The CDC guidelines recommend placing subclavian lines to reduce the risk of catheter-related bloodstream infections. Meanwhile, mounting evidence suggests that we should probably be placing lines with ultrasound guidance. Unfortunately, the ultrasound-guided subclavian can be tricky. This post describes a slight modification that could make the technique easier and safer.
Theoretical rationale behind the shrug technique
Concept #1. Subclavian is the ideal site
The subclavian has numerous advantages:
- Easier to keep clean and dry, reducing infection risk (O’Grady 2011).
- Lower risk of catheter-associated DVT, compared to jugular or femoral sites (Parienti 2015).
- Avoids tracheostomy ties or neck collars.
- Doesn't impede venous drainage from the brain in neurocritically ill.
- Leaves the right internal jugular free for transvenous pacer wires, hemodialysis catheters, or ECMO catheters.
The main disadvantage is the risk of pneumothorax, which will be dealt with below.
Concept #2. Landmark subclavian isn't a viable solution for a teaching hospital
There are numerous reasons that ultrasound is desirable for central venous access. For the sake of brevity, only one will be discussed here: the Dunning-Kruger Effect. With falling popularity of the landmark subclavian, it is rare for trainees to master it. Most often, they are trained to the point of being dangerous (Mount Stupid, figure above).
Trainees would benefit more by learning to use ultrasound guidance at the ninja level. Ultrasonography has a relatively steep learning curve, so mastery can be reached relatively fast. Furthermore, identical ultrasound techniques can be used at any anatomic location (subclavian, jugular, femoral), allowing the trainee to simultaneously master every type of line insertion (1):
- The long-axis view is difficult in obese patients, when the target vein is deeper from the skin surface (see above).
- Fanning the ultrasound probe back and forth in short-axis can easily provide an accurate three-dimensional understanding of where the needle is relative to surrounding structures. This can allow for easy re-direction of the needle, if its initial direction isn’t perfect.
- Two randomized controlled studies both found the short-axis technique to have a higher success rate compared to long-axis technique for ultrasound-guided subclavian line placement (Vezzani 2017, Maddali 2017). The larger of these studies also found that short-axis technique reduced the risk of arterial injury, likely because it allows simultaneous visualization of the needle, vein, and artery (Vezzani 2017). Similar results have previously been found when cannulating the internal jugular vein (Chittoodan 2011).
- The short-axis view allows you to make sure the needle is aimed right at the middle of the vessel. This promotes successful passage of the wire, rather than hanging up on the edge of the vein:
The drawback of the short-axis approach is that it is possible to lose track of the tip of the needle (visualizing the shaft of the needle rather than the tip). Fortunately, this error is avoidable using proper technique:
- Incrementally advance the ultrasound probe and needle in short steps. Keep moving the ultrasound probe slightly ahead of the needle, then insert the needle to keep up. By walking the needle down towards the vein in this fashion, you are always visualizing the needle tip (not the shaft).
- If you get lost, wiggle the needle slightly while fanning the ultrasound probe back and forth. Find the tip of the needle, then continue.
Concept #4. Ribs can be used to prevent pneumothorax
Ribs run in-between the subclavian vein and the pleura. These can be used strategically to prevent pneumothorax. Senussi 2017 recently published a description of an ultrasound-guided axillary vein catheter placed over the second rib (figure below). The needle is aimed directly towards the rib, so that if it overshoots the vein it will hit the rib.
In neutral position, the clavicle lies over the proximal aspect of the subclavian vein. Shrugging the shoulder pulls the clavicle upwards, out of the way. This opens up a window where the subclavian vein can be seen with ultrasound, with the first rib behind it.
This position and window is ideal for placement of a central venous catheter:
- The subclavian vein is large, making it easy to cannulate and pass the wire.
- Pneumothorax is unlikely for several reasons:
- If the needle goes too far, it will usually hit the first rib (which protects the lung)
- If the needle doesn't hit the first rib, it will often arch over the lung. A medial subclavian puncture overlies the dome of the lung. Unless the needle is pointed downward at a steep angle, it will tend to pass over the lung (more on this below).
- The subclavian vein at this position is generally large. This reduces the likelihood of inadvertently puncturing through the entire vessel without getting blood return.
- Shrugging the shoulder increases the angle between the subclavian vein and the brachiocephalic vein as shown below. This may promote passage of the wire and catheter down the brachiocephalic vein (rather than taking an undesirable turn into the internal jugular vein).
- Compared to axillary vein insertion, more proximal catheter insertion might reduce the risk of thrombosis (Buzancais 2016).
#1. Site selection
The left subclavian vein is usually preferable for the following reasons:
- Lines placed in the left subclavian are less likely to be malpositioned (Tarbiat 2014, Boon 2007). The right subclavian makes a sharp turn when merging with the internal jugular (figure above), which can promote malposition. In contrast, the left subclavian takes a diagonal glide path directly into the superior vena cava, without any sharp turns. This also explains why the left subclavian site is favored for placement of transvenous pacemakers or Swan-Ganz catheters.
- A 20-cm central line can generally be advanced to the hilt on the left side without risking placement in the right ventricle (unless the patient is unusually small). Advancing the catheter completely allows it to be secured with only two sutures and a small dressing, which keeps things neat and reduces the risk of infection.
Of course, the right side may be preferred in some patients (e.g. unilateral right-sided lung disease).
#2. Patient positioning & adequate vein length
Ensure with ultrasound that the target is large enough to cannulate and wire. If the target vessel looks small, consider the following maneuvers:
- Trendelenburg position.
- Shrugging the shoulder more may help open up the ultrasound window better.
Just because it is possible to get a view of the subclavian vein doesn't mean that the procedure is safe. You should be able to obtain vision of the subclavian vein over a couple centimeters with the probe oriented vertically (as it would be during the procedure itself). This is usually easy, but it can be impossible in severely obese patients. If you can't achieve a good landing zone, choose another site (e.g. the internal jugular).
The patient should maintain this shrugging position for the entire procedure. If the patient changes position before insertion of the dilator, dilation may be difficult (because you will be trying to dilate a non-linear tract).
#3. Target selection – Avoiding the lung
- Bone: There is often a considerable length of subclavian vein which is overlying the first rib. This is an ideal target for cannulation, because the rib blocks the needle from potentially causing a pneumothorax.
- Medial soft tissue sign: Very close to the sternum, you may encounter a view where the vein is overlying soft tissue. This is a reasonable site for cannulation. The soft tissue will provide you with some buffer if you advance too far. Furthermore, in this location you're often overlying the dome of the lung such that you cannot hit the lung (the needle will arch over the lung tissue into the mediastinum; figure below). Use caution, however, because if you go exceedingly deep there is a risk of injuring mediastinal structures.
- Vein directly overlies pleura or subclavian artery: Try to find a safer view elsewhere.
Ultrasonography provides two-dimensional images. However, by scanning back and forth you can combine these images in your mind to generate a three-dimensional understanding of the vein and surrounding anatomy. Identify dangerous structures (subclavian artery, lung) and avoid them.
#4. Needle insertion
The needle should be inserted with caution and precision. Even if bone is underlying the subclavian, do not rely on the bone to prevent injury. The first and best line of defense against complication is precise control of the needle tip. The most important technique here is coordinated advancement of the needle and ultrasound probe in small steps, with the ultrasound probe always ahead of the needle (discussed above).
Another trick is helpful here. Ideally the linear probe should be perfectly aligned along the axis of the target vessel (figure below). If the probe and vessel are aligned, then it's OK if you enter the vessel at a slightly different spot than you were initially aiming for (your needle will remain on track to hit the vessel whether the needle takes a slightly sharper or shallower angle). Alternatively, if the probe and the vessel are misaligned then it is easy to miss the vessel if you miscalculate the depth of your needle slightly (the vessel veers out of the pathway of your needle).
A simple way to make sure that your probe is aligned with the vessel is the fan test. Fan the transducer back and forth slightly. If the vessel is aligned correctly, it will stay in the center of the ultrasound screen. If the vessel is misaligned, it will shift left and right on the screen. If misaligned, take a minute to rotate the probe until it is aligned with the vessel.
Threading the wire is occasionally tricky. Sometimes the wire will veer into the internal jugular vein or the contralateral subclavian vein. This may be suspected when the wire initially passes smoothly but then hangs up around a depth of ~15 cm.
Delayed wire hang-up can often be resolved by using the plastic introducer catheter to hold position in the vein and then re-inserting the wire a few times (similar to the concept of re-floating a pacer wire). With some trial-and-error (e.g. rotating the head towards the operator, the Abesh manevuer, inserting the wire with the J-tip pointing in a different direction) the wire can often be encouraged to pass more smoothly. If the wire repeatedly hangs up ~15 cm the central line can still be placed and often will be OK (either lying in the superior vena cava or contralateral subclavian, which is generally adequate).
#6. Passage of the central line
For patients with severe obesity, this can be tricky. There may be several centimeters of tissue between the skin and the vessel. If the catheter is advanced too abruptly, it can herniate into the soft tissue and end up outside the vessel:
- Gently compress the soft tissue as you advance the catheter. This reduces the distance that the catheter needs to pass through the soft tissue before entering the vein.
- Feed the catheter in gently.
- Occasionally palpate to ensure that the catheter isn't looping within the soft tissue.
#7. Catheter depth
This depends on three factors:
- Patient height
- Amount of soft tissue between the skin and the vein (increased in morbid obesity). For patients with excess soft tissue, the line should be placed deeper, to prevent being pulled out of the vascular system by movement of the soft tissue.
- Location in the right versus left subclavian.
In most cases, a left-sided subclavian can be advanced to the hilt (using a 20-cm catheter). This may result in the line tip sitting in the atrium, which is fine. For patients who are short and thin, a depth of ~18 cm may be better on the left side (this can still be secured using two sutures, without a lot of line flopping around). A right-sided subclavian will need to be advanced less (perhaps ~2-3 cm less deeply than on the left side).
#8. Quality control
The goal shouldn't be to perform competent procedures, but rather to perform flawless procedures. If you shoot for flawless and fall short, you'll still be doing an excellent job. Every single procedure should be critiqued using the following metrics:
Indicators of high quality:
- Low number of needle passes.
- Needle-tip control is so meticulous that you can see exactly when the needle is about to enter the vessel (e.g. you see it tenting the proximal vessel wall before it pierces though, then you watch it pop into the vessel).
- Needle enters the center of the vessel, allowing guidewire to pass easily.
Indicators of low quality (2):
- The first sign that you are in the vessel is a flash of blood in the syringe. Ideally you should already know that you're in the vessel based on ultrasonography, before blood enters the syringe (#2 above).
- The needle accidentally passes through the vessel and crashes into the first rib. This is a sign of very poor technique, with the needle-tip outrunning your ultrasound probe.
- You puncture through the entire vessel without realizing it, and only obtain blood return when pulling back the needle.
Obviously, every procedure won’t be perfect. The key is continuously critiquing technique and aiming for perfection. Don't be satisfied merely by performing the procedure successfully.
Genius General experience
The shrug line has been in use at Genius General Hospital for over a year. It has likely been placed about a hundred times, mostly by pulmonary fellows. A couple catheters were malpositioned into the subclavian or internal jugular veins, which is an inevitable consequence of subclavian catheterization (catheters inserted into the contralateral subclavian vein were left in situ and used without problems)(3). One catheter was inserted in subcutaneous fatty tissue as described above (see #7), and this was removed without sequelae. No hematoma, hemothorax, pneumothorax, or other serious complications occurred. Procedural difficulty was mostly limited to patients with severe obesity (although in such patients it is generally possible for an expert operator to place the line)(4).
- The ultrasound-guided subclavian is a widely recommended and well-accepted procedure. The shrug technique represents a minor modification on this procedure, which may improve speed and safety.
- Shrugging the shoulder upwards opens up a proximal window where the subclavian vein can be visualized and cannulated.
- The success of this procedure may be easily estimated before starting, using ultrasonography. If the views are of dubious quality, try finding a better site.
- The ultrasound-guided subclavian central line placement depends on very precise ultrasound-guided needle control, so this isn’t a novice-level procedure. However, this is a technique well worth learning. Once mastered it will allow the operator to place any central line with ease (subclavian, jugular, or femoral).
- A similar argument can be made for anyone who isn’t constantly putting in central lines. For example, many attendings at training hospitals may put in 25-50 lines per year. If these are all placed in the same technique, it will be easier to maintain competency in that single technique. If these lines are divided between three or four different techniques, it will be difficult to maintain competency in all of the different techniques.
- Please note that “low quality” indicators are still compatible with a safe and effective line insertion procedure without any harm to the patient. However, if you are consistently hitting low-quality indicators, that suggests that your technique needs work.
- It's debatable whether a central line in the contralateral subcalavian vein needs to be replaced. If the catheter isn't being used for anything really irritating (e.g. chemotherapy, hydrochloric acid, TPN) then it is probably fineto leave it in place and use it. For any individual patient the risk of repositioning the line (increased infection) or inserting a new line must be weighed in comparison to the risk of using the catheter in situ (which seems to be negligible).
- An ultrasound-guided subclavian isn't the recommended site for a patient with supermorbid obesity. However, patients are encountered without other good options (e.g. internal jugular veins are occupied with a hemodialysis catheter, stenosed, or clotted).
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