CORRESPONDENCE |
Use of a stimulating catheter for femoral nerve block
* E-mail: thomas.volk{at}charite.deEditor—In their paper, Jack and coworkers1 retrospectively analysed the effectiveness of femoral catheters for pain relief after knee replacement surgery and concluded that stimulating catheters are not advantageous in terms of pain levels and opioid consumption compared with conventional catheters.
The rational for using stimulating catheters is based on the assumption that catheter tips are directed close to nerves. The question arises whether nerve proximity is really needed for the femoral nerve to be blocked effectively in routine clinical use. Several reasons argue against this necessity, particularly when larger volumes (40 ml) of local anaesthetic are used.
Firstly, anatomical review suggests that, once the iliac fascia is penetrated, there are no relevant diffusion barriers for local anaesthetics. Secondly, catheters threaded 16–20 cm from the inguinal level radiographically deviated in 77% of cases but were as effective in motor blockade of the femoral nerve, and only marginally less effective in sensory blockade of the femoral nerve, compared with radiographically well placed catheters.2 Thirdly, iliac fascia blocks performed without any nerve stimulation are as effective as femoral nerve blocks, in both children3 and adults,4 suggesting no clinically meaningful reason for placing catheter tips in close proximity to the femoral nerve. Assuming that the authors used the same insertion depth into a ‘femoral nerve sheath’ for both catheter types, that is 3–5 cm, we think that deviation rate would be much lower than those reported by Capdevila. Consequently, one would not expect a relevant difference whether an electrical proximity of the catheter tip is present or not. In this context, it is unclear why the authors accepted higher current thresholds for the stimulating catheters (
1 mA) compared with stimulating needles (<0.5 mA).
When using ultrasound, the tip position can suggest proximity even though sufficient nerve stimulation is not achieved, injection of local anaesthetic usually produces a clinically effective block.
Following this reasoning, the hypothesis that lower morphin consumption and pain scores could be expected in their study is questionable.
Pham-Dang and colleagues5 demonstrated that brachial plexus block catheters, which could not be stimulated, were ineffective and radiographically misplaced. In three sciatic catheters no stimulation was possible, but catheters functioned well, and in the radiography a correct position was present. Hence, it was impossible to stimulate an apparently correct catheter. The inability to stimulate clinically effective catheters in the report by Pham-Dang mainly is a result of using saline for catheter placement.
We agree with the authors, that well designed studies should to be done to prove the superiority of stimulating catheters, but not for the femoral nerve.
Berlin, Germany
* E-mail: n.jack{at}maartenskliniek.nl
Editor—We would like to thank Drs Birnbaum and Volk for raising a number of interesting points. The first is that, considering the anatomy and the good results which may be obtained by a blind technique,4 the results of our study were to be expected. There is some logic to this assertion, and yet so many self-evident matters have not stood up to closer investigation that we consider our study to be useful in the evolving debate about stimulating catheters.
Our catheters were inserted, as they suggest, 3–5 cm, which we consider to be a good balance between preventing dislocation on the one hand and deviation on the other. We accepted a stimulating value through the catheter as high as 1 mA as this was recommended to us by the manufacturers as safe and effective. Placement of the stimulating catheter is not always easy, and repeated attempts are often necessary. In a recently published study, the catheter had to be redirected up to 20 times.6 Repeated attempts to get low values can be uncomfortable for the patient and theoretically could increase the chance of nerve damage. In most of our cases, we were able to use 0.3–0.5 mA of current, but we accepted values up to 1 mA. It is unclear whether the results from the stimulating catheter are improved by only accepting lower stimulating values.
There are still many uncertainties about the value of stimulating through the catheter. We have had cases with excellent stimulation through the catheter and no block, and there are reports of no stimulation but an excellent block.5 Such experiences undermine the need for meticulous catheter placement and of course raise question marks about the whole principle of stimulating catheters. However, it is too early to write off the stimulating catheter as a white elephant. There are studies showing that the placement of stimulating catheters is on average more accurate.7 The clinical effectiveness of the stimulating catheter is not yet clear but we do not agree with their assertion that there is no need for further investigation of stimulating catheters for the femoral nerve. Perhaps the most important comment by Birnbaum and Volk concerns the use of ultrasound to confirm the catheter position. Nerve location by ultrasound will surely become an important tool in regional anaesthesia and may eventually make the whole discussion about the stimulating catheter academic.
Nijmegen, The Netherlands
References
1 Jack NT, Liem EB, Vonhögen LH. Use of a stimulating catheter for total knee replacement surgery: preliminary results. Br J Anaesth 2005; 95: 250–4
2 Capdevila X, Biboulet P, Morau D et al. Continuous three-in-one block for postoperative pain after lower limb orthopedic surgery: where do the catheters go? Anesth Analg 2002; 94: 1001–6
3 Dalens B, Vanneuville G, Tanguy A. Comparison of the fascia iliaca compartment block with the 3-in-1 block in children. Anesth Analg 1989; 69: 705–13
4 Capdevila X, Biboulet P, Bouregba M, Barthelet Y, Rubenovitch J, d'Athis F. Comparison of the three-in-one and fascia iliaca compartment blocks in adults: clinical and radiographic analysis. Anesth Analg 1998; 86: 1039–44[Abstract]
5 Pham-Dang C, Kick O, Collet T, Gouin F, Pinaud M. Continuous peripheral nerve blocks with stimulating catheters. Reg Anesth Pain Med 2003; 28: 83–8[Web of Science][Medline]
6 Morin AM, Eberhart LH, Behnke HK et al. Does femoral nerve catheter placement with stimulating catheters improve effective placement? A randomized, controlled, and observer-blinded trial. Anesth Analg 2005; 100: 1503–10
7 Salinas FV, Neal JM, Sueda LA et al. Prospective comparison of continuous femoral nerve block with nonstimulating catheter-guided perineural placement in volunteers. Reg Anesth Pain Med 2004; 29: 212–20[Web of Science][Medline]
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||