diameter and orientation. The orientation of the infrarenal caval segment was quantified as the angulation of the major axis from the horizontal. A representation of the IVC diameter, as would be seen on standard anterior-posterior venographic imaging, was determined by projecting the CT image of the major axis onto a coronal plane. CT representations of venographic diameters were compared with measurements of the true major axis to assess accuracy of venograms for caval sizing and filter selection.
All patients had evidence of a collapsed IVC (<15 mm minor axis dimension) on admission. Mean time between admission and follow-up CT was 49.5 (range: 1-202) days. The volume of the infrarenal segment increased more than twofold with resuscitation, increasing from 6.9 +/- 2.2 (range: 3.1-12.4) mL on admission, to 15.7 +/- 5.0 (range: 9.2-28.5) mL on follow-up (P < .01). At both 1 and 5 cm below the renal veins, the IVC expanded anisotropically such that the minor axis expanded up to five times its initial size accommodating 84% of the increased volume of the segment, while only small diameter changes were observed in the major axis accounting for less than 5% of the volume increase (P < .001). Further, the IVC was left-anterior-oblique in all patients, with the major axis 26 degrees off the horizontal on average. This orientation did not change significantly with volume resuscitation (P > 0.5). The obliquity of the IVC resulted in significant underestimation of caval size of up to 6.8 mm, when using the venographic representation for sizing instead of the true major axis (P < 0.001).
In response to changes in intravascular volume, the IVC undergoes profound anisotropic dimensional changes, with greater displacement seen in the minor axis. In addition, the IVC is oriented left-anterior oblique and caval orientation is not altered by changes in volume status. IVC obliquity may result in underestimation of caval size by anterior-posterior venogram.
下腔静脉的几何结构和动力学尚未得到充分了解，目前的认识主要基于定性数据。本研究的目的是量化肾下下腔静脉（IVC）在血管内容量变化时发生的尺寸变化。
在30例严重受伤的创伤患者处于低血容量状态（入院时）和液体复苏状态（随访时）时，通过连续的对比计算机断层扫描（CT），在肾静脉下方1 cm和5 cm处测量IVC尺寸。计算肾下段的体积变化，并将其与IVC直径和方向的变化相关联。肾下段的方向通过长轴与水平线的夹角来量化。通过将长轴的CT图像投影到冠状面上，确定在标准前后静脉造影成像上可见的IVC直径。将静脉造影直径的CT表现与真实长轴的测量值进行比较，以评估静脉造影在腔静脉大小测量和滤器选择方面的准确性。
所有患者入院时均有IVC塌陷的证据（短轴尺寸<15 mm）。入院CT与随访CT之间的平均时间为49.5天（范围：1 - 202天）。肾下段的体积在复苏后增加了两倍多，从入院时的6.9±2.2 mL（范围：3.1 - 12.4 mL）增加到随访时的15.7±5.0 mL（范围：9.2 - 28.5 mL）（P <.01）。在肾静脉下方1 cm和5 cm处，IVC均呈各向异性扩张，短轴扩张至初始大小的五倍，容纳了该段增加体积的84%，而长轴仅出现较小的直径变化，占体积增加的不到5%（P <.001）。此外，所有患者的IVC均为左前斜位，长轴平均与水平线成26度角。这种方向在容量复苏后没有显著变化（P > 0.5）。当使用静脉造影表现来测量腔静脉大小而不是真实长轴时，IVC的倾斜导致腔静脉大小被显著低估，低估幅度高达6.8 mm（P < 0.001）。
随着血管内容量的变化，IVC会发生显著的各向异性尺寸变化，短轴的位移更大。此外，IVC呈左前斜位，腔静脉方向不会因容量状态的变化而改变。IVC的倾斜可能导致前后位静脉造影低估腔静脉大小。
