BACKGROUND: In this study we evaluated the minimum stimulating current associated with intraneura... more BACKGROUND: In this study we evaluated the minimum stimulating current associated with intraneural needle placement and sonographic appearance of intraneural injection. METHODS: We inserted a needle 2 cm inside 28 pig nerves (brachial plexus in vivo), recorded the minimum current to elicit a motor response, and injected dye (5 mL) under ultrasound (US) imaging. RESULTS: The minimum current to elicit a motor response was 0.43 mA (range: 0.12-1.8 mA). Nerve expansion was visualized by US in 24 of 28 nerves. Histology revealed penetration of the epineurium in these same 24 nerves. There was no evidence of dysplasia within the fascicle of any nerve. CONCLUSIONS: US may prove useful to detect intraneural injection, whereas a motor response above 0.5 mA may not exclude intraneural needle placement. The correlation between intraneural injection and neurological dysfunction remains unclear.
Current techniques of brachial plexus block are &... more Current techniques of brachial plexus block are "blind," and nerve localization can be frustrating and time consuming. Previous studies on ultrasound-assisted brachial plexus blocks are mostly performed with scanning probes of 10 MHz or less. The authors tested the usefulness of a state-of-the-art, high-resolution ultrasound probe (up to 12 MHz) in identifying the brachial plexus in five locations of the upper extremity and in guiding needle advancement to target before nerve stimulation. In this prospective observational study, 15 volunteers underwent brachial plexus examination using an L12-L5 MHz probe and a Philips-ATL 5000 ultrasound unit in the interscalene, supraclavicular, infraclavicular, axillary, and midhumeral regions. Thereafter, an insulated block needle was advanced under direct ultrasound guidance to target nerves before confirmation by electrical nerve stimulation in five volunteers in each of the interscalene, supraclavicular, and axillary regions. The quality of brachial plexus images, anatomic variations, and the technique of needle advancement for nerve localization were recorded. The brachial plexus components were successfully identified in the transverse view as round to oval hypoechoic structures with small internal punctuate echos in all regions examined except the infraclavicular area (visualized in 27% of the cases). The authors' technique of advancing the needle in-line with the ultrasound beam allowed moment-by-moment observation of the needle shaft and tip movement at the time of nerve localization. Hypoechoic structures were stimulated electrically and confirmed to be nerves. These preliminary data show that the high-resolution L12-L5 probe provides good quality brachial plexus ultrasound images in the superficial locations i.e., the interscalene, supraclavicular, axillary, and midhumeral regions. The needle technique described here for ultrasound-assisted nerve localization provides real-time guidance and is potentially valuable for brachial plexus blocks.
Background: Few studies have examined the use of ultrasound for sciatic nerve localization. The a... more Background: Few studies have examined the use of ultrasound for sciatic nerve localization. The authors evaluated the usefulness of low-frequency ultrasound in identifying the sciatic nerve at three locations in the lower extremity and in guiding needle advancement to target before nerve stimulation.
Studies were identified in a search of MEDLINE (between July 1966 and December 1999) and EMBASE (... more Studies were identified in a search of MEDLINE (between July 1966 and December 1999) and EMBASE (from 1980) by using the following MeSH terms: brachial plexus block or nerve block,
Background and Objective: Seeking paresthesia and obtaining a motor response to an electrical sti... more Background and Objective: Seeking paresthesia and obtaining a motor response to an electrical stimulus are the two most common methods of nerve localization for the performance of peripheral-nerve blocks. However, these two endpoints do not always correlate, and the actual sensitivity and specificity of either method remains unknown. The objective of this study is to determine the sensitivity of paresthesia and motor response to electrical nerve stimulation as tools for nerve localization when a 22-gauge insulated needle is used for the performance of axillary-nerve block.
Canadian Journal of Anaesthesia-journal Canadien D Anesthesie, 2007
Purpose The purpose of this study is to determine if real time ultrasound guidance improves the s... more Purpose The purpose of this study is to determine if real time ultrasound guidance improves the success rate of axillary brachial plexus blockade. Methods Patients undergoing elective hand surgery were randomly assigned to one of three groups. Axillary blocks were performed using three motor response endpoints in the nerve stimulator (NS) Group, real-time ultrasound guidance in the ultrasound (US) Group and combined ultrasound and nerve stimulation in the USNS Group. Following administration of a standardized solution containing 2% lidocaine with 1:200,000 epinephrine and 0.5% bupivacaine (total 42 mL), sensory and motor functions were assessed by a blinded observer every five minutes for 30 min. A successful block was defined as complete sensory loss in the median, radial and ulnar nerve distribution by 30 min. The need for local and general anesthesia supplementation and post-block adverse events were documented. Results One hundred and eighty-eight patients completed the study. Block success rate was higher in Groups US and USNS (82.8% and 80.7%) than Group NS (62.9%) (P = 0.01 and 0.03 respectively). Fewer patients in Groups US and USNS required supplemental nerve blocks and/or general anesthesia. Postoperatively, axillary bruising and pain were reported more frequently in Group NS. Conclusion This study demonstrates that ultrasound guidance, with or without concomitant nerve stimulation, significantly improves the success rate of axillary brachial plexus block. Objectif Le but de cette étude est de déterminer si l’échoguidage en temps réel améliore le taux de succès du bloc du plexus brachial par approche axillaire. Méthode Des patients devant subir une chirurgie élective de la main ont été randomisés en trois groupes. Des blocs axillaires ont été effectués en utilisant: trois points de réponses motrices dans le groupe neurostimulateur (NS), l’échoguidage en temps réel dans le groupe échographie (EG), et l’échographie combinée à la stimulation nerveuse dans le troisième groupe (EGNS). Suite à l’administration d’une solution standardisée contenant de la lidocaïne 2 % avec épinéphrine (1:200 000) et de la bupivacaïne 0,5 % (total 42 mL), les fonctions sensitives et motrices ont été évaluées par un observateur neutre toutes les cinq minutes pendant 30 min. Un bloc réussi a été défini comme la perte complète de sensation dans la distribution des nerfs médian, radial et cubital après 30 min. La nécessité d’une anesthésie locale et générale supplémentaire ainsi que les effets négatifs post-bloc ont été documentés. Résultat Chez les 188 patients qui ont terminé l’étude, le taux de succès du bloc a été plus élevé dans les groupes EG et EGNS (82,8 % et 80,7 %) que dans le groupe NS (62,9 %) (P) =0,01 et 0,03 respectivement). Un nombre moins élevé de patients des groupes EG et EGNS a nécessité des blocs nerveux supplémentaires et/ou une anesthésie générale. Après l’opération, les hématomes et douleurs axillaires ont été plus fréquemment observés dans le groupe NS. Conclusion Cette étude démontre que l’échoguidage, avec ou sans neurostimulation concomitante, améliore de façon significative le taux de succès du bloc du plexus brachial par approche axillaire.
To quantify the motor threshold current of a needle following elicitation of paresthesia during a... more To quantify the motor threshold current of a needle following elicitation of paresthesia during axillary brachial plexus block (ABPB). This is a prospective, observational study of ABPB in 72 patients. Having elicited paresthesia, the minimum current required to produce a motor response was noted. The development and success of the block were subsequently followed. Nineteen blocks were excluded (18 because of arterial puncture and 1 blocked needle). Of the remaining 53 blocks, 41 (77%) produced a motor response at 0.5 mA or less. The median current was 0.17 mA (range, 0.03 to 3.3 mA). The site of initial paresthesia and subsequent motor response were related in 43 (81%) of cases. A needle position causing paresthesia produced a motor response at 0.5 mA or less in 77% of cases studied. This current may, therefore, be a reasonable threshold to aim for when performing an ABPB.
The scope of ultrasound imaging guidance for regional anesthesia is growing rapidly. Preliminary ... more The scope of ultrasound imaging guidance for regional anesthesia is growing rapidly. Preliminary data, although limited, suggest that ultrasound can improve block success rate and decrease complications. In this review, we describe the basic principles of ultrasound scanning and needling techniques for nerve blocks, highlight some of the data on clinical outcome, discuss specific limitations of ultrasound for regional anesthesia, and speculate on the future direction for physician training and competency assessment with this technology.
BACKGROUND: In this study we evaluated the minimum stimulating current associated with intraneura... more BACKGROUND: In this study we evaluated the minimum stimulating current associated with intraneural needle placement and sonographic appearance of intraneural injection. METHODS: We inserted a needle 2 cm inside 28 pig nerves (brachial plexus in vivo), recorded the minimum current to elicit a motor response, and injected dye (5 mL) under ultrasound (US) imaging. RESULTS: The minimum current to elicit a motor response was 0.43 mA (range: 0.12-1.8 mA). Nerve expansion was visualized by US in 24 of 28 nerves. Histology revealed penetration of the epineurium in these same 24 nerves. There was no evidence of dysplasia within the fascicle of any nerve. CONCLUSIONS: US may prove useful to detect intraneural injection, whereas a motor response above 0.5 mA may not exclude intraneural needle placement. The correlation between intraneural injection and neurological dysfunction remains unclear.
Current techniques of brachial plexus block are &... more Current techniques of brachial plexus block are "blind," and nerve localization can be frustrating and time consuming. Previous studies on ultrasound-assisted brachial plexus blocks are mostly performed with scanning probes of 10 MHz or less. The authors tested the usefulness of a state-of-the-art, high-resolution ultrasound probe (up to 12 MHz) in identifying the brachial plexus in five locations of the upper extremity and in guiding needle advancement to target before nerve stimulation. In this prospective observational study, 15 volunteers underwent brachial plexus examination using an L12-L5 MHz probe and a Philips-ATL 5000 ultrasound unit in the interscalene, supraclavicular, infraclavicular, axillary, and midhumeral regions. Thereafter, an insulated block needle was advanced under direct ultrasound guidance to target nerves before confirmation by electrical nerve stimulation in five volunteers in each of the interscalene, supraclavicular, and axillary regions. The quality of brachial plexus images, anatomic variations, and the technique of needle advancement for nerve localization were recorded. The brachial plexus components were successfully identified in the transverse view as round to oval hypoechoic structures with small internal punctuate echos in all regions examined except the infraclavicular area (visualized in 27% of the cases). The authors' technique of advancing the needle in-line with the ultrasound beam allowed moment-by-moment observation of the needle shaft and tip movement at the time of nerve localization. Hypoechoic structures were stimulated electrically and confirmed to be nerves. These preliminary data show that the high-resolution L12-L5 probe provides good quality brachial plexus ultrasound images in the superficial locations i.e., the interscalene, supraclavicular, axillary, and midhumeral regions. The needle technique described here for ultrasound-assisted nerve localization provides real-time guidance and is potentially valuable for brachial plexus blocks.
Background: Few studies have examined the use of ultrasound for sciatic nerve localization. The a... more Background: Few studies have examined the use of ultrasound for sciatic nerve localization. The authors evaluated the usefulness of low-frequency ultrasound in identifying the sciatic nerve at three locations in the lower extremity and in guiding needle advancement to target before nerve stimulation.
Studies were identified in a search of MEDLINE (between July 1966 and December 1999) and EMBASE (... more Studies were identified in a search of MEDLINE (between July 1966 and December 1999) and EMBASE (from 1980) by using the following MeSH terms: brachial plexus block or nerve block,
Background and Objective: Seeking paresthesia and obtaining a motor response to an electrical sti... more Background and Objective: Seeking paresthesia and obtaining a motor response to an electrical stimulus are the two most common methods of nerve localization for the performance of peripheral-nerve blocks. However, these two endpoints do not always correlate, and the actual sensitivity and specificity of either method remains unknown. The objective of this study is to determine the sensitivity of paresthesia and motor response to electrical nerve stimulation as tools for nerve localization when a 22-gauge insulated needle is used for the performance of axillary-nerve block.
Canadian Journal of Anaesthesia-journal Canadien D Anesthesie, 2007
Purpose The purpose of this study is to determine if real time ultrasound guidance improves the s... more Purpose The purpose of this study is to determine if real time ultrasound guidance improves the success rate of axillary brachial plexus blockade. Methods Patients undergoing elective hand surgery were randomly assigned to one of three groups. Axillary blocks were performed using three motor response endpoints in the nerve stimulator (NS) Group, real-time ultrasound guidance in the ultrasound (US) Group and combined ultrasound and nerve stimulation in the USNS Group. Following administration of a standardized solution containing 2% lidocaine with 1:200,000 epinephrine and 0.5% bupivacaine (total 42 mL), sensory and motor functions were assessed by a blinded observer every five minutes for 30 min. A successful block was defined as complete sensory loss in the median, radial and ulnar nerve distribution by 30 min. The need for local and general anesthesia supplementation and post-block adverse events were documented. Results One hundred and eighty-eight patients completed the study. Block success rate was higher in Groups US and USNS (82.8% and 80.7%) than Group NS (62.9%) (P = 0.01 and 0.03 respectively). Fewer patients in Groups US and USNS required supplemental nerve blocks and/or general anesthesia. Postoperatively, axillary bruising and pain were reported more frequently in Group NS. Conclusion This study demonstrates that ultrasound guidance, with or without concomitant nerve stimulation, significantly improves the success rate of axillary brachial plexus block. Objectif Le but de cette étude est de déterminer si l’échoguidage en temps réel améliore le taux de succès du bloc du plexus brachial par approche axillaire. Méthode Des patients devant subir une chirurgie élective de la main ont été randomisés en trois groupes. Des blocs axillaires ont été effectués en utilisant: trois points de réponses motrices dans le groupe neurostimulateur (NS), l’échoguidage en temps réel dans le groupe échographie (EG), et l’échographie combinée à la stimulation nerveuse dans le troisième groupe (EGNS). Suite à l’administration d’une solution standardisée contenant de la lidocaïne 2 % avec épinéphrine (1:200 000) et de la bupivacaïne 0,5 % (total 42 mL), les fonctions sensitives et motrices ont été évaluées par un observateur neutre toutes les cinq minutes pendant 30 min. Un bloc réussi a été défini comme la perte complète de sensation dans la distribution des nerfs médian, radial et cubital après 30 min. La nécessité d’une anesthésie locale et générale supplémentaire ainsi que les effets négatifs post-bloc ont été documentés. Résultat Chez les 188 patients qui ont terminé l’étude, le taux de succès du bloc a été plus élevé dans les groupes EG et EGNS (82,8 % et 80,7 %) que dans le groupe NS (62,9 %) (P) =0,01 et 0,03 respectivement). Un nombre moins élevé de patients des groupes EG et EGNS a nécessité des blocs nerveux supplémentaires et/ou une anesthésie générale. Après l’opération, les hématomes et douleurs axillaires ont été plus fréquemment observés dans le groupe NS. Conclusion Cette étude démontre que l’échoguidage, avec ou sans neurostimulation concomitante, améliore de façon significative le taux de succès du bloc du plexus brachial par approche axillaire.
To quantify the motor threshold current of a needle following elicitation of paresthesia during a... more To quantify the motor threshold current of a needle following elicitation of paresthesia during axillary brachial plexus block (ABPB). This is a prospective, observational study of ABPB in 72 patients. Having elicited paresthesia, the minimum current required to produce a motor response was noted. The development and success of the block were subsequently followed. Nineteen blocks were excluded (18 because of arterial puncture and 1 blocked needle). Of the remaining 53 blocks, 41 (77%) produced a motor response at 0.5 mA or less. The median current was 0.17 mA (range, 0.03 to 3.3 mA). The site of initial paresthesia and subsequent motor response were related in 43 (81%) of cases. A needle position causing paresthesia produced a motor response at 0.5 mA or less in 77% of cases studied. This current may, therefore, be a reasonable threshold to aim for when performing an ABPB.
The scope of ultrasound imaging guidance for regional anesthesia is growing rapidly. Preliminary ... more The scope of ultrasound imaging guidance for regional anesthesia is growing rapidly. Preliminary data, although limited, suggest that ultrasound can improve block success rate and decrease complications. In this review, we describe the basic principles of ultrasound scanning and needling techniques for nerve blocks, highlight some of the data on clinical outcome, discuss specific limitations of ultrasound for regional anesthesia, and speculate on the future direction for physician training and competency assessment with this technology.
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Papers by Vincent Chan