Introduction

Emergency physician expertise in the use of ultrasound for obtaining vascular access is widespread because of its clinical benefit. Patients may not have accessible superficial veins. Obesity and decreased intravascular volume further increase the challenges. Central venous access has known complications that include pneumothorax and injury to great vessels. Bedside ultrasound may decrease the complication rate by allowing direct, real-time visualization of vascular targets, decreasing the need for multiple attempts, and avoiding arterial injury.^1,² The application of ultrasound for invasive and therapeutic procedures has become standard as reflected in the 2006 policy statement of the American College of Emergency Physicians on emergency ultrasound.³ Over the past decade, wide acceptance of the benefits of ultrasound-guided vascular access has led to the recommendation that ultrasound guidance be used routinely in obtaining central vascular access.^4,⁵ Debate regarding the role of ultrasound has shifted to a focus on implementation of these recommendations and their cost-effectiveness.⁶^–⁹ Research is now largely focused on improving education and training techniques or documenting the adoption of ultrasound to augment central venous access in a wider variety of settings.^10,¹¹

How to Scan and Scanning Protocols

Ultrasound-guided central venous access is accomplished with many of the same techniques as used by the traditional landmark approach. Patient positioning, informed consent, use of sterile technique with full draping, and selection of the anatomic site should be undertaken in the usual manner.

Either a two- or single-operator technique is acceptable.¹² A single operator will use the dominant hand to advance and aspirate the needle while manipulating the transducer with the opposite hand. In a two-operator procedure, the cannulating operator will concentrate on the needle and syringe, and the probe will be held steady by the second operator.

Two techniques are commonly accepted for achieving ultrasound-guided vascular access. In the static technique, ultrasound is used to identify vascular structures in relation to external landmarks, and then the ultrasound device is set aside and cannulation performed in the usual manner. The dynamic technique involves real-time, direct visualization of entry of the needle into the vein by ultrasound and seems to be preferable, particularly when the venous structures are small.¹³ In this case, once the vein has been accessed (or a “flash” of blood is seen), the ultrasound device is set aside.

The probe most conducive to central venous access is a linear-array high-frequency (5- to 12-MHz) probe (Fig. 6.1). Care should be taken to identify the side of the probe bearing the indicator mark that corresponds to the on-screen indicator. This will allow the most intuitive positioning of the probe during venous access such that medial on the patient is medial on the screen of the machine as viewed by the operator when attempting cannulation (Fig. 6.2).

Fig. 6.1 Image of a high-frequency, or linear, transducer.

Fig. 6.2 Position of the transducer to obtain a transverse image of the internal jugular vein.

Note that as the operator is standing at the patient’s head, the indicator is pointing toward the patient’s left. This ensures that when the operator is looking at the screen, the patient’s left and the operator’s left are the same. This minimizes confusion if the needle track needs to be adjusted.

Once a site has been chosen, usually the internal jugular or femoral, it should be evaluated with ultrasound to identify the artery and the vein (Fig. 6.3). When compared with their accompanying veins, arteries appear thick walled, more circular, and pulsatile on ultrasound. Arteries do not compress with light pressure. Veins are more irregular in shape, sometimes appearing triangular rather than round, and compress with light pressure (see Videos 1 and 2). Use of color Doppler can also aid in identification (see Video 3).

Fig. 6.3 Transverse anatomy of the vessels of the neck.

In this image, the internal jugular (IJ) is seen lying on top of the carotid artery. The IJ is large and oval in shape. Direct pressure over it should cause slight collapse. The carotid remains stable in size, appearance, and compressibility. It is usually small, round, and noncompressible. Overlying the vessels is the sternocleidomastoid muscle.

Videos 1, 2, and 3 can be found on Expert Consult @ www.expertconsult.com.

It is often easiest to begin with the probe in a transverse orientation. In this view, the vessels appear in cross section as round or oval structures (see Fig. 6.3). The depth of the target vessel and its relationship to surrounding structures can be determined. The vein should then be centered on the screen. This allows an external landmark, the center of the transducer, to be established. Pressure over this area with a blunt object, such as a fingertip, can confirm the correct location. The needle should then be inserted at a 45-degree angle to the skin at a distance from the probe equal to the depth of the target vessel (Fig. 6.4). Immediately after entering the skin, the needle tip should be identified on the screen. It will appear as a hyperechoic (white) object within subcutaneous tissue. The needle tip should be followed with the transducer as it advances toward the vein. As the needle tip reaches the vein, the wall of the vessel will be seen to deform (see Video 4). A flash of blood in the syringe confirms that the needle has entered the vein (Fig. 6.5).