In Reply:—

I thank Dr. De Tran et al.  for sharing their experience and insights. With regard to their criticism: I did not advocate “inserting the catheter 5–10 cm past the needle tip for nonstimulating . . . catheters.” Because I have little personal experience with nonstimulating catheters, I was merely reflecting what the authors who I cited typically do. I agree that the optimal distance of catheter advancement is speculative at this stage of our knowledge, but the catheter that I typically use (StimuCath; Arrow International, Reading, PA) is an armored catheter, which is floppy when the stylet is removed. The stylet goes down the catheter almost all the way but ends 5 cm from its tip. That, plus my experience of not having any problems with 3- to 5-cm catheter advancement, has led me to believe that 3–5 cm is probably appropriate. I am eagerly awaiting the results of the study planned by Dr. De Tran and colleagues in this regard.

The belief that the perineural sheath can be dilated with small amounts of saline has not yet been validated by research. In fact, we tried to demonstrate this on the perineural tissue of anesthetized pigs under direct vision and could only show that the tissue became edematous and the nerve stimulation was lost, making stimulation via  the catheter useless. However, if practitioners still subscribe to this belief, I suggest that they use 5% dextrose in water to “open up the space” so that nerve stimulation is still possible.1Research is ongoing to evaluate this notion.

I share the author’s sentiments regarding stimulating catheters.

It would be interesting to know for what blocks the 81 catheters of which 70% were found to be coiled up were placed. Based on my own experience, I share the belief that most catheters coil up, but like Dr. De Tran et al. , I do not have any objective data for my belief. It does seem that close to 100% of paravertebral catheters coil up, whereas a relatively small number of femoral catheters do. I am anxiously awaiting the results of their studies. I do believe, however, that the coiling is of no consequence as long as it does not involve too much of the catheter (advanced more than 5 cm), and its tip, where the drug comes out, is in the same fascia compartment as the nerve. This may be a problem with multiorifice catheters, because most of the drug comes out the most proximal orifice.

Ensnaring a nerve in the coil is at this stage only a theoretical possibility because, to the best of my knowledge, no such case has yet been reported in the literature.

We tunnel all catheters, and I agree with Dr. De Tran that it should probably be done routinely.

I share Dr. Swenson’s enthusiasm for ultrasound as a promising “emerging technology” to aid in peripheral nerve blocks. I did not have any access to the unpublished results of Dr. Swenson and his students, and I am eagerly awaiting their publication. Surely, my omission of these results cannot be regarded as a flaw in my article.

I have reread the excellent articles by Marhofer et al. , Chan et al. , and Sandhu and Capal (Dr. Swenson’s references 2–6), and I was again struck by the finding that all five of these reports were on single-injection nerve blocks. Not unlike the rest of the literature, they do not address continuous nerve blocks by ultrasound guidance. I would respectfully remind Dr. Swenson that the title of my article was “Perineural Infusion  of Local Anesthetics” and not “Perineural Injection  of Local Anesthetics.”

Based on the current state of our knowledge, it seems clear that for nerves that are “deep” (and it is not uncommon for us to do subgluteal sciatic nerve blocks where the nerve is 15 cm or deeper, although around 8 cm is the rule), the ultrasound technology simply does not help us much. I therefore believe that my statement that ultrasound helps us the most when the nerve is superficial, and the least when the nerve is deep, is factually correct. The experts cited by Dr. Swenson all restricted their studies to superficial nerve blocks.

With the equipment currently available to us, one needs at least three educated hands to place a catheter with ultrasound guidance: one to hold and maneuver the ultrasound probe, one to hold and maneuver the needle, and one to hold and maneuver the catheter. It is hoped that the emerging technology will address this problem soon.

Most ultrasound experts that I discussed this with (some cited above) agree that a combined technique of finding the nerve with the ultrasound and needle and then placing the catheter with a nerve stimulator is optimal at this stage of our development. Most would not rigidly transform to using only ultrasound guidance for catheters at this stage.

Finally, one of the experts cited by Dr. Swenson has as recently as July 2006 written, “Unfortunately ultrasound cannot help to guide the catheter into the sheath compartment. Because catheters generally curl up as they are advanced, multiple cross sectional views of the catheter are captured on ultrasound; thus the position of the catheter tip cannot be determined accurately.”2With nerve stimulation, there is no problem in accurately determining the position of the catheter tip.

Drs. Chelly and Casati raised some interesting issues. The worst technique for continuous nerve block will have exactly the same outcome as the best technique, in terms of postoperative pain, if not all of the nerves that innervate that joint are blocked and the patients also receive effective multimodal analgesia. The studies that demonstrated no difference between stimulating and nonstimulating catheters were all performed on femoral nerve blocks for knee3and hip4surgery, ignoring the other nerves that innervate the knee and hip joints. Similarly, for example, the best continuous musculocutaneous nerve block will fare the same as the worst musculocutaneous nerve block if pain in the elbow is the measured outcome after elbow surgery and the patients receive effective multimodal analgesia. Therefore, it is not surprising that when stimulating and nonstimulating catheters were compared, the former have consistently been superior in studies where the block had a chance of being successful as the sole block, such as popliteal block for foot and ankle surgery.5,6Finally, the volunteer study was pure and the results were valid, because it tested the motor and sensory functions of only the nerve that was blocked without the obscuring factor of pain due to other unblocked nerves. In the estimation of Dr. Chelly, up to 80% of patients have a sciatic nerve component after total knee arthroplasty.

Although continuous lumbar plexus block may be of value for acetabular fracture and primary total hip replacement, recent studies have shown that pain after the latter is mild (visual analog scale score 3–5 out of 10) and only significant for the first 24 h.7That is probably because the entire joint capsule is typically destroyed during primary total hip replacement, which in effect denervates the hip and explains why patients commonly have more pain before than after the surgery. Furthermore, the hip joint gets its innervation from the entire lumbosacral plexus; therefore, blocking only the lumbar part of the plexus would clearly not be sufficient for painful hip surgery such as acetabular fracture, whereas any block should be sufficient for primary total hip replacement, because there is only mild and short-lived pain in the first place. Based on these two facts, I prefer to do a combined spinal–epidural for hip surgery. The epidural catheter is removed the day after surgery, because most patients usually do not need it anymore and that is typically when the warfarin or other anticoagulants are started. The epidural infusion can also block the entire lumbosacral plexus.

I agree with the sentiments of Drs. Chelly and Casati regarding anticoagulation and continuous peripheral nerve blocks. Unfortunately, when the consensus guidelines were formulated by the American Society of Regional Anesthesiologists task force, they stated, “. . . the Consensus Statements on Neuraxial Anesthesia and Anticoagulation may be applied to plexus and peripheral techniques.”8An important factor that stimulated the development of continuous nerve and plexus blocks was precisely the growing popularity of low-molecular-weight heparin, and I am eagerly awaiting the publication of the “several thousand patient experiences” referred to by Drs. Chelly and Casati to strengthen the overdue case against this statement in the American Society of Regional Anesthesiologists consensus document.

Even if the estimate of Drs. Chelly and Casati that 80% of patients need a sciatic block after total knee arthroplasty were correct (in my experience it is closer to 20%), it would mean that 20% of Drs. Chelly and Casati’s patients (80% of my patients) would receive a nerve block that they do not need. I therefore offer our patients postoperative sciatic nerve blocks if they need it. That would mean that 100% of the patients who received the sciatic blocks actually need them. Furthermore, my experience is that single-injection sciatic nerve blocks are long-lasting blocks as opposed to the posterior knee pain of total knee arthroplasty, and surgeons get nervous if the inevitable “foot drop” persists.

Although I agree that ropivacaine is a better choice than bupivacaine, bupivacaine is much cheaper than ropivacaine and quite suitable when patients cannot afford the more expensive drug.

The University of Iowa, Iowa City, Iowa.


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