The Speed of Sound

Abstract

Image 1. Placement of the ultrasound transducer in the transverse orientation to begin a survey of the venous anatomy.Image 2. Ultrasound image of the internal jugular vein and carotid artery in the transverse plane. The internal jugular (IJ) is typically more oval in shape when compared with the rounded, thicker-walled carotid (C).Image 3. Placement of the cannulating needle for “in-plane” access of the subclavian. As the needle enters at the end of the transducer, rather than at its mid-point, the entire needle (including the needle tip) can be visualized as it travels toward the vein. Sterile technique has been omitted for this demonstration, but should be used during this procedure.Image 4. Corresponding view seen under ultrasound guidance. As the needle enters from the end of the transducer, the entire length of the needle is seen as it travels toward the vein. This image is also available as Video 3 on the EMN website. (See FastLinks.)Ultrasound guidance in supraclavicular subclavian vein (SCV) catheterization is a relatively new concept. Traditional infraclavicular SCV catheterization is poorly amenable to ultrasound guidance because of the overlying clavicle, which can make visualization and direct guidance difficult. Supraclavicular SCV catheterization for central line placement has several advantages: practicality in cardiopulmonary arrest, decreased incidence of central line infections, lower risk of pneumothorax, and decreased incidence of thrombosis. The patient should be placed in a neutral supine position with or without Trendelenburg positioning. The anatomy should be surveyed with ultrasound to identify the SVC before beginning the procedure. Place a high-frequency transducer in the transverse orientation just lateral to the trachea to identify the internal jugular vein. (Image 1.) The internal jugular is typically slightly lateral to the carotid artery, is oval or triangular in shape, and may vary in size with respiration or Valsalva maneuvers. (Image 2.) Once the internal jugular is identified, follow it inferiorly to the supraclavicular fossa to identify the point at which it meets the SCV. (See FastLinks for videos demonstrating this technique.) Angling the transducer anteriorly will facilitate this identification, and the SCV will be seen in its longitudinal orientation as a tubular structure. (See FastLinks for additional images online.) Care should also be taken to identify the subclavian artery, which lies slightly deeper and more posterior to the vein. The subclavian artery is pulsatile, and application of color or Doppler flow can be used to differentiate the vessels. Identifying both vessels helps to assure the physician that the vein is cannulated instead of the artery. Once the subclavian vein is identified, the central venous catheter may be placed by dynamic ultrasound guidance. The introducer needle is advanced with gentle negative pressure from the end of the transducer. (Image 3.) This “in-plane” approach allows the operator to visualize the needle and needle tip at all times while advancing toward the vessel. (Image 4; see FastLinks for another video demonstrating this technique.) The needle tip will be seen to pierce the wall of the vessel and a flash of dark blood in the syringe will confirm that access has been obtained. Once venous access is achieved, the remainder of the procedure is performed via the usual Seldinger technique. Ultrasound can also be used to confirm correct wire placement in the SCV. (See FastLinks for additional images online.) Click and Connect! Access the links in EMN by reading this issue on our website or in our iPad app, both available onwww.EM-News.com.FastLinks BONUS! See One, Do One: This article also appears in the EMN Breaking News Blog with three videos and additional images demonstrating these techniques. Visit http://bit.ly/EMNBreakingNews. Read Dr. Butts' past columns at http://bit.ly/ButtsSpeedofSound. Comments about this article? Write to EMN at [email protected]. Questions? We Have Answers Have an ultrasound question? A topic you'd like to see in future Speed of Sound columns? Send your questions and suggestions for Dr. Butts to [email protected].