The Subclavian Line

Introduction

One of the bread and butter procedures in emergency medicine is central venous catheterization.   There are multiple different central venous access points in the human body, and many may suggest that ultrasound guidance provides the best shot at success given the direct visualization.  The subclavian vein is difficult to visualize with ultrasound, making it better utilized with a landmark technique.  A recent EMCrit blog post1 (here) points out the Dunning-Kruger effect as cognitive bias in relation to an emergency medicine trainee and competence of landmark subclavian venous access.   However, this blog post will highlight one particular landmark-guided central venous access that has a series-reported success rate (without major or minor complications, in mechanically-ventilated patients) at 88.9%: the supraclavicular approach to the subclavian vein.2

Anatomy

Let’s take a stroll back to the first year of medical school, but without the unforgettable smell of formaldehyde products.

The subclavian vein arises from the upper extremities, crossing under the clavicle at the medial to proximal third of the clavicle.  It joins the internal jugular vein to create the innominate, or brachiocephalic, vein.  The subclavian artery is posterior and superior to the brachiocephalic vein.  On the left, it is good to remember the thoracic duct of the lymphatic system joins at the junction of the creation of the left innominate vein (Figure 1).  The domes of the pleura are posterior and inferior to the subclavian veins.  Tintinalli provides a great, simplistic rendition below in Figure 2.

The goal with the supraclavicular approach is to cannulate the superior portion just before it joins the internal jugular vein to form the innominate or brachiocephalic vein.

Of the two, the left subclavian vein may be easiest to cannulate as the right subclavian vein makes a sharper turn when merging with the internal jugular vein, making successful cannulation slightly more difficult1.  That said, on the right side there is a lower pleural dome, more direct route to the superior vena cava and the absence of the thoracic duct, making it the preferred site for less risk of adverse events3.

 

Figure 1.

fig 1

 

(http://geoface.info/aecb/e55783d6c3d6/subclavian-vessels-003d50)

 

Figure 2.

fig 2

 

Procedure and Landmarks

In order to be successful with cannulation of the subclavian vein using the supraclavicular approach, correct identification of the clavisternomastoid angle is needed.  This is formed by the junction of the lateral head of the sternocleidomastoid muscle and the clavicle, as identified in Figure 33.  Rotation of the head towards the opposite side and raising the patient’s head will make this landmark more apparent, and Trendelenberg position will help distend the vein3.

A central venous catheter kit is obtained, and prepared in the usual sterile fashion.  The needle is inserted 1 cm lateral to the lateral head of the sternocleidomastoid mastoid and 1 cm posterior to the clavicle.  The needle is directed at a 45 degree angle to the sagittal and transverse planes, and 15 degrees below the coronal plane, aiming the point of the needle toward the contralateral nipple.  The needle should bisect the clavisternomastoid angle as it is advanced towards the junction of the subclavian and internal jugular veins.

 

Figure 3.

 fig 3

Advantages

There seem to be numerous advantages to this landmark-guided central venous access.  According to the EMCrit blog post mentioned earlier, the CDC recommends subclavian lines as a reduction in risk of catheter-related bloodstream infections.  In part, this could be because it is a relatively clean location anatomically and it is easily cared for by medical staff1.

Dr. Megan Stobart (@Megsahokie), one of the assistant program directors at Einstein who frequently performs this central line with residents, feels like this is “an excellent line especially as a single provider in critical patients”.  As the single provider, you are often at the head of the bed taking care of the airway, and easily can slide to provide central access in the same position.  Additionally, this site can be accessed without guidance of ultrasound, which may not be readily available in some instances.

Dr. Stobart mentions that the direction of the needle should be just medial to the apex of the lung, making complication of pneumothorax less likely.  The landmark for the entrance of the needle also makes hitting the subclavian artery less likely4.

 Disadvantages

 There are some instances where this approach would not be the most ideal, including a patient that cannot lie down flat or in the Trendelenberg position, a patient with a coagulopathy should the artery be accidentally punctured as it is not a compressible site, or a patient that has significant trauma to the area4.

Patient anatomy may be a factor, including muscle spasm or contracture of the neck making one side more difficult to cannulate than the other, known vasculature anomalies and obesity.

Summary

Central venous lines are one of the most common procedures in emergency medicine and are employed in a variety of clinical settings.  Based on multiple variables, there is not a universal site an emergency physician should access, but the physician should take into account the patient as a whole and the clinical scenario when choosing the site.  If the patient does not meet any contraindications, a supraclavicular line should be considered.  This method should be taught in emergency medicine residency programs to arm the resident with the ability and skills to perform this life-saving line in a variety of settings, including that without an ultrasound.  When prepared, the physician can perform this line using anatomical landmarks without as much risk of adverse events.

 

 

References

  1. Farkas, J. PulmCrit- Shrug Technique for US-guided subclavian lines. https://emcrit.org/pulmcrit/shrug-subclavian/ Online Access April 24 2018.
  2. Tomasz Czarnik, Ryszard Gawda, Tadeusz Perkowski, Rafal Weron; Supraclavicular Approach Is an Easy and Safe Method of Subclavian Vein Catheterization Even in Mechanically Ventilated Patients: Analysis of 370 Attempts. Anesthesiology2009;111(2):334-339. doi: 10.1097/ALN.0b013e3181ac461f.
  3. Patrick SP, Tijunelis MA, Johnson S, Herbert ME. Supraclavicular Subclavian Vein Catheterization: The Forgotten Central Line. Western Journal of Emergency Medicine. 2009;10(2):110-114.
  4. Tomar GS, Chawla S, Ganguly S, Cherian G, Tiwari A. Supraclavicular approach of central venous catheter insertion in critical patients in emergency settings: Re-visited.  Indian J Crit Care Med [serial online] 2013 [cited 2018 Aug 24]; 17:10-5. Available from: http://www.ijccm.org/text.asp?2013/17/1/10/112145

 

 

FOAMed Resources

 

Shrug Technique for US-guided Subclavian Lines – Pulm Crit

The Basics – Central Venous Catheters– Life in the Fast Lane

A video showing one method of the supraclavicular approach – Critical Points

 

—Author:  Alexis Cates D.O PGY4  @acates

 

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