- Email: [email protected]
Minimum volume of local anaesthetic required for an axillary brachial plexus block
British Journal of Anaesthesia 105 (3): 382–9 (2010)
CORRESPONDENCE Minimum volume of local anaesthetic required for an axillary brachial plexus block Editor—The minimum volume of local anaesthetic required for regional blocks has been the focus of several recent publications, and we read with interest the pilot study by Harper and colleagues.1 We were, however, surprised by the high failure rate of the blocks considering each branch of the axillary brachial plexus was surrounded by a ‘halo’ of local anaesthetic. Seven out of 19 patients required local anaesthetic infiltration by the surgeon and two required i.v. fentanyl. The mean onset times for complete sensory block were also surprisingly long, suggesting that it may have been the local anaesthetic’s proximity to the nerve that was the limiting factor rather than its volume. O’Donnell and Iohom2 showed that it was possible to achieve a 0% failure rate with rapid onset times using just 1 ml of local anaesthetic to surround each branch of the axillary brachial plexus. These markedly different results are unlikely to be entirely attributable to the higher concentration of lidocaine that was used (2% vs 1.5%). Another area of the study by Harper and colleagues that we found out of line with our own experience is the heavy sedation used before starting the block. All of the patients in the study received midazolam 0.15–0.25 mg kg21 and fentanyl 50 –100 mg i.v. For a 70 kg patient, this would equate to between 10.5 and 17.5 mg of midazolam. We do not think that any valid conclusions can therefore be deduced from this study as the data they present are inconsistent with other studies published and our own experience with these blocks. Technical issues with the performance of the blocks may be the key determinant of outcome in this study rather than the volumes of local anaesthetic investigated. D. R. Farquhar-Thomson * A. K. Baker Dorchester, UK * E-mail: [email protected] Editor—We read with great interest the article by Dr Harper and colleagues1 examining the minimum volume required to surround the constituent nerves of axillary brachial plexus and importantly whether this will provide an adequate nerve block. There are certain issues worthy of comment in this paper. First, regarding block success rate. Regional anaesthetists aim for a success rate in the order of 95% for axillary blocks, but in the study, the authors needed to supplement nine out of a total of 19 patients giving them an overall success rate of just 52.3%, despite indicating that anaesthesia was sufficient in the majority of patients.
Secondly, high failure rate after an apparent ‘adequate’ block is indicative of failure of the block assessment technique. In this study, the authors have used a three-point scale with a score of 3 being loss of discrimination to cold sensation. This may not have adequately predicted surgical anaesthesia. Recording the density of motor blockade would have been a useful addition to objectively assess the block density, which, although mentioned in the study methods as a secondary outcome measure, is not reported in the results. Thirdly, it would be valuable to know the details of the surgical procedure and whether they involved superficial structures or deeper bony interventions. For example, cutaneous analgesia in the distribution of the radial nerve will not necessarily allow manipulation of a painful Colles fracture. It is also obviously crucial from an anaesthetic perspective to know the dermatomal area involved, as forearm procedures will usually also require anaesthesia in the distribution of the medial cutaneous nerve of forearm and possibly of the median cutaneous nerve of arm as well, for comfortable tourniquet application. These cutaneous nerves could possibly be spared when using very low volumes for axillary block. Finally, it appears that significant amounts of premedication have been used for patients before block performance. In addition to fentanyl, midazolam is quoted at a dose of 0.15 –0.25 mg kg21 body weight, which for an average 70 kg individual represents a dose of 10.5 –17.5 mg, a considerable amount for anxiolysis or sedation. Is this erroneous by a factor of 10? Similarly, the block is said to have been performed ‘in the long axis of the nerve’, which is probably indicative of an in-plane approach by the author, but it conveys the impression that the needle is in-plane to the nerve as opposed to the probe. We all agree that most anaesthetists have used supramaximal doses of local anaesthetics to ensure block success. Reducing this volume with ultrasound and thus improving safety and reducing side-effects is a real possibility for some but not all blocks. However, before reducing the dose close to that mentioned by the authors, we need a much more robust block assessment technique to give a truly objective representation of ‘block success’ and avoid the risk of having to deal with more inadequate blocks. A. R. Satapathy* D. Coventry Dundee, UK * E-mail: [email protected] Editor—We thank Drs Farquhar-Thomson and Baker, and Drs Satapathy and Coventry for their interest in our work and welcome their comments.
& The Author [2010]. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved. For Permissions, please email: [email protected]
BJA
Correspondence
First, in response to the question of sedation, both authors draw attention to the excessive doses of midazolam apparently used. As suggested by Dr Satapathy, this indeed was a transcription error, where the quoted dose was erroneous by a factor of 10. This should have read 0.015 – 0.025 mg kg21. In fact, no patient received more than 2.5 mg of midazolam during the conduct of this study. We apologize for not spotting this error and thank both authors for highlighting this. In response to the specific questions posed by Dr Satapathy, patients achieved only a partial motor block on most occasions before the commencement of surgery. The exception was the musculocutaneous nerve which usually had a complete motor block within 10 min. We found that the volumes of local anaesthetic used in the study did not give a reliable motor block. The 19 patients in our study were scheduled to have plastic surgery or orthopaedic procedures such as tendon repairs or K wires of hand fractures. There were no major fracture manipulations or fixations. Both authors point out that, in this study, there was an unacceptably high failure rate. Most clinicians would agree that a regional anaesthetic technique that required some form of supplementation in almost 50% of cases is not clinically viable. It is important to re-emphasize, however, that this was a purely observational study. The advent of ultrasound-guided regional anaesthesia has led to very specific questions—‘now that we can see the local anaesthetic being injected around individual nerve fibres, how much should be injected?’ Is the minimum volume sufficient to produce surgical anaesthesia, and, if not, how much more needs to be injected? At the time of writing, the optimum dose of lidocaine 1.5%, required to produce effective anaesthesia in the individual branches of the axillary brachial plexus, is unknown. This study showed that the minimum volume of lidocaine 1.5% required to surround the nerves was insufficient to reliably produce adequate surgical anaesthesia within a 20 min period, hence the high supplementation rate. The challenge now is to find the optimum volume. Drs Farquhar-Thomson and Baker correctly state that O’Donnell and colleagues2 were able to produce reliable surgical anaesthesia with only lidocaine 2% (1 ml) to each of the branches of the brachial plexus. They state that the differences in volumes between ours and their work ‘are unlikely to be entirely attributable to the higher concentration of lidocaine’. We would disagree with him on this point. The reality is that, at present, the influence of drug concentration, volume, and total dose, when dealing with such small volumes, is unknown, so neither Dr Farquhar-Thomson nor anybody else, at present, can say for sure exactly how much influence a 33.3% difference in concentration has on clinical outcomes. While we may not have achieved the small volumes of O’Donnell and colleagues, we re-emphasize that our endpoint was determined as seeing the nerve surrounded by local anaesthetic, that is, a correctly performed block. If our target was not the nerve in question, no block would have been achieved with such small volumes. The difference in volumes required to surround the radial nerve, relatively
difficult to access, compared with the musculocutaneous nerve, relatively easy to access, reflect the challenge in ensuring that injected anaesthetic spreads as desired when the needle is positioned beside the nerve. Once again, we thank the authors for their interest in our work and welcome any further constructive comments.
Conflict of interest None declared. G. K. Harper M. A. Stafford * D. A. Hill Belfast, UK * E-mail: [email protected] 1 Harper GK, Stafford MA, Hill DA. Minimum volume of local anaesthetic required to surround each of the constituent nerves of the axillary brachial plexus, using ultrasound guidance: a pilot study. Br J Anaesth 2010; 104: 633– 6 2 O’Donnell BD, Iohom G. An estimation of the minimum effective anaesthetic volume of 2% lidocaine in ultrasound-guided axillary brachial plexus block. Anesthesiology 2009; 111: 25 –9
doi:10.1093/bja/aeq220
Comparison between single-step and balloon dilatational tracheostomy Editor—In addition to the conclusions of the randomized controlled trial comparing the use of the Ciaglia Blue Rhino tracheostomy device and the Ciaglia Blue Dolphin (CBD) tracheostomy device,1 my own limited trial of the Dolphin technique, when compared with the Rhino technique, led me to the following observations: (i) maintaining balloon position during inflation requires two pairs of hands, whereas the Rhino requires only one. (ii) Ventilation can easily be maintained with the Rhino dilator in situ, whereas the Dolphin balloon causes complete occlusion of the trachea. (iii) Bronchoscopic visualization of the tracheostomy from above after dilation revealed significantly greater tracheal injury after the balloon inflation when compared with the Rhino. I felt that this was the result of a complete lack of feedback with the balloon, which exerts a much greater radial force and delivers it at a greater speed. The Rhino, in comparison, gives feedback by way of resistance to insertion that permits the operator to modify their technique accordingly. Like the authors, I strongly endorse bronchoscopic guidance and visualization both during and after percutaneous tracheostomy. J. Ball * London, UK * E-mail: [email protected] Editor—We read with interest the randomized controlled trial comparing the use of the Ciaglia Blue Rhino tracheostomy
383
CORRESPONDENCE Minimum volume of local anaesthetic required for an axillary brachial plexus block Editor—The minimum volume of local anaesthetic required for regional blocks has been the focus of several recent publications, and we read with interest the pilot study by Harper and colleagues.1 We were, however, surprised by the high failure rate of the blocks considering each branch of the axillary brachial plexus was surrounded by a ‘halo’ of local anaesthetic. Seven out of 19 patients required local anaesthetic infiltration by the surgeon and two required i.v. fentanyl. The mean onset times for complete sensory block were also surprisingly long, suggesting that it may have been the local anaesthetic’s proximity to the nerve that was the limiting factor rather than its volume. O’Donnell and Iohom2 showed that it was possible to achieve a 0% failure rate with rapid onset times using just 1 ml of local anaesthetic to surround each branch of the axillary brachial plexus. These markedly different results are unlikely to be entirely attributable to the higher concentration of lidocaine that was used (2% vs 1.5%). Another area of the study by Harper and colleagues that we found out of line with our own experience is the heavy sedation used before starting the block. All of the patients in the study received midazolam 0.15–0.25 mg kg21 and fentanyl 50 –100 mg i.v. For a 70 kg patient, this would equate to between 10.5 and 17.5 mg of midazolam. We do not think that any valid conclusions can therefore be deduced from this study as the data they present are inconsistent with other studies published and our own experience with these blocks. Technical issues with the performance of the blocks may be the key determinant of outcome in this study rather than the volumes of local anaesthetic investigated. D. R. Farquhar-Thomson * A. K. Baker Dorchester, UK * E-mail: [email protected] Editor—We read with great interest the article by Dr Harper and colleagues1 examining the minimum volume required to surround the constituent nerves of axillary brachial plexus and importantly whether this will provide an adequate nerve block. There are certain issues worthy of comment in this paper. First, regarding block success rate. Regional anaesthetists aim for a success rate in the order of 95% for axillary blocks, but in the study, the authors needed to supplement nine out of a total of 19 patients giving them an overall success rate of just 52.3%, despite indicating that anaesthesia was sufficient in the majority of patients.
Secondly, high failure rate after an apparent ‘adequate’ block is indicative of failure of the block assessment technique. In this study, the authors have used a three-point scale with a score of 3 being loss of discrimination to cold sensation. This may not have adequately predicted surgical anaesthesia. Recording the density of motor blockade would have been a useful addition to objectively assess the block density, which, although mentioned in the study methods as a secondary outcome measure, is not reported in the results. Thirdly, it would be valuable to know the details of the surgical procedure and whether they involved superficial structures or deeper bony interventions. For example, cutaneous analgesia in the distribution of the radial nerve will not necessarily allow manipulation of a painful Colles fracture. It is also obviously crucial from an anaesthetic perspective to know the dermatomal area involved, as forearm procedures will usually also require anaesthesia in the distribution of the medial cutaneous nerve of forearm and possibly of the median cutaneous nerve of arm as well, for comfortable tourniquet application. These cutaneous nerves could possibly be spared when using very low volumes for axillary block. Finally, it appears that significant amounts of premedication have been used for patients before block performance. In addition to fentanyl, midazolam is quoted at a dose of 0.15 –0.25 mg kg21 body weight, which for an average 70 kg individual represents a dose of 10.5 –17.5 mg, a considerable amount for anxiolysis or sedation. Is this erroneous by a factor of 10? Similarly, the block is said to have been performed ‘in the long axis of the nerve’, which is probably indicative of an in-plane approach by the author, but it conveys the impression that the needle is in-plane to the nerve as opposed to the probe. We all agree that most anaesthetists have used supramaximal doses of local anaesthetics to ensure block success. Reducing this volume with ultrasound and thus improving safety and reducing side-effects is a real possibility for some but not all blocks. However, before reducing the dose close to that mentioned by the authors, we need a much more robust block assessment technique to give a truly objective representation of ‘block success’ and avoid the risk of having to deal with more inadequate blocks. A. R. Satapathy* D. Coventry Dundee, UK * E-mail: [email protected] Editor—We thank Drs Farquhar-Thomson and Baker, and Drs Satapathy and Coventry for their interest in our work and welcome their comments.
& The Author [2010]. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved. For Permissions, please email: [email protected]
BJA
Correspondence
First, in response to the question of sedation, both authors draw attention to the excessive doses of midazolam apparently used. As suggested by Dr Satapathy, this indeed was a transcription error, where the quoted dose was erroneous by a factor of 10. This should have read 0.015 – 0.025 mg kg21. In fact, no patient received more than 2.5 mg of midazolam during the conduct of this study. We apologize for not spotting this error and thank both authors for highlighting this. In response to the specific questions posed by Dr Satapathy, patients achieved only a partial motor block on most occasions before the commencement of surgery. The exception was the musculocutaneous nerve which usually had a complete motor block within 10 min. We found that the volumes of local anaesthetic used in the study did not give a reliable motor block. The 19 patients in our study were scheduled to have plastic surgery or orthopaedic procedures such as tendon repairs or K wires of hand fractures. There were no major fracture manipulations or fixations. Both authors point out that, in this study, there was an unacceptably high failure rate. Most clinicians would agree that a regional anaesthetic technique that required some form of supplementation in almost 50% of cases is not clinically viable. It is important to re-emphasize, however, that this was a purely observational study. The advent of ultrasound-guided regional anaesthesia has led to very specific questions—‘now that we can see the local anaesthetic being injected around individual nerve fibres, how much should be injected?’ Is the minimum volume sufficient to produce surgical anaesthesia, and, if not, how much more needs to be injected? At the time of writing, the optimum dose of lidocaine 1.5%, required to produce effective anaesthesia in the individual branches of the axillary brachial plexus, is unknown. This study showed that the minimum volume of lidocaine 1.5% required to surround the nerves was insufficient to reliably produce adequate surgical anaesthesia within a 20 min period, hence the high supplementation rate. The challenge now is to find the optimum volume. Drs Farquhar-Thomson and Baker correctly state that O’Donnell and colleagues2 were able to produce reliable surgical anaesthesia with only lidocaine 2% (1 ml) to each of the branches of the brachial plexus. They state that the differences in volumes between ours and their work ‘are unlikely to be entirely attributable to the higher concentration of lidocaine’. We would disagree with him on this point. The reality is that, at present, the influence of drug concentration, volume, and total dose, when dealing with such small volumes, is unknown, so neither Dr Farquhar-Thomson nor anybody else, at present, can say for sure exactly how much influence a 33.3% difference in concentration has on clinical outcomes. While we may not have achieved the small volumes of O’Donnell and colleagues, we re-emphasize that our endpoint was determined as seeing the nerve surrounded by local anaesthetic, that is, a correctly performed block. If our target was not the nerve in question, no block would have been achieved with such small volumes. The difference in volumes required to surround the radial nerve, relatively
difficult to access, compared with the musculocutaneous nerve, relatively easy to access, reflect the challenge in ensuring that injected anaesthetic spreads as desired when the needle is positioned beside the nerve. Once again, we thank the authors for their interest in our work and welcome any further constructive comments.
Conflict of interest None declared. G. K. Harper M. A. Stafford * D. A. Hill Belfast, UK * E-mail: [email protected] 1 Harper GK, Stafford MA, Hill DA. Minimum volume of local anaesthetic required to surround each of the constituent nerves of the axillary brachial plexus, using ultrasound guidance: a pilot study. Br J Anaesth 2010; 104: 633– 6 2 O’Donnell BD, Iohom G. An estimation of the minimum effective anaesthetic volume of 2% lidocaine in ultrasound-guided axillary brachial plexus block. Anesthesiology 2009; 111: 25 –9
doi:10.1093/bja/aeq220
Comparison between single-step and balloon dilatational tracheostomy Editor—In addition to the conclusions of the randomized controlled trial comparing the use of the Ciaglia Blue Rhino tracheostomy device and the Ciaglia Blue Dolphin (CBD) tracheostomy device,1 my own limited trial of the Dolphin technique, when compared with the Rhino technique, led me to the following observations: (i) maintaining balloon position during inflation requires two pairs of hands, whereas the Rhino requires only one. (ii) Ventilation can easily be maintained with the Rhino dilator in situ, whereas the Dolphin balloon causes complete occlusion of the trachea. (iii) Bronchoscopic visualization of the tracheostomy from above after dilation revealed significantly greater tracheal injury after the balloon inflation when compared with the Rhino. I felt that this was the result of a complete lack of feedback with the balloon, which exerts a much greater radial force and delivers it at a greater speed. The Rhino, in comparison, gives feedback by way of resistance to insertion that permits the operator to modify their technique accordingly. Like the authors, I strongly endorse bronchoscopic guidance and visualization both during and after percutaneous tracheostomy. J. Ball * London, UK * E-mail: [email protected] Editor—We read with interest the randomized controlled trial comparing the use of the Ciaglia Blue Rhino tracheostomy
383