Up to this point I have never had to deal with a difficult to remove peripheral nerve catheter. I was concerned that it had knotted, and since the catheters are supposed to be radioopaque, I asked him to order an Xray so as to determine if there was a knot, or if it appeared to be wrapped around the neurovascular bundle. Unfortunately, the Xray was unhelpful because the catheter had been taped in a tight coil at the insertion site obscuring the portion of the catheter located inside the body. I grabbed the ultrasound machine and viewed the area under US while pulling on the catheter. While the catheter couldn't be viewed easily I could see that the neurovascular bundle "tugged" with each pull of the catheter. Vigorous attempts to remove the catheter met with failure. Thereafter, I placed a 18G tuohy needle over the catheter in an attempt to loosen a potential knott . I failed to successfully guide the needle over the catheter due to catheter flexibility. Finally, I decided to pull until the catheter was removed or it broke. I verified that vigorous pulling on the catheter did not compromise the subclavian artery via ultrasound visualization, injected the catheter with omnipaque so that it could be easily located should the catheter break, and then tugged. I slowly applied greater and greater forced, as close to the end of the catheter as possible. A sudden, pop, was followed by easy removal of the catheter with tip intact and demonstrating a single knot 3 cm from the tip.
I performed a quick literature search to find any studies of this phenomenon. At the Mayo Clinic a large review whas done on nearly 6000 peripheral nerve catheter . They discovered that the inicidence of knotted catheters was 0.13%. Also interesting was that only catheters that had been inserted greater than 8 cm past the needle tip became knotted. Of the 8 catheters that were found to have knotted, 6 were femoral nerve catheters, 1 was a fascia iliaca catheter, and one was an axillary catheter. From this large review, we can surmise that threading catheters greater distances past the needle tip increases the risk of knotting. How much is uncertain as no catheters that were threaded less than 8 cm became knotted in this review. Unfortunately, inserting catheters less than 8 cm will not guarantee avoidance of knotting as there are case reports of knotted interscalene catheters threaded only 2 to 3 cm. Here is a fairly up to date list of published case reports of knotted perineural catheters.
- catheter distance/site: 12 cm (beyond tip) Fem stim catheter-removed with 10 cc saline injection via catheter
- Burgher et al: 8 cases: 8 to 10 cm (beyond tip) fem non stimulating catheter 7 removed with fluoroscopic guidance
- Offerdahl et al. 1 case 10 cm (beyond needle tip) non stimulating catheter removed with simple patient repositioning
- Macleod et al. 1 case: 5 cm (within sheath) non stimulating removed via surgical exploration
- Rudd et al. 1 case 20 cm (at skin) non stimulating catheter removed via surgical exploration
- Motamed et al. 1 casse reported: 14 cm (at skin) non stimulating catheter removed by surgical exploration.
The literature agrees that the first step in the approach to a catheter that is not easily removed is to try repositioning the patient. Particularly in femoral nerve catheters and fascia iliaca catheters, flexion at the hip of up to 90 degrees has proven to be effective in several case reports. Often, tension of the tissues, can result in difficult catheter removal, and repositioning the pateint as to decrease tension of tissues on the catheter will be successful. If this does not work, it makes sense to get an image if you suspect that there is a knot. Although peripheral nerve catheters are labeled radio opaque, there fine structure can make clear visualization dificult. Injecting some omnipaque will improve the visualization and give a better clue as to whether it might be knotted around the neurovascular bundle. Another noninvasive and simple strategy is to inject 10 mL of saline through the catheter prior to further attempts to remove it. Expansion of the fascial plane may enhance the ability to remove a knotted catheter that is otherwise hung up. This was reported in a case report of a femoral stimulating nerve catheter . Visualizing this process via ultrasound can be helpful.
If repositioning, saline injection, and prolonged steady traction fails, there are two other options reported in the literature. Removal with GA and surgical dissection or fluoroscopic guided removal. In the review at the Mayo clinic , they reported 100% success rate (7/7) by inserting a guide wire into the peripheral nerve catheter to give it greater rigidity, and then placing progressively larger dilators around the catheter using fluoroscopy to guide the process. Larger or smaller dilators are used depending on the site of the knot. Of course, if this technique is to be successful, the catheter cannot be knotted around a nerves, arteries or veins.
If the catheter breaks in attemtps at removing it, leaving the distal tip in place is a possibility. However, the close proximity to the nerve can lead to neuralgias from the inflammatory response initiated by a foreign body. Infection can also be a problem. There is a case reports of femoral neuralgia being relieved by removal of a retained catheter peice that had been sheared off because the guide wire from the catheter was removed prior to removing the needle.
1) Burgher AH and Hebl JR. Minimally invasive retrieval of knotted nonstimulating peripheral nerve catheters. Regional Anes Pain Med. 2007;32(2): 162.
2) Kendall M et al. Removal of a knotted stimulating femoral nerve catheter using a saline bolus injection. Local and Reg Anesth. 2010;3:31.