Comparison between femoral vein diameter and inferior vena cava diameter by ultrasound in estimation of central venous pressure in mechanically ventilated patients

Abstract

Background Bedside ultrasonography is used as a noninvasive method for hemodynamic monitoring, evaluation of inferior vena cava (IVC) diameter by sonography provides an alternative tool for evaluation of intravascular volume. Femoral vein is a superficial compliant vessel, and images can be easily obtained. A significant correlation between central venous pressure (CVP) and common iliac vein pressure was reported previously, meaning that the femoral vein could be a noninvasive alternative to the CVP. Patients and methods We enrolled 100 adult patients in this study. During measurement, the patient was in supine position. The CVP was uniformly measured at the end of expiration, with the pressure transducer having been zeroed at the level of mid axillary line. IVC image was obtained using General Electric ultrasound machine and 3.5-MHz convex probe. The transducer is placed in a vertical plane in the subxiphoid view. The intrahepatic portion of the IVC was visualized as it entered the right atrium. Approximately 3–4 cm from the junction of the IVC and right atrium, the IVC diameter was obtained. Using M mode, the maximum and minimum diameter during inspiration and expiration diameter were recorded, respectively. To get the femoral vein diameter (FVD), we scanned the femoral triangle starting at the inguinal crease using a linear array transducer (5–10 MHz). FVD was measured just caudal to the saphenofemoral junction. Results We enrolled 100 patients in this study. Their mean age was 56 years, mean CVP was 6 cm H2O, mean IVC diameter during inspiration was 15 cm, whereas during expiration was 13.6 cm, and the FVD was 8.2 cm. There were significant correlations between both CVP and IVC diameter (insp and exp) and FVD. CVP correlation with FVD was 0.59, IVC diameter during inspiration with FVD was 0.41, and IVC diameter during expiration with FVD was 0.42. Conclusion FVD can be used as a noninvasive alternative method to assess intravascular volume status.