Needle tip visualization during ultrasound-guided vascular access: short-axis vs long-axis approach

Abstract

Objectives

Ultrasound guidance for central venous catheterization improves success rates and decreases complications when compared to the landmark technique. Prior research has demonstrated that arterial and/or posterior vein wall puncture still occurs despite real-time ultrasound guidance. The inability to maintain visualization of the needle tip may contribute to these complications. This study aims to identify whether long-axis or short-axis approaches to ultrasound-guided vascular access afford improved visibility of the needle tip.

Methods

A prospective trial was conducted at a level I trauma center with an emergency medicine residency. Medical students and residents placed needles into vascular access tissue phantoms using long-axis and short-axis approaches. Ultrasound images obtained at the time of vessel puncture were then reviewed. Primary outcome measures were visibility of the needle tip at the time of puncture and total time to successful puncture of the vessel.

Results

All subjects were able to successfully obtain simulated blood from the tissue phantom. Mean time to puncture was 14.8 seconds in the long-axis group and 12.4 seconds in the short-axis group (P = .48). Needle tip visibility at the time of vessel puncture was higher in the long-axis group (24/39, 62%) as opposed to the short-axis group (9/39, 23%) (P = .01).

Conclusions

In a simulated vascular access model, the long-axis approach to ultrasound-guided vascular access was associated with improved visibility of the needle tip during vessel puncture. This approach may help decrease complications associated with ultrasound-guided central venous catheterization and should be prospectively evaluated in future studies.

Introduction

Physicians use ultrasound to facilitate needle placement for a wide variety of procedures, including (but not limited to) central and peripheral venous catheterization, arterial catheterization, regional nerve blocks, paracentesis, thoracentesis, lumbar puncture, pericardiocentesis, and arthrocentesis. Multiple studies have demonstrated an improved success rate and a decreased complication rate for ultrasound-guided vascular access as compared to the traditional landmark technique [1], [2], [3]. Complications using ultrasound guidance for needle placement have been described [3], [4], and lack of visualization of the needle tip during needle advancement may contribute to inadvertent puncture of vital anatomic structures and failed vascular access attempts.

Needle placement with ultrasound guidance can be performed using either a short-axis (out-of-plane) or a long-axis (in-plane) approach to visualize the needle as it is advanced toward the desired target. In the short-axis approach, the transducer is oriented transversely to the vessel, and the vessel appears as a circular anechoic structure. When the needle is inserted perpendicular to the transducer, it bisects the plane of imaging and therefore appears as a hyperechoic “dot” on the ultrasound screen (Fig. 1). In the long-axis approach, a longitudinal view of the vein is obtained, and the vein appears as a tubular anechoic structure. The needle is inserted parallel to the transducer's longest axis directly under the center of the transducer and therefore lies completely within the plane of imaging (Fig. 2).

A comparison of short-axis and long-axis approaches to ultrasound-guided vascular access by novice physicians on a tissue phantom demonstrated a decreased time to puncture using the short-axis approach [5]. Two previous studies comparing needle visibility using short-axis and long-axis approaches (and multiple different needles of various size, with and without image-enhancing properties) demonstrated superior needle visibility using the long-axis approach, but these studies were performed by analyzing static images obtained after needles were previously placed by experienced operators [6], [7]. We hypothesize that the long-axis approach will afford improved visualization of the needle tip during simulated ultrasound-guided vascular access.