First, what are the complications, and how common are they?
When speaking about complications in regional anaesthesia many think about serious incidents, leading to severe morbidity and even mortality. Fortunately such complications are very rare. Examples are persistent nerve damage and local anaesthetic systemic toxicity (LAST). Given the small numbers of such complications, the many different nerve block catheters that could be placed, and the very different patient factors involved in each case it is difficult to find any exact statistics on the subject. I think it is enough to know that those risks are small, only slightly larger than for the respective single-shot blocks.1,2 The same is true for risks of bleeding, and thereby issues of coagulation deficits. Risks for wrong-sided blocks should also be comparable with single-shot blocks. The risk of infection due to a peripheral nerve block catheter is comparable to the infection risks for epidural catheters, only farther away from the neuraxis. The same sterility guidelines should be adhered to. Here I will instead focus on complication risks that completely differ from single-shot blocks and the epidural catheters.
Perhaps the most devastating of complications can happen when we insert a peripheral nerve catheter but it enters the spine through the intervertebral foramen and turns into an epidural catheter or even an intrathecal catheter without us knowing. This is definitely rare, but it has happened multiple times, for interscalene block3, paravertebral blocks and for lumbar plexus blocks. Doing nerve block catheters in such areas you must know about this risk. Directing the needle towards the spine should be avoided, and threading the catheters extra distance inwards should mostly also be avoided.
When and where to inject the local anaesthetic?
Giving a large dose of local anaesthetic in the catheter when it is positioned and secured is a good routine to have, but divide the full dose in smaller aliquots over a few minutes. If the above situation has happened and we are getting an epidural or even intrathecal effect it is much better if it happens in the operation theatre or PACU than on the ward. Of course this also safeguard against the catheter tip having entered a vessel and causing a LAST reaction.
I even go a bit further in this thought, in that I recommend all colleagues to not give any local anaesthetic at all via the needle, except for skin infiltration via a smaller needle. Other than that I use only saline until I’m satisfied with the position of the catheter. The reason for this is the most common complication of all when it comes to continuous nerve blocks, namely that we cannot trust the catheter to work. Even if the needle tip was in the correct place the catheter might not end up correctly. Had I given the LA through the needle I would then still have good analgesia in OR and PACU, but the patient could get break-through pain on the ward 6–10 hours later. By only giving LA via the catheter I will know during surgery and in PACU whether the catheter will work or not. Then it’s much quicker and easier to redo the catheter insertion, or time enough to switch to some other form of analgesia if that is deemed best. Predictability is key!
The catheter often stops functioning even if it was correctly placed from the beginning.4 It could happen in 20–30% of the patients within the first 24–48 hours. However the numbers are difficult to interpret. Studies are with many different nerve blocks. Some measure the usage of rescue medication as an endpoint and take that as an indication for catheter failure which it might not be. Other only look at the spread of injectate around the nerves in volunteers. Few studies are done with comprehensive sensory and motor testing of the nerves that should be blocked by the catheter. Early catheter failures could of course be catheters that were incorrectly placed from the beginning. Later failures could be due to movements in the tissues causing the catheter to move internally, or poor fixation leads to movements at the level of skin penetration. Whatever the reasons and the numbers, most experts agree that catheters often do not function for as long as we would hope for. Some argue that perhaps the time of the nerve block catheter is over. With adjuvants such as dexmedetomidine and dexamethasone most single-shot blocks can be made to last for approximately 24 hours, and if needed the patient could return the next day for a similar block once more. On the other hand, there are institutions where continuous nerve blocks are working very well.2
My tips and tricks on peripheral nerve catheters
Choose wisely which catheters to actually place. One favourite could be the rectus sheath block where you can insert the catheter several centimeters extra, creating a large margin of error. Another good example would be the femoral nerve block. Holding the transducer transversally, and inserting the needle in-plane from lateral to medial you can puncture the skin quite laterally, pierce the fascia iliaca in the lateral part of the iliac muscle and then hydrodissect just beneath the fascia iliaca as you near the femoral nerve. Continue hydrodissecting until the needle tip is on the medial side of the femoral nerve. Then when you insert the catheter the margin of error is also quite large. If it is accidentally retracted a few cm it should perhaps be called a fascia iliaca catheter instead, but it would still block the femoral nerve.
Catheters in places where skin, muscles and nerves move in relation to one another are always more prone to displacement. Also plastic dressings, tapes and other securing devices often come off in such places. An example of that is the interscalene brachial plexus (ISB). Each time the patient moves his head there’s a risk that the catheter moves. The same can be true for the popliteal sciatic block when the patient bends the knee. Inserting the popliteal catheter only a few centimeters more proximal than the usual single shot, or the interscalene catheter a few cm more caudal than the ISB single shot can lead to much more secure catheters. Theoretically the ISB catheter should then perhaps be called an upper trunk catheter instead, but the endpoint of analgesia to the shoulder would still be met.
For nerve block catheters to larger plexuses like the infraclavicular I do as with the femoral, ie I try to get into the plexus early in the passing of the needle and then hydrodissect as far as I can through the plexus before inserting the catheter. Then I get that margin of error. For blocks such as the popliteal sciatic or the adductor canal block I start visualizing the structures transversally, but before inserting the needle I rotate the transducer approximately 30–60 degrees and do the needling in-plane with the transducer. That makes round structures look oblong, but it is still quite easy to separate them from each other. If in doubt I can always switch between this oblique view of the nerve and the usual transverse view. This, I think, is easier than to change completely and do the block out-of-plane when I am used to do the respective single shot block in-plane. Inserting the catheter is said to be easier when doing the needling out-of-plane, but I believe I get almost the same angle to the nerve this way.
After inserting the catheter, rather a few centimeters too far than too short, I use ultrasound to verify that the catheter is in a correct place. It does not stay in the exact plane of the ultrasound beam, but combining minimalistic tuggings in the catheter with dynamic movements of the transducer to visualize the target and the surrounding tissue I can usually get clues as to where the catheter tip is located. Small test injections of saline can then be visualized by ultrasound, perhaps after bit by bit withdrawal of the catheter. It is not necessary to see the exact course of the catheter.
One easy way to start with peripheral nerve catheters is to let the surgeon insert them. In cases of amputations there might be a large nerve that the orthopedic surgeon can insert the catheter into. I have used it both in midfemoral amputations (sciatic) and forequarter amputation (brachial plexus) with good effect (unpublished). Rectus sheath catheters and TAP block catheters have been described in the same manner.
Securing the catheter There are many specific catheter fixation devices on the market. I prefer using histoacrylic glue which both acts to hold the catheter fixated to the skin a few cm around the insertion site, and prevent leakage of fluid around the catheter. Over the glued catheter I put a plastic film and finally secure all loose catheter and the filter with ordinary tape. Tunneling the catheter is a method that is used by many to secure it better.
New needles and catheters
In later years there have been introduced a few catheters that are designed not to be inserted through a needle. (Examples include Pajunk E-Cath, B Braun Contiplex C and Ferrosan Certa Catheter) That means that they don’t glide that easily in and out of the point of skin insertion. Also the leakage is much reduced, altogether lowering the risk of catheter failure. Some have found these useful. Personally I have found that the technique of inserting these catheters is very different than the ordinary catheter through-the-needle approach that every anaesthetist is used to from epidurals. That difference would probably cause other problems instead, leading to more primary catheter failures, unless you do very many nerve blocks with those new catheter types and learn to master the technique.
Conclusion Nerve block catheters are tricky to master but can be effective.
Ilfeld BM, Continuous Peripheral Nerve Blocks: A Review of the Published Evidence. Anesth Analg 2011;113:904–925.
Walker BJ, Long JB, De Oliveira GS, et al. Peripheral nerve catheters in children: an analysis of safety and practice patterns from the pediatric regional anesthesia network (PRAN). Br J Anaesth 2015 Sep;115(3):457–62.
Gaus P, Heb B, Tanyay Z et al. Epidural malpositioning of an interscalene plexus catheter. Anaesthetist 2011 Sep;60(9):850–3.
Hauritz RW, Hannig KE, Balocco AL, et al. Best Pract Clin Res Anaesthesiol. 2019 Sep;33(3):325–339.
Huang SY, Wang CC, Chang WK, et al. Intravenous propofol precipitates the hypotension induced by inadvertent epidural thiopental injection. Acta Anaesthesiol Taiwan 2006;44:239–42.
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