Effect of head and shoulder positioning on the cross-sectional area of the subclavian vein in obese subjects

Abstract

Objective

Head and shoulder positioning may affect cross-sectional area (CSA) and location of the subclavian vein (SCV). We investigated the CSA of the SCV and the depth of the SCV, depending on the head and shoulder positions.

Methods

In 24 healthy obese volunteers, the short axis ultrasound images of the SCV and adjacent structures were obtained in three different head positions (neutral, 30° turned to the contralateral side, and 30° turned to the ipsilateral side) and two different shoulder positions (neutral and lowered). Images of the right and left SCVs were obtained in the supine and Trendelenburg positions. Subsequently, the CSA and depth of the SCV were measured.

Results

Significant differences were found in the CSA of the SCV in different head positions (30° turned to contralateral side vs. neutral: −0.06 cm², 95% confidence interval [CI], −0.10 to −0.02; P_corrected = 0.002, 30° turned to contralateral side vs. 30° turned to ipsilateral side: −0.16 cm², 95% CI, −0.22 to −0.11; P_corrected < 0.001, Neutral vs. 30° turned to ipsilateral side: −0.10 cm², 95% CI, −0.14 to −0.07; P_corrected < 0.001). The CSA of the SCV was significantly different, depending on shoulder positions (neutral vs. lowered: 0.44 cm², 95% CI, 0.33 to 0.54; P_corrected < 0.001), and body position (supine vs. Trendelenburg: −0.15 cm², 95% CI, −0.19 to −0.12; P_corrected < 0.001). However, the depth of the SCV did not differ with respect to head, shoulder, and body positions.

Conclusions

Ipsilateral 30° head rotation, neutral shoulder position, and Trendelenburg position significantly enhanced the CSA of the SCV in obese participants.

Introduction

Central venous catheterization permits the measurement of hemodynamic variables and allows delivery of medications and nutritional support that cannot be administered safely through peripheral venous catheters [1]. The subclavian vein (SCV) is a favored access site for central venous catheterization because of the lower risk of catheter-related infections and thrombosis, and less collapsibility [2,3]. However, SCV catheterization is more difficult than other venous sites, including the internal jugular vein or femoral vein. Furthermore, serious complications such as pneumothorax, hematoma, or hemothorax can occur during SCV catheterization [1,4,5].

A previous study showed that success at the first pass was significantly correlated with the diameter of the internal jugular vein during catheterization of the internal jugular vein [6]. Therefore, an increased cross-sectional area (CSA) of the SCV may help increase the chance of successful puncture of the SCV. Several strategies have been suggested to increase the CSA of the SCV, including the Trendelenburg position [7,8], or positive intrathoracic pressure [7]. Currently, bedside ultrasonography is widely used for central venous catheterization as it improves the success rate of SCV catheterization and reduces catheterization-related complications [9]. However, ultrasound is not available in all clinical situations. Even with the ultrasound-guided approach, a higher body mass index limits the ability to visualize the SCV [10]. Therefore, an increased CSA may facilitate successful SCV puncture during blind and ultrasound-guided approaches of SCV catheterization.

SCV catheterization is more difficult in obese patients owing to indistinct landmarks and increased depth between the skin and SCV. The introducer needle may be relatively short to approach the SCV, and the entry angle of the needle tip may be increased, thereby increasing the risk of pneumothorax. The Trendelenburg position, a strategy for enhancing the CSA of the SCV, has been reported to increase the peak inspiratory and driving pressure, and reduce lung compliance in obese patients [11,12], which may interfere with oxygenation [12]. The effect of head and shoulder positions on the CSA of SCV has not been investigated yet in obese subjects. In the present study, we evaluated the effect of different head and shoulder positions on the CSA of the SCV in obese participants.