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One size does not fit all: Proposal of an algorithm for the practice of ultrasonography in combination with nerve stimulation for peripheral nerve blockade
- Hervé Bouaziz, Denis Jochum, Attila Bondàr, Laurent Delaunay , Michael Egan , Hervé Bouaziz (9 September 2009)
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Author's Reply
- Matthew S. Abrahams, Michael Aziz, Jean-LouisHorn (14 August 2009)
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One size does not fit all: Proposal of an algorithm for the practice of ultrasonography in combination with nerve stimulation for peripheral nerve blockade
- Hervé Bouaziz, [Denis Jochum], [Attila Bondar], [Laurent Delaunay], [Michael Egan], [Hervé Bouaziz] (7 August 2009)
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More studies evaluating inexperienced ultrasound users are now needed
- Colin Sinclair, Colin J.L. McCartney (14 April 2009)
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Meta-analysis for Ultrasound v PNS - the final curtain
- Andrew T Wilson (1 April 2009)
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Author’s Reply: Our review will not change the facts, it has only reported them
- Matthew S. Abrahams (1 April 2009)
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A questionable review will not change facts about neurostimulation compared to ultrasound technique
- Jose Aguirre, Philipp Ruland, Georgios Ekatodramis, Alain Borgeat (12 March 2009)
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Hervé Bouaziz , Denis Jochum, Attila Bondàr, Laurent Delaunay , Michael Egan , Hervé Bouaziz
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Several articles have been published recently comparing the use of ultrasound (US) to that of peripheral stimulator (PNS) as nerve blocking techniques. We have read the meta-analysis by Abrahams et al. of randomized controlled trials, which suggests the greater efficacy of US compared to PNS [1]. Though there are many interesting points to the meta- analysis, Abrahams acknowledges in Appendix A of his review and in the subsequent correspondence, that of the 9 studies used, 3 used an inappropriate motor response as an endpoint and others opted for too high a minimal stimulating current [1]. These practices greatly reduced the effectiveness of nerve blocks using PNS. Perlas et al. for example described a 40% failure for popliteal block [1]. We would suggest that on balance, it is neither necessary nor desirable to persist in attempts to establish the superiority of one technique over the other and would rather encourage the view that there are advantages as well as limitations pertaining to both. Consideration therefore should be given to a practice which is based on how both PNS and US approaches might be complementary rather than choosing one to the exclusion of the other. We submit that the algorithm we describe is a practical way to combine the two approaches and should result in a more favourable risk-benefit ratio for nerve localization. In a series of steps as illustrated in the algorithm, the first (and essential) is to obtain adequate training in both techniques [2]. In accordance with best practice, the procedure is performed on an awake or lightly sedated patient in order to maintain continuous verbal contact [3]. A sterile technique is mandatory. An initial ultrasound scan of the target anatomical area must be undertaken [4]. The scanning should be systematic and should cover a large area in order to accurately identify the anatomical components, particularly the neurovascular structures. The initial aim is to plan the needle trajectory and develop a strategy to optimise performance of the block. Whether an in-plane or out-of-plane technique is used it is essential that the full extent of the needle be visualized. Meanwhile the nerve stimulator should be set at 1 mA current intensity and 0.1 ms for the impulse duration. Nerve stimulation has a high specificity and low sensitivity [5] and it should always be kept in mind that in case of needle to nerve contact, it is still possible to increase current intensity without eliciting a motor or sensory response. During the procedure the needle tip position can be confirmed by hydrolocalization. This consists of repetitive injections of a small volume (usually less than 1 ml) of either the local anaesthetic itself, saline or dextrose 5% water (D5W). We recommend the use of D5W or saline as safer during needle positioning, when the needle tip may contact the nerve(s). Gentili et al. has shown in an experimental study that no neural damage occurred after saline injection, even if it was administered intrafascicularly [6]. D5W is preferred as it is a nonionic solution and in contrast to saline it potentiates the electrical field for the nerve stimulator [7]. Priority should be given to US, when the quality of the image is good and the anatomical structures can be easily identified. A tangential rather than a direct approach will provide optimal spread of the local anaesthetic and should therefore be chosen. In the tangential approach, when the needle is positioned slightly beyond the nerve (in order to obtain a circumferential spread of local anaesthetic) the minimum current intensity will be inevitably increased. If the quality of the image is poor, nerve stimulation assumes greater importance. In both cases, finding the minimum stimulating current intensity is essential [3] as it indicates the distance between the needle tip and the nerve (more precisely, the nearest nerve fascicle) as well as providing functional information. Strict adherence to safe practice should be maintained [3] and as with any regional technique it is essential to aspirate before injecting the solution and be aware that US images may give a false sense of security. Manoeuvres of the probe such as applying and then releasing pressure on the tissues can localise venous structures and define the relationship of the needle to the vein. While the width of the US beam is in the order of 1mm, it is essential to position the US field exactly over the needle tip to allow visualization of the first millilitre of hypoechoic fluid injected [4]. Nerve stimulators, e.g. Stimuplex HNS 12 (B Braun), that display the electrical impedance on their screen provide valuable information and should be used [8]. At a constant stimulating current intensity, any modification of the electrical impedance observed may be indicative of pre-injection intraneural needle placement. Absence of variation or a mild increase in electrical impedance during the injection of a few millilitres of D5W indicates intravascular needle position [9]. Extrafascicular injection should be of low resistance and painless. Whether needle repositioning is required depends on the pattern of fluid spread seen on the US image. An optimal spread, in contact with and circumferential to the nerve will permit a reduced injection volume of local anaesthetic, provided that it is dispersed along the nerve. When this is not the case, the needle should be repositioned. The overall aim should be to inject the local anaesthetic at the correct site, to minimise the dose while administering an adequate volume of solution. Throughout the procedure the operator should continuously assess the advantages and limitations of both techniques to obtain the most favourable risk-benefit ratio for the patient. In our view, it is necessary to combine techniques using a rigorous procedure for the optimum result. The algorithm we propose may be simplified and individualized according to preference but it should be kept in mind that each step removed is a loss of potentially useful information. Authors Addresses: Jochum: Colmar France. Bouaziz,Bondar,Egan: Nancy France Delaunay: Annecy France References: 1. Abrahams MS, Aziz MF, Fu RF, Horn JL. Ultrasound guidance compared with electrical neurostimulation for peripheral nerve block: a systematic review and meta- analysis of randomized controlled trials. Br J Anaesth 2009;102:408-17. 2. Sites BD, Chan VW, Neal JM, Weller R, Grau T, Koscielniak-Nielsen ZJ, Ivani G. The American Society of Regional Anesthesia and Pain Medicine and the European Society of Regional Anaesthesia and Pain Therapy Joint Committee Recommendations for Education and Training in Ultrasound-Guided Regional Anesthesia. Reg Anesth Pain Med 2009;34:40- 46. 3. Les blocs périphériques des membres chez l’adulte. Recommandations pour la pratique clinique. RPC publiées par la SFAR. http://sfar.org/t/spip.php?article184 (Mis en ligne le 2 mars 2003). 4. Brull R, Perlas A, Cheng PH, Chan VW. Minimizing the risk of intravascular injection during ultrasound-guided peripheral nerve blockade [Letter]. Anesthesiology 2008;109:1142. 5. Perlas A, Niazi A, McCartney C, Chan V, Xu D, Abbas S. The sensitivity of motor response to nerve stimulation and paresthesia for nerve localization as evaluated by ultrasound. Reg Anesth Pain Med 2006;31:445- 50. 6. Gentili F, Hudson A, Kline DG, Hunter D. Peripheral nerve injection injury: An experimental study. Neurosurgery 1979;4:244-53. 7. Tsui BC, Kropelin B, Ganapathy S, Finucane B. Dextrose 5% in water: fluid medium for maintening electrical stimulation of peripheral nerves during stimulating catheter placement. Acta Anaesthesiol Scand 2005;49:1562-5. 8. Jochum D, Iohom G, Diarra DP, Loughnane F, Dupré LJ, Bouaziz H. An objective assessment of nerve stimulators used for peripheral nerve blockade. Anaesthesia 2006;61:557- 64. 9. Tsui BCH, Chin JH. Electrical impedance to warn of intravascular needle placement. Reg Anesth Pain Med 2008;32:A-51. Conflict of Interest:None declared |
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Matthew S. Abrahams , Michael Aziz, Jean-LouisHorn
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We would like to thank Dr. Bouaziz et al for their interest in our paper, and for their comments regarding the combined use of peripheral nerve stimulation (PNS) and ultrasound (US) to perform peripheral nerve blocks. We mentioned in our discussion that any modality is going to have advantages and limitations, and it is important to consider these when deciding which technique or combination of techniques is best suited for a particular clinical scenario. We never meant to suggest that PNS lacks utility in the contemporary practice of Regional Anesthesia. We merely analyzed all of the available data from studies that had compared PNS to US. We were careful in our paper to avoid subjectivity, and our conclusions were based on our findings rather than any bias of our own. We agree that “one size does not fit all” but it is for that very reason we are opposed the proposed “algorithm” that Dr. Bouaziz et al describe. We maintain that every anesthesiologist who performs peripheral nerve blocks should perform them in the manner which they feel will be safest and most effective. For some, this will involve US only. Others will prefer to use PNS, while some may choose to use a combination of the two, or maybe even another modality such as paresthesia technique, fluoroscopy, or even CT guidance. The point is this: there is no one best approach that will work for every anesthesiologist for any block in any given patient. Within our group, there are many different practice styles, and we allow each attending anesthesiologist the freedom to decide what technique works best for them. In addition, Dr. Bouaziz et al do not actually propose an algorithmic approach for performing peripheral nerve blocks in their letter, they merely describe their technique. Their approach is very comprehensive and surely results in very high success rates. But it is by no means the only acceptable way to perform a nerve block. There are also some details of their technique that we do not support. For instance, we feel that initially setting the nerve stimulator at 1 mA could be uncomfortable for many patients, especially those with unstable fractures or other painful conditions. In addition, several studies (3, 4) have found that adding PNS to US guidance does not necessarily result in improved block success rates. This suggests that in many instances stimulation is unnecessary. In addition to lack of benefit, a combined approach is also potentially detrimental, as it can increase procedure time (and associated patient discomfort) and potentially increases the likelihood of mechanical trauma to the nerve from multiple needle passes if a motor response is not initially obtained despite needle/nerve contact. With regard to hydrolocalization, we recommend against using large volumes of D5W or saline as this can dilute the local anesthetic, potentially decreasing the “density” of a block (5) (especially important if the block is to be used for surgical anesthesia). We agree that use of US does not eliminate the potential for complications, and emphasize that all practitioners of regional anesthesia use established safety precautions regardless of modality used for nerve localization. The most important safety precaution will always be the presence of a knowledgeable, appropriately trained and experienced anesthesiologist during the performance of the block. Though he or she may choose to omit steps described by Dr. Bouaziz et al (or even to add additional steps), he or she will be the one who decides what information could be possibly useful and how to obtain it without exposing the patient to excessive risk or discomfort. Matthew Abrahams Michael Aziz Jean-Louis Horn References: 1. Abrahams MS, Aziz MF, Fu RF, Horn JL. Ultrasound guidance compared with electrical neurostimulation for peripheral nerve block: a systematic review and meta-analysis of randomized controlled trials. Br J Anaesth. 2009 Mar;102(3):408-17 2. Bouaziz et al. One size does not fit all: Proposal of an algorithm for the practice of ultrasonography in combination with nerve stimulation for peripheral nerve blockade. 3. Beach ML, Sites BD, Gallagher JD. Use of a nerve stimulator does not improve the efficacy of ultrasound-guided supraclavicular nerve blocks. J Clin Anesth. 2006 Dec;18(8):580-4 4. Chan VW, Perlas A, McCartney CJ, Brull R, Xu D, Abbas S. Ultrasound guidance improves success rate of axillary brachial plexus block. Can J Anaesth. 2007 Mar;54(3):176-82 5. Raymond SA. Subblocking concentrations of local anesthetics: effects on impulse generation and conduction in single myelinated sciatic nerve axons in frog. Anesth Analg. 1992 Dec;75(6):906-21. Conflict of Interest:None declared |
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Hervé Bouaziz , [Denis Jochum], [Attila Bondar], [Laurent Delaunay], [Michael Egan], [Hervé Bouaziz]
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Several articles have been published recently comparing the use of ultrasound (US) to that of peripheral stimulator (PNS) as nerve blocking techniques. We have read the meta-analysis by Abrahams et al. of randomized controlled trials, which suggests the greater efficacy of US compared to PNS [1]. Though there are many interesting points to the meta- analysis, Abrahams acknowledges in Appendix A of his review and in the subsequent correspondence, that of the 9 studies used, 3 used an inappropriate motor response as an endpoint and others opted for too high a minimal stimulating current [1]. These practices greatly reduced the effectiveness of nerve blocks using PNS. Perlas et al. for example described a 40% failure for popliteal block [1]. We would suggest that on balance, it is neither necessary nor desirable to persist in attempts to establish the superiority of one technique over the other and would rather encourage the view that there are advantages as well as limitations pertaining to both. Consideration therefore should be given to a practice which is based on how both PNS and US approaches might be complementary rather than choosing one to the exclusion of the other. We submit that the algorithm we describe is a practical way to combine the two approaches and should result in a more favourable risk-benefit ratio for nerve localization. In a series of steps as illustrated in the algorithm, the first (and essential) is to obtain adequate training in both techniques [2]. In accordance with best practice, the procedure is performed on an awake or lightly sedated patient in order to maintain continuous verbal contact [3]. A sterile technique is mandatory. An initial ultrasound scan of the target anatomical area must be undertaken [4]. The scanning should be systematic and should cover a large area in order to accurately identify the anatomical components, particularly the neurovascular structures. The initial aim is to plan the needle trajectory and develop a strategy to optimise performance of the block. Whether an in-plane or out-of-plane technique is used it is essential that the full extent of the needle be visualized. Meanwhile the nerve stimulator should be set at 1 mA current intensity and 0.1 ms for the impulse duration. Nerve stimulation has a high specificity and low sensitivity [5] and it should always be kept in mind that in case of needle to nerve contact, it is still possible to increase current intensity without eliciting a motor or sensory response. During the procedure the needle tip position can be confirmed by hydrolocalization. This consists of repetitive injections of a small volume (usually less than 1 ml) of either the local anaesthetic itself, saline or dextrose 5% water (D5W). We recommend the use of D5W or saline as safer during needle positioning, when the needle tip may contact the nerve(s). Gentili et al. has shown in an experimental study that no neural damage occurred after saline injection, even if it was administered intrafascicularly [6]. D5W is preferred as it is a nonionic solution and in contrast to saline it potentiates the electrical field for the nerve stimulator [7]. Priority should be given to US, when the quality of the image is good and the anatomical structures can be easily identified. A tangential rather than a direct approach will provide optimal spread of the local anaesthetic and should therefore be chosen. In the tangential approach, when the needle is positioned slightly beyond the nerve (in order to obtain a circumferential spread of local anaesthetic) the minimum current intensity will be inevitably increased. If the quality of the image is poor, nerve stimulation assumes greater importance. In both cases, finding the minimum stimulating current intensity is essential [3] as it indicates the distance between the needle tip and the nerve (more precisely, the nearest nerve fascicle) as well as providing functional information. Strict adherence to safe practice should be maintained [3] and as with any regional technique it is essential to aspirate before injecting the solution and be aware that US images may give a false sense of security. Manoeuvres of the probe such as applying and then releasing pressure on the tissues can localise venous structures and define the relationship of the needle to the vein. While the width of the US beam is in the order of 1mm, it is essential to position the US field exactly over the needle tip to allow visualization of the first millilitre of hypoechoic fluid injected [4]. Nerve stimulators, e.g. Stimuplex HNS 12 (B Braun), that display the electrical impedance on their screen provide valuable information and should be used [8]. At a constant stimulating current intensity, any modification of the electrical impedance observed may be indicative of pre-injection intraneural needle placement. Absence of variation or a mild increase in electrical impedance during the injection of a few millilitres of D5W indicates intravascular needle position [9]. Extrafascicular injection should be of low resistance and painless. Whether needle repositioning is required depends on the pattern of fluid spread seen on the US image. An optimal spread, in contact with and circumferential to the nerve will permit a reduced injection volume of local anaesthetic, provided that it is dispersed along the nerve. When this is not the case, the needle should be repositioned. The overall aim should be to inject the local anaesthetic at the correct site, to minimise the dose while administering an adequate volume of solution. Throughout the procedure the operator should continuously assess the advantages and limitations of both techniques to obtain the most favourable risk-benefit ratio for the patient. In our view, it is necessary to combine techniques using a rigorous procedure for the optimum result. The algorithm we propose may be simplified and individualized according to preference but it should be kept in mind that each step removed is a loss of potentially useful information. References: 1. Abrahams MS, Aziz MF, Fu RF, Horn JL. Ultrasound guidance compared with electrical neurostimulation for peripheral nerve block: a systematic review and meta- analysis of randomized controlled trials. Br J Anaesth 2009;102:408-17. 2. Sites BD, Chan VW, Neal JM, Weller R, Grau T, Koscielniak-Nielsen ZJ, Ivani G. The American Society of Regional Anesthesia and Pain Medicine and the European Society of Regional Anaesthesia and Pain Therapy Joint Committee Recommendations for Education and Training in Ultrasound-Guided Regional Anesthesia. Reg Anesth Pain Med 2009;34:40- 46. 3. Les blocs périphériques des membres chez l’adulte. Recommandations pour la pratique clinique. RPC publiées par la SFAR. http://sfar.org/t/spip.php?article184 (Mis en ligne le 2 mars 2003). 4. Brull R, Perlas A, Cheng PH, Chan VW. Minimizing the risk of intravascular injection during ultrasound-guided peripheral nerve blockade [Letter]. Anesthesiology 2008;109:1142. 5. Perlas A, Niazi A, McCartney C, Chan V, Xu D, Abbas S. The sensitivity of motor response to nerve stimulation and paresthesia for nerve localization as evaluated by ultrasound. Reg Anesth Pain Med 2006;31:445-50. 6. Gentili F, Hudson A, Kline DG, Hunter D. Peripheral nerve injection injury: An experimental study. Neurosurgery 1979;4:244-53. 7. Tsui BC, Kropelin B, Ganapathy S, Finucane B. Dextrose 5% in water: fluid medium for maintening electrical stimulation of peripheral nerves during stimulating catheter placement. Acta Anaesthesiol Scand 2005;49:1562-5. 8. Jochum D, Iohom G, Diarra DP, Loughnane F, Dupré LJ, Bouaziz H. An objective assessment of nerve stimulators used for peripheral nerve blockade. Anaesthesia 2006;61:557- 64. 9. Tsui BCH, Chin JH. Electrical impedance to warn of intravascular needle placement. Reg Anesth Pain Med 2008;32:A-51. *****(Authors request Algorithm to be attached here)**** Conflict of Interest:None declared |
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Colin Sinclair Department of Anaesthesia, Sunnybrook Health Sciences Centre, Toronto, ON, Canada, Colin J.L. McCartney
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We enjoyed the recent systematic review by Abrahams et al (1) demonstrating the advantages of ultrasound-guided peripheral nerve block but disagree with one of their conclusions. The authors state in their discussion that it is less clear if ultrasound (US) substantially improves outcomes for experienced anaesthetists yet in their results 11 out of 13 (85%) studies were performed by this group. We contend however that it is presently not clear whether trainees in anaesthesia or the non-expert occasional regional anaesthetist gain any advantage using ultrasound compared to more traditional techniques. At the present time it seems desirable to teach trainees to a level of competence in ultrasound-guided regional anaesthesia given the evidence of efficacy of these techniques. However it is not clear whether trainees themselves would prefer to be taught by ultrasound or traditional techniques, or both. We believe that they are not mutually exclusive techniques but are complementary. Ultrasound scanning may be used to assess for anatomical variants or to refine a landmark approach (2). We need more studies comparing block efficacy and complication rates with either technique in the hands of trainees and to evaluate the trainees’ learning experience thereof. There is reluctance amongst some to teach purely ultrasound-guided techniques because technology can break down; or competition for the machine can ensure that it is “unavailable”. We have been faced with both situations in our practice and an alternative approach was then invaluable. Educators are facing a hurdle, as the clinical practice of regional anesthesia over the last five years is undergoing transition from traditional nerve stimulation to ultrasound- guided techniques. This transition has perhaps diluted the experience that trainees receive in either technique. Such transition necessitates a change in our educational models, with an increasing need to develop teaching curricula to standardise the practice and teaching of regional anaesthesia (3). To date there is little consensus as to how much time should be allocated to teaching either technique but it is clear that we need further research to guide us in these decisions. References (1) Abrahams MS, Aziz MF, Fu RF, Horn JL. Ultrasound guidance compared with electrical neurostimulation for peripheral nerve block: a systematic review and meta-analysis of randomized controlled trials. British Journal of Anaesthesia 2009; 102: 408-17. (2) Hite BW, McCartney CJ. Pro/Con: teaching residents with ultrasound hinders postgraduate practice of regional anesthesia. ASRA News 2007; 6–8. (3) Marhofer P, Chan VW. Ultrasound-guided regional anesthesia: current concepts and future trends. Anesthesia and Analgesia 2007; 104: 1265-9 Conflict of Interest:Honararia for speaking engagement to Dr. McCartney: GE Medical |
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Andrew T Wilson
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Editor-- It is always a heart sink moment when the meta-analysis appears. It is then we realise that all the work put into our small, underpowered but well intentioned studies just hasn’t been enough to answer the question we desperately want to prove. Indeed every negative study tends to disprove the theory. Abrahams and colleagues should be congratulated on their honesty as to the limitations of their study and their guarded “suggestion” of an improvement in block success with Ultasound (US). The majority of the studies included were small and unsurprisingly didn’t reach significance. However the largest study of 160 patients for interscalene blocks by Kapral1 did reach significance with higher success in the US group. Many published studies on US quote significant results for secondary outcomes such as block onset time, patient satisfaction, number of needle stabs and minimum dose required and these tend to cloud the issue. We as practising anaesthetists really want to know differences in success rate and major complication rate. I think we all accept complications can still occur with US and whilst we are in our learning curve complication rates may even increase. If we look at published complication rates which for significant nerve damage are in their 1 in many thousands we cannot expect to show an improvement. It may well be intuitive that seeing a structure means you can more easily avoid it but proving it is a different matter and perhaps we should just accept that seeing is probably a benefit. Studies rightly therefore tend to concentrate on what may be provable and that is an improvement in success rate. Why then did this meta- analysis only “suggest” an improvement in success rates with US. The answer I believe lies in the heterogenicity of blocks. With interscalene US for instance it is significantly easier to see the hypoechogenic target nerves confined within a well demarcated fascial plane as beautifully demonstrated by Kapral and colleagues. In deed it is difficult to see why an US guided interscalene block could fail and yet the demonstration of a fascial band just above the upper trunk demonstrates very nicely why a “blind” block could fail. But the hyperechogenic sciatic nerve is much more difficult to visualise and differentiate from fat and muscle in the elderly population. It is not surprising therefore that a difference has not been demonstrated for this block. US is great for some procedures and less great for others. Perhaps we should see the publishing of a meta-analysis positively as a turning point in this field. Small studies will not demonstrate a difference and meta-analyses will only show a difference if they compare like with like. Let us stop trying to prove US’ value by showing it is superior to what is a tried and tested technique with a fairly high success rate. Unless we are going to do large well powered studies let’s just accept that it is probably better to see where you are putting the needle and more importantly for efficacy where we are putting the Local. I have tried in vain to find a study let alone a meta-analysis showing the laryngoscope has a higher success rate than blind intubation and yet we all accept it is better to see the target! A Wilson Leeds UK 1 Kapral S, Greher M, Huber G, et al. Ultrasonographic guidance improves the success rate of interscalene brachial plexus blockade. Reg Anesth Pain Med 2008;33:253-8 Conflict of Interest:None declared |
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Matthew S. Abrahams
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We would like to thank Dr. Aguirre for his interest in our meta- analysis and we would like to respond to his comments in order to clarify our findings and conclusions. Though Dr. Aguirre states that no trial has shown a statistical difference between ultrasound (US) and peripheral nerve stimulation (PNS) with regard to block success of safety, several of the studies that we have included for meta-analysis (1-3) did in fact show significant differences between the groups in terms of block success rates as well as adverse events (4 5). Also, the reviews and editorials that have been done to date (6 7) are subjective, and so the conclusions are merely based on the opinions of the authors rather than an actual formal analysis of the available data. We agree that onset of surgical anaesthesia, block success rates and need for conversion to general anaesthesia are indeed the most important parameters in clinical practice. We found that for all three of these parameters, US guidance was superior to PNS, and our results were highly statistically significant (p < 0.002 for all three). With regard to the system we developed to evaluate the studies’ methodologic quality, we were not satisfied with existing systems specifically because they did not assess whether or not the (to use the words of Dr. Aguirre) “respective state of the art” was employed for either study group. We weighted this aspect of each study more than any other aspect of study design other than the method of randomization because we felt it was essential to compare “apples to apples” and we have explicitly stated which studies were flawed due to potentially unfair comparisons due to sub-optimal use of either modality. This information is available as a supplement to the paper which is available on-line (Appendix A). In addition, the other aspects of study design that we included in our scoring system for methodologic quality have been used by other validated scoring systems (8) and are in accordance with the CONSORT statement (9), as failure to properly randomize patients or adhere to pre- defined inclusion criteria can significantly affect the results of randomized trials (10-12). Neither of the “validated” grading systems cited by Dr. Aguirre (13 14) take into account whether or not a “state of the art” technique has been used in either study arm (both focus on the so -called “secondary endpoints like randomization, inclusion criteria, etc.”), and as such he would likely dismiss either one as unsatisfactory. Despite Dr. Aguirre’s concerns over bias, both of the studies he cites as having good methodologic quality (those by Casati et al (15) and Macaire et al (16), and many of the other studies we included (1, 2, 5)) had patients in the PNS group who could not have blocks completed with PNS and were subsequently blocked using US or who were dropped from the study for other unexplained reasons. These patients were excluded from analysis, which favors the PNS groups as they were not recorded as block failures and the data were not analyzed on an intent-to-treat basis. This seems to us to be an important methodologic bias, though it may not bother Dr. Aguirre as it does not favor US. We have analyzed the data for evidence of publication bias, and found none. To the contrary, several of the studies we included were accompanied by editorials or letters (many by Dr. Aguirre) to temper enthusiasm for US guidance (17-22), and reports of complications associated with US-guided blocks have received a great deal of attention despite the lack of conclusive evidence that the block caused the complication (23-25). We agree with Dr. Aguirre that the minimum stimulating currents were probably too high in some of these studies, and we cited the same study by Neuburger et al (26) when we mentioned this in our discussion. We readily acknowledge that the studies to date that have compared US guidance to peripheral nerve stimulation (PNS) for peripheral nerve block procedures have not been perfect. For this reason, we tried to highlight their flaws in our discussion, and described them in greater detail in Appendix A. It is specifically because the most of the studies did not have sufficient power to achieve statistical significance that we undertook the meta-analysis. We agree that the design of the studies could have influenced the findings, and we specifically pointed out instances where we felt this could be the case (Appendix A). The study by Kapral et al (3) had two points subtracted from its quality score because they used (in our opinion) an inappropriate (27) (hand/forearm) motor response, and because a multiple-injection technique was frequently used in the US group, while the blocks in the PNS group were all single injections. We agree that interscalene blocks are not ideal for elbow surgery, though with a distal motor response as the endpoint, these blocks are essentially supraclavicular blocks, and as such are not wholly inappropriate, as a distal motor response for supraclavicular block has been shown to correlate with a high rate of block success for surgical procedures of the distal upper extremity (even with high minimum acceptable stimulating currents) and should produce local anesthetic spread around the middle and lower trunks of the brachial plexus (28 29). In fact, the block failures in the PNS arm of this study were predominantly for shoulder cases due to sparing of the C5 nerve root distribution. We also pointed out the low success rate in the study on popliteal block by Perlas et al (2), which we also attributed to the use of an inappropriate motor endpoint (dorsiflexion or eversion). Not surprisingly, most of the failed blocks in the PNS group did have one of these motor responses rather than plantar flexion, which has been shown to result in a higher block success rate (30). We pointed out this fact explicitly in Appendix A, and we subtracted two points from this study’s quality score for this reason. We also questioned the use of a triceps motor response as an endpoint for blockade of the radial nerve in the study by Chan et al (1) (see Appendix A) as more distal response has been shown to produce a higher block success rate (31). The time to perform the blocks listed in these studies generally does include the “time-consuming standard procedure” of performing a sonographic exam of the block site prior to needle insertion. In the US groups the time to perform the block was defined as the time from initial contact between probe and patient, and the completion of local anaesthetic injection. In the PNS groups the time to perform the procedure was generally defined as the time from needle insertion to the completion of local anaesthetic injection. The “time-consuming standard procedure” of palpating, measuring and marking landmarks to determine the site of initial needle insertion was not included. It is hard to imagine how this indicates a bias in favor of US. One of the studies we included (32) specifically compared the time required to obtain an ultrasonic image adequate for needle insertion to the time required to identify and mark surface anatomy for supraclavicular blocks. Though they found that US took less time, the difference did not achieve statistical significance. The use of US in the studies we included was also associated with fewer needle insertions and/or redirections (15), a higher success rate on first needle insertion (33), and less patient discomfort during the block procedure (34), though too few studies reported these outcomes for us to pool data for meta-analysis. Also, these studies did not include patients for whom the anatomic landmarks could be difficult to locate (eg morbidly obese patients). In our experience, the use of US can be very helpful to perform peripheral blocks in patients who otherwise might not be considered good candidates for regional anaesthesia. Though the studies that we have included in our meta-analysis may not be perfect, they are the only evidence we currently have to compare US to PNS. We have tried to make abundantly clear the shortcomings of these studies, and Dr. Aguirre is only re-stating many of the points we brought up in our discussion. We welcome Dr. Aguirre or anyone else to perform additional well-designed randomized controlled trials (RCT’s) comparing US to PNS or to analyze any set of data they feel appropriate, and then draw their own conclusions. Our analysis is not a speculation or a wish, but a careful and objective analysis of the existing literature on the subject. RCT’s and meta-analyses are currently accepted as the strongest types of evidence when developing evidence-based guidelines. Though expert opinion is valuable in the absence of data, it is not weighted as heavily. Despite the strong beliefs held by some practitioners of regional anesthesia, the evidence in favor of US continues to accumulate. We invite them to try US rather than discount it because of their own preconceived notions. After they have some experience with US they will have a truly informed opinion. Matthew S. Abrahams MD Michael F. Aziz MD Jean-Louis Horn MD References: 1) Chan VW, Perlas A, McCartney CJ, et al. Ultrasound guidance improves success rate of axillary brachial plexus block. Can J Anaesth. 2007 Mar;54(3):176-82 2) Perlas A, Brull R, Chan VW, et al. Ultrasound guidance improves the success of sciatic nerve block at the popliteal fossa. Reg Anesth Pain Med. 2008 May-Jun;33(3):259-65 3) Kapral S, Greher M, Huber G, et al. Ultrasonographic guidance improves the success rate of interscalene brachial plexus blockade. Reg Anesth Pain Med. 2008 May-Jun;33(3):253-8 4) Liu FC, Liou JT, Tsai YF, et al. Efficacy of ultrasound-guided axillary brachial plexus block: a comparative study with nerve stimulator- guided method. Chang Gung Med J. 2005 Jun;28(6):396-402 5) Sauter AR, Dodgson MS, Stubhaug A, et al. Electrical nerve stimulation or ultrasound guidance for lateral sagittal infraclavicular blocks: a randomized, controlled, observer-blinded, comparative study. Anesth Analg. 2008 Jun;106(6):1910-5 6) Delaunay L, Plantet F, Jochum D. Ultrasound and regional anaesthesia. Ann Fr Anesth Reanim. 2009 Feb;28(2):140-60 7) Liu SS, Ngeow JE, Yadeau JT. Ultrasound-guided regional anesthesia and analgesia: a qualitative systematic review. Reg Anesth Pain Med. 2009 Jan-Feb;34(1):47-59 8) Urwin SC, Parker MJ, Griffiths R. General versus regional anaesthesia for hip fracture surgery: a meta-analysis of randomized trials. Br J Anaesth. 2000 Apr;84(4):450-5 9) Moher D, Schulz KF, Altman D; CONSORT Group (Consolidated Standards of Reporting Trials). The CONSORT statement: revised recommendations for improving the quality of reports of parallel-group randomized trials. JAMA. 2001 Apr 18;285(15):1987-91 10) Schulz KF, Chalmers I, Hayes RJ, et al. Empirical evidence of bias. Dimensions of methodological quality associated with estimates of treatment effects in controlled trials. JAMA. 1995 Feb 1;273(5):408-12 11) Schulz KF, Cates W Jr. Influence of methodological quality on study conclusions. JAMA. 2001 Nov 28;286(20):2546-7 12) Wood L, Egger M, Gluud LL, et al. Empirical evidence of bias in treatment effect estimates in controlled trials with different interventions and outcomes: meta-epidemiological study. BMJ. 2008 Mar 15;336(7644):601-5 13) Jadad AR, Moore RA, Carroll D, et al. Assessing the quality of reports of randomized clinical trials: is blinding necessary? Control Clin Trials. 1996 Feb;17(1):1-12 14) Atkins D, Best D, Briss PA, et al; GRADE Working Group. Grading quality of evidence and strength of recommendations. BMJ. 2004 Jun 19;328(7454):1490 15) Casati A, Danelli G, Baciarello M, et al. A prospective, randomized comparison between ultrasound and nerve stimulation guidance for multiple injection axillary brachial plexus block. Anesthesiology. 2007 May;106(5):992-6 16) Macaire P, Singelyn F, Narchi P, et al. Ultrasound- or nerve stimulation-guided wrist blocks for carpal tunnel release: a randomized prospective comparative study. Reg Anesth Pain Med. 2008 Jul-Aug;33(4):363 -8 17) Salinas FV, Neal JM. A tale of two needle passes. Reg Anesth Pain Med. 2008 May-Jun;33(3):195-8 18) Aguirre J, Blumenthal S, Borgeat A. Ultrasound guidance and success rates of axillary brachial plexus block--I. Can J Anaesth. 2007 Jul;54(7):583 19) Aguirre J, Valentin Neudörfer C, Ekatodramis G, et al. Ultrasound guidance for sciatic nerve block at the popliteal fossa should be compared with the best motor response and the lowest current clinically used in neurostimulation technique. Reg Anesth Pain Med. 2009 Mar-Apr;34(2):182-3 20) Fredrickson MJ, Borgeat A, Aguirre J, et al. Ultrasound-guided interscalene block should be compared with the accepted standard for the neurostimulation technique. Reg Anesth Pain Med. 2009 Mar-Apr;34(2):180 21) Mannion S, Capdevila X. Ultrasound guidance and success rates of axillary brachial plexus block--II. Can J Anaesth. 2007 Jul;54(7):584 22) Lang SA. Ultrasound and the femoral three-in-one nerve block: weak methodology and inappropriate conclusions. Anesth Analg. 1998 May;86(5):1147-8 23) Koff MD, Cohen JA, McIntyre JJ, et al. Severe brachial plexopathy after an ultrasound-guided single-injection nerve block for total shoulder arthroplasty in a patient with multiple sclerosis. Anesthesiology. 2008 Feb;108(2):325-8 24) Hebl JR. Ultrasound-guided regional anesthesia and the prevention of neurologic injury: fact or fiction? Anesthesiology. 2008 Feb;108(2):186 -8 25) Hadzic A, Sala-Blanch X, Xu D. Ultrasound guidance may reduce but not eliminate complications of peripheral nerve blocks. Anesthesiology. 2008 Apr;108(4):557-8 26) Neuburger M, Rotzinger M, Kaiser H. Electric nerve stimulation in relation to impulse strength. A quantitative study of the distance of the electrode point to the nerve. Anaesthesist. 2001 Mar;50(3):181-6 27) Silverstein WB, Saiyed MU, Brown AR. Interscalene block with a nerve stimulator: a deltoid motor response is a satisfactory endpoint for successful block. Reg Anesth Pain Med. 2000 Jul-Aug;25(4):356-9 28) Franco CD, Domashevich V, Voronov G, et al. The supraclavicular block with a nerve stimulator: to decrease or not to decrease, that is the question. Anesth Analg. 2004 Apr;98(4):1167-71 29) Abrahams MS, Panzer O, Atchabahian A, et al. Case report: limitation of local anesthetic spread during ultrasound-guided interscalene block. Description of an anatomic variant with clinical correlation. Reg Anesth Pain Med. 2008 Jul-Aug;33(4):357-9 30) Pianezza A, Gilbert ML, Minville V, et al. A modified mid-femoral approach to the sciatic nerve block: a correlation between evoked motor response and sensory block. Anesth Analg. 2007 Aug;105(2):528-30 31) Sia S, Lepri A, Magherini M, et al. A comparison of proximal and distal radial nerve motor responses in axillary block using triple stimulation. Reg Anesth Pain Med. 2005 Sep-Oct;30(5):458-63 32) Williams SR, Chouinard P, Arcand G, et al. Ultrasound guidance speeds execution and improves the quality of supraclavicular block. Anesth Analg. 2003 Nov;97(5):1518-23 33) Domingo-Triadó V, Selfa S, Martínez F, et al. Ultrasound guidance for lateral midfemoral sciatic nerve block: a prospective, comparative, randomized study. Anesth Analg. 2007 May;104(5):1270-4 34) Marhofer P, Sitzwohl C, Greher M, et al. Ultrasound guidance for infraclavicular brachial plexus anaesthesia in children. Anaesthesia. 2004 Jul;59(7):642-6 Conflict of Interest:None declared |
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Jose Aguirre, Consultant Anaesthetist , Philipp Ruland, Georgios Ekatodramis, Alain Borgeat
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A questionable review will not change facts about neurostimulation compared to ultrasound technique for regional anesthesia! We read with great interest the review by Abrahams et al.1 We respectfully but profoundly question the methodology used and the drawn conclusions. Because of the outstanding interest in this topic, it is of utmost importance that the main weaknesses and numerous limitations of this review are highlighted to avoid further confusion and to prevent questionable conclusions concerning this controversial topic. First, recent reviews and editorials have already reported, that no study comparing ultrasound technique (US) to nerve stimulation technique (NS) has found a statistical difference in success rates and safety. Current sparse evidence suggest that the use of US for peripheral nerve blocks may hasten block performance and onset of block. However, the only relevant parameters in clinical practice are onset of surgical anaesthesia, success rate and need for conversion to general anesthesia. None of theses endpoints has been significantly affected.2-5 The reported improvement of efficacy by Abrahams et al1 remains a speculation which can be mainly attributed firstly, to the weaknesses in the review design and secondly, to the low quality of the included papers Second, even though validated score systems6, 7 are well established, the authors created their own system to rate the methodological quality of the studies. It is disappointing that this review made the same methodological mistakes than hardly all included studies. Instead of focusing on the important study methodological bias, the quality of the analysed investigations was assessed by secondary endpoints like randomisation, inclusion criteria, etc. A basic rule to properly compare the two techniques is that they must be performed according to the respective state of the art. For instance, NS requires first a standardized stimulation current. Apart from the studies by Casati et al and Macaire et al8, 9 all studies had a rather inaccurate definition of nerve stimulation setting like: ‘injection was performed at a current < 0.5mA’. Neuburger et al 10 have shown that thresholds down to 0.3mA at a pulse with of 100μs are required to achieve a success rate of 95% in patients without polyneuropathy. Moreover, Eifert et al11 demonstrated a correlation between stimulation threshold and axillary block success rate. The observed failure rate was 10.7% when the stimulation threshold was 0.6mA. With a stimulation amplitude of 0.4mA, no failure occurred. Therefore, the vague settings of the neurostimulator can explain many of the failures with NS. Third, the inappropriate use of NS-guided block cannot furnish valid results. The study by Kapral et al12 is among almost all cited articles in this review a good example of acceptance of a wrong motor response for a specific block. In this study a distal response involving the hand was accepted as endpoint for NS-guided interscalene block. This is unacceptable. Moreover, 25% of the patients had elbow surgery. This type of surgery needs an infraclavicular, not an interscalene block. To summarize: the wrong block for one specific surgery, the wrong motor response for a specific block lead inevitably to doubtful results. According to the Grade system7, this is a good example of a poor quality article and should be removed from any serious reviews or metanalysis. Fourth, complications and time to perform the block, some of the secondary endpoints of this review, are apparently closely linked together.12, 13 Letters to the Editor by different supporter of the US blamed the authors of the case reports for not performing a thorough systematic sonographic survey of the intended block side before needle insertion.13, 14 Interestingly, this time-consuming standard procedure is not mentioned in the studies comparing US to NS cited in the review.15 Fifth, some published results dealing with success rate are not only questionable, but worrisome. For example Perlas et al16 reported a success rate of 60.6% for the popliteal block, an unacceptable low success rate for a quite simple block.17 What would happen if a surgeon had a success rate of 60%? Sixth, a proper power analysis has been rarely performed.18-22 When a low success rate, not corresponding to the standard, has been chosen for the sample size calculation its validity becomes questionable. Unexperienced and inadequate neurostimulaton, inappropriate block for specific surgery, acceptance of inappropriate motor responses are major methodological bias. The addition of bias will, without any surprise, create artificial conditions in favour of the US technique. The ability of US guidance to avoid complications and improve clinical relevant success rate is an appealing assumption. Generation of such evidence is an ambitious task and may or may not ultimately affect acceptance and popularity of ultrasound. There are still no published data to show conclusive superiority of neurostimulation in terms of block success and safety, yet it has become the golden standard of regional anaesthesia practice today. The same analogy may extend to ultrasound. Obviously, a difference in block outcome cannot be demonstrated for ultrasound in experienced hands. Yet, popular preference and pressure made by US supporters associated with the irresistible wish to be trendy and supported by dubious studies lead to questionable conclusions that may ultimately launch ultrasound as the preferred technique. The almost religious belief that the ability to continuously monitor needle placement is a bulletproof technique to accomplish safe and successful regional anaesthesia remains nevertheless only speculation or a wish. A review should be based on evidence. Evidence is a real science, but science is neither speculation nor a wish. References 1. Abrahams MS, Aziz MF, Fu RF, Horn JL. Ultrasound guidance compared with electrical neurostimulation for peripheral nerve block: a systematic review and meta-analysis of randomized controlled trials. Br J Anaesth 2009; 102: 408-17 2. Delaunay L, Plantet F, Jochum D. [Ultrasound and regional anaesthesia.]. Ann Fr Anesth Reanim 2009 3. Liu SS, Wu CL. The effect of analgesic technique on postoperative patient-reported outcomes including analgesia: a systematic review. Anesth Analg 2007; 105: 789-808 4. Hebl JR. Ultrasound-guided regional anesthesia and the prevention of neurologic injury: fact or fiction? Anesthesiology 2008; 108: 186-8 5. Hadzic A, Sala-Blanch X, Xu D. Ultrasound guidance may reduce but not eliminate complications of peripheral nerve blocks. Anesthesiology 2008; 108: 557-8 6. Jadad AR, Moore RA, Carroll D, et al. Assessing the quality of reports of randomized clinical trials: is blinding necessary? Control Clin Trials 1996; 17: 1-12 7. Atkins D, Best D, Briss PA, et al. Grading quality of evidence and strength of recommendations. BMJ 2004; 328: 1490 8. Casati A, Danelli G, Baciarello M, et al. A prospective, randomized comparison between ultrasound and nerve stimulation guidance for multiple injection axillary brachial plexus block. Anesthesiology 2007; 106: 992-6 9. Macaire P, Singelyn F, Narchi P, Paqueron X. Ultrasound- or nerve stimulation-guided wrist blocks for carpal tunnel release: a randomized prospective comparative study. Reg Anesth Pain Med 2008; 33: 363-8 10. Neuburger M, Rotzinger M, Kaiser H. [Electric nerve stimulation in relation to impulse strength. A quantitative study of the distance of the electrode point to the nerve]. Anaesthesist 2001; 50: 181-6 11. Eifert B, Hahnel J, Kustermann J. [Axillary blockade of the brachial plexus. A prospective study of blockade success using electric nerve stimulation]. Anaesthesist 1994; 43: 780-5 12. Kapral S, Greher M, Huber G, et al. Ultrasonographic guidance improves the success rate of interscalene brachial plexus blockade. Reg Anesth Pain Med 2008; 33: 253-8 13. Shankar H. Ultrasound-guided peripheral nerve blocks and intravascular injection. Anesthesiology 2008; 109: 1142-3; author reply 4, 4-5 14. Brull R, Perlas A, Cheng PH, Chan VW. Minimizing the risk of intravascular injection during ultrasound-guided peripheral nerve blockade. Anesthesiology 2008; 109: 1142; author reply 4, 4-5 15. Chan VW, Perlas A, McCartney CJ, Brull R, Xu D, Abbas S. Ultrasound guidance improves success rate of axillary brachial plexus block. Can J Anaesth 2007; 54: 176-82 16. Perlas A, Brull R, Chan VW, McCartney CJ, Nuica A, Abbas S. Ultrasound guidance improves the success of sciatic nerve block at the popliteal fossa. Reg Anesth Pain Med 2008; 33: 259-65 17. Borgeat A, Blumenthal S, Karovic D, Delbos A, Vienne P. Clinical evaluation of a modified posterior anatomical approach to performing the popliteal block. Reg Anesth Pain Med 2004; 29: 290-6 18. Domingo-Triado V, Selfa S, Martinez F, et al. Ultrasound guidance for lateral midfemoral sciatic nerve block: a prospective, comparative, randomized study. Anesth Analg 2007; 104: 1270-4, tables of contents 19. Oberndorfer U, Marhofer P, Bosenberg A, et al. Ultrasonographic guidance for sciatic and femoral nerve blocks in children. Br J Anaesth 2007; 98: 797-801 20. Marhofer P, Schrogendorfer K, Koinig H, Kapral S, Weinstabl C, Mayer N. Ultrasonographic guidance improves sensory block and onset time of three-in-one blocks. Anesth Analg 1997; 85: 854-7 21. Marhofer P, Schrogendorfer K, Wallner T, Koinig H, Mayer N, Kapral S. Ultrasonographic guidance reduces the amount of local anesthetic for 3-in-1 blocks. Reg Anesth Pain Med 1998; 23: 584-8 22. Marhofer P, Sitzwohl C, Greher M, Kapral S. Ultrasound guidance for infraclavicular brachial plexus anaesthesia in children. Anaesthesia 2004; 59: 642-6 Conflict of Interest:None declared |
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