Anesth Analg 2003;96:862-867
© 2003 International Anesthesia Research Society
REGIONAL ANESTHESIA
An Evaluation of the Supraclavicular Plumb-Bob Technique for Brachial Plexus Block by Magnetic Resonance Imaging
Øivind Klaastad, MD*,
Timothy R. VadeBoncouer, MD ,
Terje Tillung, RT , and
Örjan Smedby, DrMedSci,
*Department of Anesthesiology and
The Interventional Centre, Rikshospitalet University Hospital, Oslo, Norway;
Department of Anesthesiology, University of Illinois at Chicago College of Medicine, Chicago, Illinois; and
Department of Radiology, University Hospital Linköping, Linköping, Sweden
Address correspondence and reprint requests to Ø. Klaastad, MD, Rikshospitalet University Hospital, Department of Anesthesiology, Sognsvannsveien 20, 0027 Oslo, Norway. Address e-mail to oivind.klaastad{at}rikshospitalet.no
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Abstract
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Partly based on magnetic resonance imaging studies, the "plumb-bob" approach for brachial plexus block was designed to minimize the risk of pneumothorax. Nevertheless, the risk of pneumothorax has remained a concern. We analyzed magnetic resonance images from 10 volunteers to determine whether the risk of pneumothorax was decreased with this method. The recommended initial needle direction is anteroposterior through the junction between the lateral-most part of the sternocleidomastoid muscle and the superior edge of the clavicle. If the initial placement is not successful, the brachial plexus may be sought in sectors 20°–30° cephalad or caudad to the anteroposterior line in a sagittal plane through the insertion point. We found that the anteroposterior line reached the pleura in 6 of 10 volunteers without prior contact with the subclavian artery or the brachial plexus, but always with contact with the subclavian vein. To reach the middle of the brachial plexus, a mean cephalad redirection of the simulated needle by 21° was required (range from 41° cephalad to 15° caudad in one case). We conclude that the risk of contacting the pleura and the subclavian vessels may be reduced by initially directing the needle 45° cephalad instead of anteroposterior. If the brachial plexus is not contacted, the angle should be gradually reduced.
IMPLICATIONS: In magnetic resonance images of volunteers, simulated needle passes with the "plumb-bob" approach to the supraclavicular brachial plexus block were analyzed for precision and risk profile. To avoid needle contact with the lung, the subclavian vein, and the subclavian artery, our results suggest a change in the method’s initial needle direction.
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Introduction
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Among all brachial plexus blocks, those with a supraclavicular approach may be most effective at producing complete anesthesia after a single injection (1), but with some risk of pneumothorax. The "plumb-bob" approach by Brown et al. (2) is a modification of the traditional supraclavicular technique. Partly based on magnetic resonance imaging (MRI) studies of volunteers, it was designed to reduce the risk of pneumothorax, with the needle approaching the plexus perpendicularly instead of along the body axis. However, the risk of pneumothorax still remains a concern (3), probably explaining why the method has not become more widespread. The primary objective of this study was to further characterize the anatomy pertinent to the plumb-bob technique.
The plumb-bob approach to the brachial plexus is performed with the patient supine on a horizontal table with the ipsilateral arm at the side and the head turned opposite the side to be blocked (Fig. 1). The point of needle insertion is "immediately adjacent and superior to the clavicle at the lateral-most insertion of the sternocleidomastoid muscle onto the clavicle" (2). The needle direction is anteroposterior—that is, perpendicular to the table—as if following the line of a suspended plumb-bob through the insertion site. Local anesthetic is injected at a single site after adequate paresthesia or motor response by a nerve stimulator (4). If this is not achieved during the initial needle insertion, the needle may be redirected cephalad in small steps maximally to 20° or 30° and subsequently caudad maximally to 20° or 30° while staying in the sagittal plane through the needle entry site (2,3). According to the initial description, it appeared that thin patients usually demanded a cephalad redirection of the needle, whereas a caudad redirection was more often needed in larger patients.
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Figure 1. The figure illustrates how the "plumb-bob" technique for supraclavicular brachial plexus anesthesia is performed (2,3). The point of needle insertion is at the junction between the superior edge of the clavicle and the most lateral part of the sternocleidomastoid muscle. The needle direction is anteroposterior. If brachial plexus contact is not achieved by the initial needle pass, the needle may be redirected cephalad in small steps to maximally 20° or 30° and subsequently caudad to maximally 20° or 30° while staying in the sagittal plane through the needle entry site. The figure is reproduced with kind permission from Dr. Brown and the publisher (Brown DL, Cahill DR, Bridenbaugh DL. Supraclavicular nerve block: anatomic analysis of a method to prevent pneumothorax. Anesth Analg 1993;76:530–4).
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Among the 12 volunteers who were investigated with MRI by Brown et al. (2), the recommended needle direction (the plumb-bob trajectory) never contacted the lung without initially contacting the subclavian artery or the brachial plexus. Particularly in thin subjects with an expected cephalad brachial plexus position, we hypothesized that the risk of pneumothorax might increase. We examined MRIs of the brachial plexus from 10 volunteers investigated at our center (5–7). These images allowed us to position a simulated needle according to the plumb-bob technique in each volunteer.
We evaluated whether the plumb-bob trajectory could reach the pleura without prior contact with the brachial plexus or the subclavian artery. Additionally, we were interested in the precision of the method (how close the initial trajectory came to the brachial plexus) and the possibility of the trajectory contacting the subclavian vein or artery. In a second part, we determined the optimal trajectory (the needle direction reaching the middle of the brachial plexus) for each volunteer and its relationship to the subclavian vessels and the pleura.
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Methods
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After approval of the protocol by the regional ethical committee, 10 healthy volunteers gave their written, informed consent for MRI of their brachial plexus anatomy. They were identical to those participating in three former studies (5–7) and were examined (in one session for all studies) in an open 0.5-T scanner (Signa SP; General Electric, Milwaukee, WI), as described previously (7). The volunteers were in the horizontal, supine position with the arms at the side, as if to receive a plumb-bob brachial plexus block. The shoulders were relaxed, and the head was rotated to the opposite side. The imaging resulted in a three-dimensional data set consisting of 124 T1-weighted sagittal slices of 2-mm thickness. Subsequent mea-surements were made with multiplanar reformatting, permitting arbitrary orientation of the images and simulation of the blocks in each volunteer without the insertion of a needle.
The most lateral sagittal image still demonstrating the sternocleidomastoid muscle insertion on the clavicle was determined. At this sagittal level, an oblique axial plane through the superior border of the clavicle was identified. The intersection between these planes determined the anteroposterior trajectory of the plumb-bob approach to the brachial plexus. The point at which this line contacted the skin anteriorly defined the needle insertion point. Following the initial anteroposterior trajectory in successive coronal planes from the insertion point, we measured the minimum distances to the closest wall of the subclavian vein and artery, to the nearest aspect of the brachial plexus, and to the pleura (Fig. 2). The deviation of the trajectory from the brachial plexus was also described by the angle between the trajectory and the nearest aspect of the brachial plexus, in individual, usually nonsagittal, planes through the trajectory.
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Figure 2. Coronal slice demonstrating how the measurement of two distances from the anteroposterior "plumb-bob" trajectory to the brachial plexus was made. The trajectory is seen as a point or the vertex of the angle. The shortest distance to the brachial plexus is in a nonsagittal plane at approximately 10:30 o’clock, perpendicular to the closest aspect of the brachial plexus, and corresponds to "Distance brachial plexus" in Table 2. The longest distance is in the sagittal plane (at 12 o’clock) to the midaxis of the brachial plexus. This distance was used to calculate the optimal angle of the needle to the plumb-bob, the "Redirection angle" of Table 3. L = lung; c.h. = right caput humeri.
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We further measured the anteroposterior depth from the skin to the closest aspect of the subclavian vein, subclavian artery, brachial plexus, and pleura. If the trajectory did not encounter one of these structures, we recorded the depth at which the trajectory came nearest to the structure. The optimal trajectory was defined in the sagittal plane through the unchanged insertion point by angulating a line through the insertion point in a cephalad or caudad direction to the midaxis of the brachial plexus (Fig. 3). The minimum distances from the optimal trajectory to the subclavian vein, subclavian artery, and pleura were measured, again in successive planes perpendicular to the trajectory.
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Figure 3. Sagittal slice through the point of needle insertion, demonstrating how the angle of the optimal trajectory to the anteroposterior "plumb-bob" line could be measured. The point of needle insertion, the vertex of the angle, is directly on top of the clavicle. The plumb-bob line penetrates the wide lumen subclavian vein, which is seen partly cephalad to the clavicle. The optimal trajectory goes through the midpoint of the brachial plexus, just cephalad to the subclavian artery, having a distinctly smaller lumen than the vein. L = lung; ant = anterior; ceph = cephalad.
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All measured variables are described as mean values and range. Relationships between continuous variables were studied with simple linear regression, and comparisons between groups were made with the Mann-Whitney U-test, both with a significance limit of 0.05.
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Results
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Eight of 10 volunteers were young: in their mid-20s. Most volunteers had a body mass index (BMI) at the low end of normal, and only one volunteer had a BMI above the normal range (defined as 18.5–25.0 kg/m2) (8) (Table 1).
By using the original description, the plumb-bob trajectory encountered the subclavian vein in six and the subclavian artery in two cases (Table 2). The mean anteroposterior depths at which the trajectory touched the anterior wall of the vein or artery or was nearest the vein or artery were 21 mm (range, 17–27 mm) and 34 mm (range, 25–42 mm), respectively. Only in Volunteer 5 did the needle trajectory contact the brachial plexus. The mean distance between the trajectory and the closest part of the brachial plexus was 12 mm (range, 0–22 mm), corresponding to an 18° (range, 0°–34°) deviation. The mean anteroposterior depth at which the trajectory was closest to or encountered the plexus was 35 mm (range, 29–42 mm). Except for Volunteers 5 and 9, the trajectory always passed mediocaudad to the plexus. The degree and direction of the deviation by the trajectory from the plexus were not significantly related to any of the demographic variables in Table 1. If the simulated needle did not stop after contact with the subclavian vein, subclavian artery, or brachial plexus, the trajectory eventually reached the pleura in all but one case (Volunteer 9). In six cases, the trajectory reached the pleura even without prior contact with the subclavian artery or the brachial plexus. In all these cases, however, the trajectory did encounter the subclavian vein. The mean anteroposterior depth at which the trajectory encountered or was closest to the pleura was 43 mm (range, 28–55 mm). Because of the curved surface of the lung and the trajectory’s having a mediocaudad position to the plexus, in three cases (Volunteers 2, 7, and 8) the lung depths were shorter than the plexus depths.
The definition of the optimal trajectory was through the midaxis of the brachial plexus in the sagittal plane through the unchanged insertion point (Fig. 3). This required a cephalad redirection of the needle by a mean of 21° (from 41° cephalad to 15° caudad). The largest cephalad redirection was demanded in the overweight subject, whereas the only volunteer requiring a caudad redirection was thin (Table 3). However, again, the degree of needle redirection and whether it was to be cephalad or caudad could not be predicted from the demographic data. The optimal trajectory’s shortest distance to the pleura was a mean of 6 mm (range, 0–17 mm). It contacted the pleura in two volunteers (5 and 9), but only after a prior contact with the brachial plexus at a shallower depth. Except for Volunteer 7, the optimal trajectory did not encounter the subclavian vein or artery. However, the trajectory was close to these vessels by a mean for all volunteers of 6 mm (range, 0–13 mm) and 3 mm (range, 0–8 mm), respectively.
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Discussion
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Using MRIs without needle insertion in 10 volunteers, we investigated the supraclavicular plumb-bob approach to the brachial plexus. We measured the proximity of the recommended needle direction to the brachial plexus and the following risk structures, in anteroposterior order: the subclavian vein, subclavian artery, and pleura. In particular, we examined whether the trajectory described in the original description of this technique could reach the pleura without prior contact with the subclavian artery or the brachial plexus.
The plumb-bob trajectory very seldom contacted the brachial plexus, usually passing it by 12 mm. The optimal trajectories (touching the middle of the plexus) deviated by a mean of 21° cephalad from the plumb-bob trajectory, with a wide range from 41° cephalad to 15° caudad, by a simulated needle length of 3–5 cm. The degree of the required redirection and whether this redirection was to the cephalad or caudad side could not be predicted from the demographic data. Remarkably, only in a single thin volunteer was a caudad redirection necessary to contact the plexus, and the largest cephalad redirection required was found in the only overweight volunteer. With use of the recommended needle direction, 6 of 10 volunteers would have had the simulated needle touch the pleura without prior contact with the brachial plexus or the subclavian artery. However, in all these cases, the trajectory contacted the subclavian vein before the pleura. Therefore, stopping the needle by recognition of the subclavian vein, subclavian artery, and brachial plexus would prevent it from contacting the pleura in all cases. Even the optimal trajectories passed very close to all risk structures (usually within 6 mm). In two subjects, the optimal trajectory would have contacted the pleura at a depth more than that in which the plexus was contacted.
As for the accuracy of our measurements, the most challenging step in the procedure was the identification of the MRI slice containing the lateral-most part of the sternocleidomastoid muscle. However, with the particular attention paid to this step, we think that the overall accuracy in defining the insertion point in our study was at least equal to the alternative solution: using an MRI contrast marker on the clinically defined needle insertion point and subsequently identifying the marker in the MRIs, as done in the study by Brown et al. (2). The possibility of contacting the subclavian vein supraclavicularly when using an anteroposterior needle direction disagrees with the conventional anatomic teaching that the subclavian vein does not rise above the cephalad border of the clavicle. However, Woodburne’s (9) statement that "the subclavian vein describes the same curving course through the inferior portion of the posterior cervical triangle as does the subclavian artery" fits our findings.
Our results differ substantially from the original description (2). In the 12 volunteers in their study, the plumb-bob trajectory never reached the pleura without contacting the subclavian artery or brachial plexus. Their best-case needle directions deviated from the plumb-bob trajectory by a mean of only 1° caudad (range from 29° caudad to 15° cephalad), and there appeared to be a trend toward heavier subjects requiring a more caudad needle direction. They did not make measurements regarding the subclavian vein. The difference in results between the two studies is difficult to explain. The variation within the population may not have been represented by either study, with small numbers of volunteers examined. Most of our volunteers were in their 20s, and age was not stated in the original study. Most of our volunteers were thin, with a mean BMI of 21.9 kg/m2 (range, 18.8–29.5 kg/m2). However, calculations on demographic data from the original study indicate that the original group was not significantly heavier, with a mean BMI of 23.9 kg/m2 (range, 18.7–31.6 kg/m2). The different methods of defining the skin entry site may have given slightly different sagittal planes for analysis. Although in both studies the volunteers were positioned as if to undergo a plumb-bob brachial plexus block, there may have been variations in the cephalocaudad position of the clavicle.
The frequency of contact between the plumb-bob trajectory and the subclavian vein, the subclavian artery, or the pleura found in our study suggests changing the direction of the initial needle pass from anteroposterior to cephalad. VadeBoncouer and Weinberg (4) have already systematized such a modification on the basis of anatomical considerations and clinical experience. They maintain the insertion point and movement of the needle in the sagittal plane through the insertion point as in the original method but direct the needle a priori at a 20°–30° cephalad angle to the plumb-bob line. On demand, they subsequently reduce this angle until plexus contact is achieved, if necessary also continuing redirections to the caudad side. Our study supports this method, with the addition that one could increase the angle of the initial needle pass to approximately 45°. We are then considering the anatomical variation represented by one of our volunteers, who required a 41° cephalad redirection to contact the middle of the brachial plexus. Another alternative would be to make the insertion point more cephalad or lateral. Moving the insertion site approximately 2.0 cm cephalad to the palpable interscalene cleft and maintaining the anteroposterior needle direction would correspond to the parascalene technique of brachial plexus anesthesia described by Vongvises and Panijayanond (10) and Vongvises and Beokhaimook (11).
Our study demonstrates that, when the plumb-bob technique is performed, the subclavian vein, subclavian artery, and brachial plexus may function as warning structures that the needle is approaching the lung. Therefore, we underline the importance of continuous suction on the needle and the recognition of brachial plexus paresthesia or motor responses from a well functioning peripheral nerve stimulator.
The findings of our small study may not be valid for adults with a different demographic status and especially not for children. Because this work was merely by MRI, it should be confirmed by a clinical investigation.
In conclusion, our MRI study shows that when using the original plumb-bob approach for brachial plexus anesthesia, the needle may contact the pleura, the subclavian vein, or the subclavian artery. The risk may be reduced by initially directing the needle 45° cephalad instead of anteroposterior and, on demand, successively reducing this angle until satisfactory brachial plexus contact is achieved.
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Acknowledgments
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For better understanding of the brachial plexus anatomy, parallel to our MRI studies, we performed human cadaver dissections on the brachial plexus. We thank Stiftelsen Sophies Minde of the National Hospital Orthopedic Center for grants to finance these dissections. We thank Professor Per Brodal at the Department of Anatomy, University of Oslo, for encouraging discussions and cooperation with the dissections. We are also indebted to Professors Erik Fosse and Harald Breivik for constructive suggestions.
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References
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- Lanz E, Theiss D, Jancovic D. The extent of blockade following various techniques of brachial plexus block. Anesth Analg 1983; 62: 55–8.[Abstract/Free Full Text]
- Brown DL, Cahill DR, Bridenbaugh DL. Supraclavicular nerve block: anatomic analysis of a method to prevent pneumothorax. Anesth Analg 1993; 76: 530–4.[Abstract/Free Full Text]
- Brown DL, Bridenbaugh DL. The upper extremity: somatic block. In: Cousins JM, Bridenbaugh PO, eds. Neural blockade in clinical anesthesia and management of pain. Philadelphia: Lippincott-Raven, 1998: 355–7.
- VadeBoncouer TR, Weinberg GL. Supraclavicular brachial plexus anesthesia using the plumb bob method. Techniques Reg Anesth Pain Manage 1997; 1: 151–8.
- Klaastad Ø, Lilleås FG, Røtnes JS, et al. Magnetic resonance imaging demonstrates lack of precision in needle placement by the infraclavicular brachial plexus block described by Raj et al. Anesth Analg 1999; 88: 593–8.[Abstract/Free Full Text]
- Klaastad Ø, Lilleås FG, Røtnes JS, et al. A magnetic resonance imaging study of modifications to the infraclavicular brachial plexus block. Anesth Analg 2000; 91: 929–33.[Abstract/Free Full Text]
- Klaastad Ø, Smedby Ö. The supraclavicular lateral paravascular approach for brachial plexus regional anesthesia: a simulation study using magnetic resonance imaging. Anesth Analg 2001; 93: 442–6.[Abstract/Free Full Text]
- Kottke TE, Clark MM, Aase LA, et al. Self-reported weight, weight goals, and weight control strategies of a Midwestern population. Mayo Clin Proc 2002; 77: 109–13.[Free Full Text]
- Woodburne RT. Essentials of human anatomy. New York: Oxford University Press, 1978: 179.
- Vongvises P, Panijayanond T. A parascalene technique of brachial plexus anesthesia. Anesth Analg 1979; 58: 267–73.[Abstract/Free Full Text]
- Vongvises P, Beokhaimook N. Computed tomographic study of parascalene block. Anesth Analg 1997; 84: 379–82.[Abstract]
Accepted for publication October 21, 2002.
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Abstract
Introduction
