Ultrasonographic Investigation of the Effect of Inguinal Compression on the Cross-sectional Area of the Femoral Vein

Abstract

Objectives:  The reverse Trendelenburg position increases the cross-sectional area (CSA) of the femoral vein, making it easier to cannulate, although this position is potentially harmful in hypovolemic patients. The authors hypothesized that compression above the femoral vein increases the CSA of the femoral vein during emergency cannulation.

Methods:  Ultrasound was used to measure the CSA of the femoral vein of 20 healthy volunteers. The following five measurements were made inferior to the inguinal crease: 1) in the horizontal supine position (control), 2) with inguinal compression 2 cm above the inguinal crease (at the point of arterial pulsation and its medial side), 3) in the Trendelenburg position 15°, 4) in the Trendelenburg position 15° plus inguinal compression, and 5) in the reverse Trendelenburg position 15°.

Results:  Femoral vein CSA was increased by 35% by inguinal compression in the horizontal supine position (p < 0.001) and was decreased by the Trendelenburg position (p < 0.001). However, inguinal compression increased the CSA by 66% in the Trendelenburg position (p < 0.001). The reverse Trendelenburg position also increased the CSA of the femoral vein by 50% (p < 0.001).

Conclusions:  Inguinal compression presents an alternative method for increasing the CSA of the femoral vein for venous catheterization in normal patients.

In the critically ill patient with hemodynamic instability, central venous catheterization is often necessary. Although the internal jugular or the subclavian veins are commonly chosen, the femoral vein is occasionally used, especially in emergency situations. However, this site carries a greater incidence of complications such as arterial puncture and hematoma.¹ Theoretically, successful cannulation is most likely when the vein is maximally distended. The cross-sectional area (CSA) of the femoral vein increases significantly in the reverse Trendelenburg position, with the Valsalva maneuver, or with humming. ^2–5 However, these maneuvers can decrease venous return to the heart and cause hypotension, and are thus often unsuitable. The aim of this study was to evaluate the use of compression applied just above the inguinal crease to increase the CSA of the femoral vein in normal volunteers.

Methods

Study Design

This was an observational study using normal volunteer human subjects. It was approved by the institutional review board, and written informed consent was obtained from each volunteer.

Study Setting and Population

Twenty healthy male subjects were enrolled. Subjects taking any medication, with a history of prior central venous catheterization, and with prior groin surgery were excluded.

Study Protocol

Subjects were placed on an operating room table in the horizontal supine position, and ultrasound images were obtained from the right common femoral vein using a two-dimensional 7.5-MHz linear probe aligned transversely 0–2 cm inferior to the inguinal crease. The same investigator (JTK) obtained all images to achieve consistency in measurements. The probe was held perpendicular to the skin and applied with the lightest possible pressure. The five measurements of the femoral vein were made with the probe held in the same position: 1) the horizontal supine position (control); 2) with inguinal compression (the inguinal compression was performed by compressing 2 cm above the inguinal crease as firmly and as broadly as possible with three fingers, just medial to the point of arterial pulsation); 3) in the Trendelenburg position 15°; 4) the Trendelenburg position 15° plus inguinal compression; and 5) in the reverse Trendelenburg position 15°. Measurements were made after at least 1 minute in each position.

Measurements

To exclude the effects of respiratory fluctuations, only images with maximal CSA of the femoral vein were selected. The CSA was calculated by preloaded software on the ultrasound machine (Vivid I ultrasound machine, GEMSI ultrasound, Tirat Carmel, Israel) after the investigator delineated the circumference of the femoral vein using an electronic marker.

Data Analysis

A 20% change in CSA was considered clinically relevant. The data were analyzed using the paired t-test or Wilcoxon’s signed rank test. Each p-value for the test was adjusted using a Bonferroni correction at an overall significant level < 0.05.

Results

Twenty men (age 27.6 ± 2.1 yr; height 174.9 ± 4.1 cm; weight 73.1 ± 6.3 kg) participated in the study. They were all within 15% of the ideal body weight. The mean CSAs (cm²) ± SD of the femoral vein in each position were as follows: 1.00 ± 0.28 (95% confidence interval [CI] = 0.87 to 1.14) in the horizontal supine position, 1.30 ± 0.30 (95% CI = 1.15 to 1.45) during inguinal compression, 0.70 ± 0.30 (95% CI = 0.55 to 0.85) in Trendelenburg position, 1.07 ± 0.40 (95% CI = 0.87 to 1.27) in Trendelenburg position plus inguinal compression, and 1.46 ± 0.34 (95% CI = 1.28 to 1.63) in the reverse Trendelenburg position.

Inguinal compression increased femoral vein CSA by 35 ± 33% (95% CI = 18% to 51%) in the horizontal position (p < 0.001). CSA was significantly reduced by 32 ± 16% (95% CI = 24% to 40%) in the Trendelenburg position, but inguinal compression then increased it by 66 ± 57% (95% CI = 38% to 94%; p < 0.001). The reverse Trendelenburg position also increased the CSA of the femoral vein by 50 ± 36% (95% CI = 33% to 68%; p < 0.001). There was no significant difference in CSA between compression in the horizontal supine position and the reverse Trendelenburg position.

Discussion

This study demonstrates that in healthy male volunteers, compression above the inguinal crease increases the CSA of femoral vein, both in the horizontal and in the Trendelenburg positions. When central venous access is required for resuscitation, the femoral vein is a highly accessible site. However, measures to increase its CSA, such as the reverse Trendelenburg position or the Valsalva maneuver, are often not preferred due to the reduction of venous return to the heart and possible worsening of hemodynamics. In contrast, Trendelenburg positioning for the purpose of increasing venous return can collapse the femoral vein, making cannulation more difficult. In this context, the inguinal compression can be useful because it increases the CSA without gravitational position change or influence on intrathoracic pressure.

We showed a decrease in the CSA of the femoral vein by placing subjects in the Trendelenburg position. In this position, inguinal compression was effective in increasing the CSA of the femoral vein. Although inguinal compression increases the CSA of the femoral vein in the supine or Trendelenburg position in healthy volunteers, the true effect of the inguinal compression on the patient who requires central venous access in clinical practices is unknown.

Although the inguinal compression increases the CSA of the femoral vein in supine or Trendelenburg position in healthy volunteers, the real effect of the inguinal compression on the patient who requires the central venous catheter in the emergency department remains to be studied. Furthermore, it also is uncertain if the success rate of the femoral cannulation could be increased by the inguinal compression.

Limitations

Lack of blinding of the investigator to the investigational maneuver, lack of standardization of inguinal compression, and the use of healthy volunteers were limitations of this study. Additionally, all subjects were within 15% of ideal body weight. Thus, in an obese subject, inguinal compression may be less effective. In addition, the fact that only one sonographer performed the imaging studies limits the generalizability of the findings.

Conclusions

Inguinal compression increases the CSA of the femoral vein in normal volunteers and thus may be a practical noninvasive method for increasing the CSA of the femoral vein during central venous cannulation.