How do I assure that my Supraclavicular (& Other) CPNB catheters will be a success?

This post is an adaptation of a question that was emailed to me by Dr Sharanu Patil, an anesthesiologist at SPARSH Hospital in Bangalore, India. Dr Patil has has been using ‘ultrasound only’ techniques for seven years and has regular success utilizing ultrasound-guided single injection supraclavicular nerve blocks, however, he has found that inserting catheters leads to a variability in success. Let’s start with the assumption that, like Dr Patil, you have good fundamental ultrasound skills and can recognize the sonoanatomy and appropriate local anesthetic spread. The problem stated once more is that you find catheter infusions unpredictable or unreliable. That is, when catheters are used, you have primary block success, but secondary block failure.

I will discuss a few common errors that occur with using catheters and some solutions to these problems. For this discussion, let’s focus on using catheters for the supraclavicular nerve block in particular. One of the confounding aspects of catheters comes after the primary bolus is injected. Unless you have a helper that is also sterile (or you have a third arm!), you will have to set down the probe to introduce and advance the catheter. What this means for most people is that although they saw where the local anesthetic spread and recognize that it was appropriate, they 1) do not have a mechanism to confirm with ultrasound that the catheter is inserted correctly, 2) they do not know where the optimal final position of catheter should be, or 3) they do not realize that (even though the needle never moved a millimeter!) the position of the surrounding tissue is often significantly altered just by removing the pressure the probe had on the underlying tissue when you set the probe down. This causes the needle to aim in a different direction relative to the intended target and to catheters being placed too far from the intended location. The needle may still point toward the target, but it will be at a different angle which often has the same effect.

[wlm_private_Member]You can test this last fact by placing your probe on any body part, utilizing the usual amount of pressure that you might use to visualize your target then slowly release that pressure until you barely have a discernible image. You will see veins become apparent, and you will see that the tissue under the probe will elevate a good amount. Scan through the following cartoon slides to see an example of how this might occur with an interscalene catheter. Notice that the needle never moves one bit, but the structures beneath the probe shift upward once the probe is removed.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Here is a caveat regarding this issue. It does not apply to all nerve blocks (if your technique is sound!). For example, if your needle is several centimeters beyond the point where it pierces the fascia iliaca during a femoral nerve block or a fascia iliaca nerve block, the effect of lifting away your probe is generally irrelevant. Not so in most cases for the brachial plexus!

Continuing to address these issues in reverse order, we can address the optimal location for a supraclavicular catheter. Most of the time, the brachial plexus does not extend toward the medial side of the supraclavicular artery much past the 12 o’clock position (toward 2 o’clock or 10 o’clock depending on your orientation). When the plexus is in the typical position, the ‘corner pocket’ is a perfect place for the catheter. Advance the catheter into the convergence of the first rib, plexus and artery with another centimeter or so to allow for shoulder movement. Advancing the catheter a bit further is important if you have a mufti-orifice catheter since the infusion does not come out of the tip of the catheter. Watch that it does not advance under the artery or curl up inside the middle scalene muscle.

If the plexus does advance medially beyond what was previously stated, the corner pocket will miss more of the radial aspect of the patient’s hand if you leave the catheter in the corner pocket. Sometimes, a bolus at a later time will address this problem. An option that can be attempted WITH ULTRASOUND is to press the needle into the middle of the plexus (between 8 or 10 o’clock if medial is towards 3 o’clock), observing for vessels within the plexus and taking care to avoid the direct impaling of a nerve. Often, there are obvious ‘clusters’ that can be pushed away. Also, be careful not to allow the needle to directly aim at the subclavian artery, or it could be punctured. Do not attempt this if there is not clearly visible and distinct borders around reasonably sized neural elements. I will remind you once again that this is an ADVANCED TECHNIQUE and should NOT be attempted by novice practitioners. The catheter can be left within the sheath of the plexus with a few extra centimeters added. It is always reasonable to place the catheter within the space created by the bolus of local anesthetic between the plexus sheath and the middle scalene muscle at the supraclavicular position or at a point between a true supraclavicular and interscalene position. This should typically provide adequate relief from an infusion in this circumstance.

Now, let’s say that you know that it matters to visualize the catheter going into the proper location, and you know the proper location, how do you watch the catheter advance into place with ultrasound without growing a third arm? Beyond having someone else advance the catheter in sterile fashion as you hold the needle and catheter, there are two options. The first option is to position the probe to where you can see the needle and the target and have someone grasp the probe for you from the other side of the drape (and reposition them as needed) and use one hand to hold the needle in place as you advance with the other hand. The assistant’s hand is not sterile, but they are grasping the probe from the non-sterile side of the plastic drape such that only the sterile side of the drape is touching the probe.

The second option, which is my option of choice, is to hold the probe with one hand as you did before and hold the needle and advance the catheter with the other hand. It is too complex to describe in great detail here, but I hold the needle between my 4th and 5th fingers and grasp the catheter between the tips of my thumb and index finger and push the catheter into the needle. All of these options allow you to advance the catheter into proper position with direct visualization under ultrasound which is necessary to ensure reliable catheter position every single time. I will devote another Tip & Trick post to describing this advanced technique in the near future!

I will make just a few further remarks on this subject. If ‘proper’ catheter position is significantly affected by patient movement, which can be another reason for catheter migration and ‘delayed’ secondary block failure, it usually means that the catheter was not optimally placed. Further, inadequate securing of the catheter and techniques related to the dressing can allow for too much ‘back track’ and catheter leakage, and this will likely be a secondary failure (or poorly effective secondary nerve block). Lastly, poor patient evaluation is a common cause of ‘apparent’ secondary block failure. I do not have time to address this final concern, but you can find a great deal on this website on this topic.

I hope this brief discussion is helpful toward your efforts of expanding to continuous peripheral nerve blocks. There are tremendous advantages awaiting your patients as well as to your hospital with the positive financial aspects that will be available to you once you begin to make this transition!

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