Ultrasound identification of nerve cords in the infraclavicular fossa: a clinical study

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1 O R I G I N A L A R T I C L E Ultrasound identification of nerve cords in the infraclavicular fossa: a clinical study A. DI FILIPPO 1, S. ORANDO 1, A. LUNA 1, L. GIANESELLO 2, A. BOCCACCINI 2, M. C. CAMPOLO 2, A. R. DE GAUDIO 1 1Section of Anesthesia, Department of Critical Care, University of Florence, Florence, Italy; 2 Unit of Anesthesia and Intensive Care, Department of Orthopedics, Careggi Teaching Hospital, Florence, Italy A B S T R A C T Background. This study aimed to analyze nerve trunk anatomy in the infraclavicular fossa and to correlate these data with the most common anthropometric parameters. Methods. A Mylab 30 Gold (Esaote) and the linear transducer LA523 (7.5 MHz frequency) were used. The probe was oriented according to a parasagittal plane, parallel to the lateral chest wall and immediately medial to the coracoid process underneath the clavicle. Measurements included the distance between the artery and the cutaneous surface (mm) and the apical corner of the ultrasound image (mm), the number of identified nervous cords and their position related to the axillary artery, and the position and number of axillary veins. Sex, age, height, weight, body mass index (BMI), biceps girth, and breast size were recorded. Statistical analysis included calculation of linear Pearson correlation coefficient and Student s t test. Results. Two hundred and two consecutive patients were enrolled. The position of the three cords was highly variable around the artery. In a small but significant percentage of patients (8.9%), the medial and the lateral cords were located together at the top of the artery. The visibility of the trunks and the distance between the upper part of the artery and the apical corner of the ultrasound image correlated with anthropometric characteristics. The vein position with respect to the artery and nerves was markedly variable. Conclusion. Sono-anatomic study of the infraclavicular region adds important data that is useful when conducting nerve blocks to improve safety and likelihood of success. (Minerva Anestesiol 2012;78:450-5) Key words: Anesthesia, local - Ultrasonography - Anatomy - Peripheral nerves. After great success of ultrasound guided nerve blocks in the last fifteen years, studies on this method have concentrated on technique improvement, execution time, local anesthetic administration, success rate, and complication frequency. 1 Infraclavicular block is performed in a critical area where the nearby structures include large vessels and the pleural apex, which can be injured during the puncture. 2, 3 For this reason, infraclavicular block is mostly used when the anesthetist has a view of the structures with Comment in p ultrasound imaging. 4-8 In fact, the ultrasound has the added advantage of making evident the anatomy of the region and facilitates the execution of the block. So this type of block, more than any other, has received more benefits from enforcement action by ultrasonography and has seen a growing popularity. 5, 7 Unfortunately, there are many anatomic variations of the infraclavicular region vessels that have already been described, such as a bifida axillary artery 9 and abnormalities of the superficial and deep axillary artery. 10, 11 Anatomic variation could cause an accidental puncture of vessel or 450 MINERVA ANESTESIOLOGICA April 2012

2 Ultrasound identification of nerve cords in the infraclavicular fossa: a clinical study DI FILIPPO a difficulty to find response in the blind nerve stimulation technique. Furthermore, it is noteworthy that the ability to recognize nerves and other structures by ultrasound depends on the anatomical knowledge of the cross section in contrast to the usual longitudinal view. For these reasons, we performed a sonographic anatomical study of the infraclavicular region. The purpose of the study was to examine the effectiveness of ultrasonography in analyzing the nerve cords position compared to arterial landmarks, their visibility, and their distance from the skin in the infraclavicular fossa, and to correlate data with the most common anthropometric parameters. Materials and methods The clinical protocol was approved by the institutional Ethics Committee of the Azienda Ospedaliero Universitaria Careggi, and the patients gave an informed consent to participate. A polifunctional ultrasound machine (Mylab 30 Gold, Esaote) and the linear transducer LA523 (7.5 MHz frequency) were used. After preoperative evaluation, informed consent to study participation was obtained. The probe was oriented according to a parasagittal plane, parallel to the lateral chest wall, immediately medial to the coracoid process underneath the clavicle. The patient, in a supine position, held the arm abducted on his side. The transducer position was modified with minimal adjustment in order to obtain a perfect orthogonal scansion of the axillary artery, which appeared circular, and was maintained at the center of the visualization field. The image, taken by the study corrisponding author, for each patient, was frozen and, on the video, the following parameters were collected: distance between the upper part of the artery and the cutaneous surface (mm) and the distance between the upper part of the artery and the apical corner of the ultrasound image (mm). Two experienced anesthesists (more than five years experience) independently assessed the number of identified nervous cords and their position related to the axillary artery. They assigned to the cord position a corresponding amplitude in degrees (0, 30, 60, 90,120, 150, 180, 210, 240, 270, 300, 330, 360 ). When the analysis of the two anesthesiologists agreed, the patient was enrolled in the study. Cords were identified by their ultrasonographic characteristics as slightly dotted hypoechoic/ hyperechoic structures, or with the distinctive honeycomb appearance. The position and number of axillary veins were also detected with the color Doppler instrument. The identification of cords with electrical stimulation has not been performed because one of the purpose of the study was to test the ability of Ultrasound to identify cords. The only exclusion criteria was the minor age. The following parameters were collected from each patient: sex, age, height, weight, Body Mass Index (BMI), biceps girth, and breast size. Different parameters were compared using the linear Pearson correlation coefficient. Where reported, averages were compared with Student s t test. Data are reported as mean ± standard deviation. The alpha level was set at P<0.01. A post-hoc analysis of the power of the study was calculated for each dependent variables examined (Statepages.org post-hoc power analysis accessed August 2011). Results Two hundred and two consecutive adult patients, within an observation period of an year (from January 1 to December 31, 2010), which would indicate the performance of infraclavicular block, were enrolled. Mean age was 50.2±17.8 years, mean weight was 72.2±14.9 kg, mean height was 1.70±0.1, and mean BMI was 25±4.6 kg/m 2. The average distance between the upper part of the artery and the cutaneous surface and between the upper part of the artery and the apical corner of the ultrasound image was 2.6±0.7 and 3.4±0.7 cm, respectively. The number of distinguishable cords was 3 in 72 patients, 2 in 76 patients, and 0 or 1 in 51 patients (36%, 38%, and 26%, respectively). The lateral cord was visible in 80% of patients, the medial in 69%, and the posterior in 55%. In Figure 1 (A and B) an ultrasound image of Vol No. 4 MINERVA ANESTESIOLOGICA 451

3 DI FILIPPO Ultrasound identification of nerve cords in the infraclavicular fossa: a clinical study Figure 1. Ultrasound image of the infraclavicular region. A: 33 year old woman, BMI 34 kg/m 2 ; B: 30 year old woman, BMI 18. In patients of the same sex with similar ages, the difference in BMI leads to a considerable difference in the visualization of neural structures. In large part this is due to the greater thickness of the subcutaneous tissue. the infraclavicular region is reproduced (A: 33 years old woman, BMI 34 kg/m 2 ; B: 30 year old woman, BMI 18 kg/m 2 ). In the figure is highlighted as the difference in BMI leads to a considerable difference in the visualization of neural structures. In large part this is due to the greater thickness of the subcutaneous tissue According to the number of the identified cords, a significant difference between anthropometric parameters was found among study patients: in the group with one visible cord, all anthropometric parameters were significantly greater with the exception of height and age (Table I). The mean position of different cords related to the artery was 77 for medial, 316 for lateral, and 179 for posterior. The position variability was the highest for the medial cord (±57 ) and lowest for the posterior and lateral cords (±18 and ±28, respectively). Eighteen patients had both the lateral and medial cords at the 0 position. Anthropometric parameters were not significantly different in these subgroups if compared to patients with the classical position; therefore this anatomical variant was not predictable from an anthropometric point of view. In 41 patients the axillary vein could not be detected (20%); 1 was found in 125 patients (62%), 2 in 33 patients (16%), and more than 2 in 3 patients (1%). The mean position of the vein was 142, with a high degree of variability (±88 ). The distance between the upper part of the artery and the apical corner of the ultrasound image is very useful because it corresponds to the Table I. Anthropometric parameters in respect to the number of cords visible. Cords n 0-1 (N.=51) 2 (N.=76) 3 (N.=72) P Weight (kg) 78.6± ± ±12 <0.01 Height (m) 1.68± ± ±0.1 NS BMI (kg/m 2 ) 27.8± ± ±3.4 <0.01 Biceps girth (cm) 32± ± ±3.6 <0.01 Breast size 3.9± ±1 3.4 ±0.9 <0.01 P value statistically significant between group 1 versus 2 and 1 versus MINERVA ANESTESIOLOGICA April 2012

4 Ultrasound identification of nerve cords in the infraclavicular fossa: a clinical study DI FILIPPO Table II. Anthropometric parameters and visible cords in the greater than 4 cm (N.=35 patients) and less than 4 cm (N.= 167 patients) subgroups. Corner-Artery distance <4 cm Corner-Artery distance >4 cm P Age (yrs) 50.4 ± ± 13.7 NS Weight (kg) ± ± 13.6 <0.01 Height (m) 1.69 ± ± 0.08 NS BMI (kg/m 2 ) 24 ± ± 5 <0.01 Biceps girth (cm) 28.4 ± ± 6 <0.01 Breast size 3.4 ±1 4.1 ±1.2 NS N of identified cords 2.2 ± ± 0.7 <0.01 minimal path that the needle must cross to reach the injection area. As expected, this distance correlated with BMI (R=0.65; P<0.01), weight (R=0.58; P<0.01), and biceps girth (R=0.59; P<0.01). If a distance greater than 4 cm is considered a critical length, in that lengths greater than this create operative difficulties with the 5 cm needle used in blocks, we can divide patients in 2 groups. The group with a corner-artery distance greater than 4 cm consisted of 35 patients (18%), mean age 48.9±13.7, and the group with a distance less than 4 cm included 167 patients (82%), mean age 50.5±18.5. The group with a distance more than 4 cm showed a statistically significant difference in weight, BMI, biceps girth, and number of cords identified in comparison to patients with a distance less than 4 cm (Table II). The power of the study, calculated by the post hoc analysis, for each dependent variables examined, was found to be greater than Discussion and conclusions Sono-anatomy is a science pertaining to different disciplines; it was initially applied in anatomy and radiology, but many other medical specialties are now using ultrasound assistance for diagnostic and therapeutic interventions. Most studies in the last ten years have shown the utility and functional capacity of ultrasound guidance in performing loco-regional anesthesia, altering it from a blind to a visible technique. Ultrasound allows for the identification of internal structures and appropriate anesthetic injection location, and thanks to technical improvements and refining of the method, ultrasound guide of regional anesthesia has been shown to have numerous advantages. 1, 6, 12 These advantages have become particularly evident especially in the performance of infraclavicular block. The best highlighting of anatomical structures has made this block safer and easier, 6, 8 (although studies with large number of patients are required to determine efficacy in the prevention of complications). 6 In particular, compared to triple-stimulation axillary block, ultrasound-guided infraclavicular block provided a similar efficacy in shorter performance time and lower procedural pain scores, 5 and, using ultrasound instead of electrical stimulation, local anesthetic injection cranioposterior to the artery appears feasible. 7 Nevertheless, some loco-regional anesthetic procedures do fail 7, 13 this could be explained by the limits of the two-dimensional ultrasound imaging, 14 difficulties in highlighting the needle tip, 15 and, we suppose, anatomical variability among patients. Thus, we performed an anatomic study using ultrasound identification of neural structures in relation to anthropometric characteristics of a population sample, and attempted to determine if difficulties with ultrasound visualization could be predicted based on physical-anthropometric characteristics. Therefore, the study was designed to detect if there are anthropometric conditions that can restrict the infraclavicular block execution. Other authors have already postulated the potential utility of this type of study The mean difficulty in the execution of this type of study is to standardize a technique of ultrasound visualization of the anatomical structures. Vol No. 4 MINERVA ANESTESIOLOGICA 453

5 DI FILIPPO Ultrasound identification of nerve cords in the infraclavicular fossa: a clinical study We study the visibility of the nerve after getting the best possible image with minimal movements of the probe; we use reproducible measures instead of subject dependent interpretation techniques; furthermore, we use standardized ultrasound probes and settings, according to literature references, which can be reproduced and maintained constant during the study; finally, we use a dual interpretation of expert anesthesists to minimize the possibility of mistake. The main limitation of the study is certainly due to the interpretation of images. In particular the need to use a frozen image loses a little clarity in the field, but the solution was needed to provide double evaluation, more standardized, of the position of the cords. Our results showed that, regarding the position of neural structures, the arrangement of the three cords is quite variable, even if the classic schema with the posterior cord on the lower pole of the artery and the medial and the lateral cords on the sides is substantially maintained. In a small but significant percentage of patients (8.9%) the medial and the lateral cords are shown at the top of the artery, combined. This position, that was unexpected, and which could make it difficult to find structures with peripheral nerve stimulation, may account for the significant number of failures in the execution of this block before the introduction of ultrasound guidance in clinical practice. The position of the cords that we have mentioned before has not previously been described in the literature. Actually, from an anatomical point of view, it can not be considered a variant, since it is likely due to the two branches that join to give rise to the median nerve. This union occurs at the beginning of the axillary area, very close to the probe position, and it is possible that, in some patients, it will be visible even more rostrally. Even if we cannot consider this pattern an anatomical variant, it could be called a sono-anatomic variant and it may represent an avoidable cause of block failure with direct view of the infraclavicular space. A second finding to point out is that the field visibility correlates with anthropometric characteristics (Figure 1A, B). These findings suggest that in high BMI patients, regional anesthesia could be more easily carried out with a mixed technique (nerve stimulator + ultrasound) so that, once the artery is echo or echo Doppler-identified, we can search in the nearby areas for evocation of limb movement, in order to precisely localize the nerve and the best injection site. Our study shows variability of the number of visible veins, even if limited. This resulted in increased risk of hematoma and intravascular injection before the introduction of ultrasound guidance. The ultrasound machine has certainly widened the safety margins by allowing for avoidance of many of these complications. Finally we considered the distance between the upper part of the artery and the apical corner of the ultrasound image. This distance correlates with the anthropometric parameters we analyzed and allows us to conclude that in patients with a high BMI, it is an advantage to initiate the procedure with needles longer than those commonly used (equal to 5 cm), in order to avoid additional punctures, leading to patient discomfort and increased risk of vascular lesions and block failure. References 1. Marhofer P, Harrop-Griffiths W, Kettner SC, Kirchmair L. Fifteen years of ultrasound guidance in regional anaesthesia: part 1. Br J Anaesth 2010;104: Sanchez HB, Mariano ER, Abrams R, Meunier M. Pneumothorax following infraclavicular brachial plexus block for hand surgery. Orthopedics 2008;31: Crews JC, Gerancher JC, Weller RS. Pneumothorax after coracoid infraclavicular brachial plexus block. Anesth Analg. 2007;105: Greher M, Retzl G, Niel P, Kamholz L, Marhofer P, Kapral S. Ultrasonographic assessment of topographic anatomy in volunteers suggest a modification of the infraclavicular vertical brachial block. Br J Anaesth 2002;88: Tran de QH, Clemente A, Tran DQ, Finlayson RJ. A Comparison Between Ultrasound-Guided Infraclavicular Block Using the Double Bubble Sign and Neurostimulation- Guided Axillary Block. Anesth. Analg. 2008;107: Klaasted O, Sauter AR, Dodgson MS.. Brachial Plexus block with or without ultrasound guidance. Current opinion in Anaesthesiology 2009; 22: Sauter AR, Dogston MS, Stubhaug A, Halstensen AM, Klaastad Ø. Electrical nerve stimulation or ultrasound guidance for lateral sagittal infraclavicular blocks: a randomized controlled, observer blinded, comparative study. Anesth Analg 2008;106: Sandhu NS, Capan LM, Ultrasound-guided infraclavicular brachial plexus block. Br J Anaesth 2002; 89: Bigeleisen PE: The bifid axillary artery. J Clin Anesth 2004;16: MINERVA ANESTESIOLOGICA April 2012

6 Ultrasound identification of nerve cords in the infraclavicular fossa: a clinical study DI FILIPPO 10. Cadvar S, Zeybek A, Bayramicli M. Rare variation of the axillary artey. Clin Anat 2000;13: Jurjuris AR, Correa-De-Aruaujo R, Bohn RC. Bilateral double axillary artery: embryologic basis and clinical implication. Clin Anat 1999;12: Marhofer P, Greher M., Kapral S. Ultrasound guidance in regional anesthesia. Br J Anaesth 2005;94: Gürkan Y, Acar S, Solak M, Toker K. Comparison of nerve stimulation vs. ultrasound-guided lateral sagittal infraclavicular block. Acta Anaesthesiol Scand 2008;52: Clendenen SR, Riutort K, Ladlie BL, Robards C, Franco CD, Greengrass RA. Real-time three-dimensional ultrasound-assisted axillary plexus block defines soft tissue planes. Anesth Analg 2009;108: Chin KJ, Perlas A, Chan VW, Brull R. Needle visualization in ultrasound-guided regional anesthesia: challenges and solutions. Reg Anesth Pain Med 2008;33: Van Geffen GJ, Moayeri N, Bruhn J, Scheffer GJ, Chan VW, Groen GJ. Correlation between ultrasound imaging, cross-sectional anatomy, and histology of the brachial plexus: a review. Reg Anesth Pain Med. 2009;34: Moayeri N, Renes S, van Geffen GJ, Groen GJ. Vertical infraclavicular brachial plexus block: needle redirection after elicitation of elbow flexion. Reg Anesth Pain Med. 2009;34: Royse CE, Sha S, Soeding PF, Royse AG. Anatomical study of the brachial plexus using surface ultrasound. Anaesth Intensive Care 2006;34: Acknowledgments. The authors thank Dr. Giacomo Poggi and Dr. Chiara Gonnelli for their contribution in data collection. Received on June 23, Accepted for publication on October 17, Corresponding author: A. Di Filippo, Section of Anesthesia, Department of Critical Care, University of Florence, Careggi Teaching Hospital, Largo Brambilla 3, Florence, Italy. adifilippo@unifi.it This article is freely available at Vol No. 4 MINERVA ANESTESIOLOGICA 455