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Anesth Analg 2005;100:1184-1188 © 2005 International Anesthesia Research Society doi: 10.1213/01.ANE.0000144418.15767.C8
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Abstract |
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In this study we examined the anatomy of the infraclavicular region to assess the possibility of estimating brachial plexus depth before performing an infraclavicular block, by using readily identifiable landmarks such as the coracoid process (CP) and the clavicle (CL). Four parasagittal planes across the infraclavicular region were analyzed in 21 individual series of magnetic resonance imaging studies. Measurements included distance to the plexus from the skin of the anterior chest wall, position of the plexus relative to the CL, and clavicular width. The brachial plexus is located directly below the CL in the parasagittal plane 1 cm medial to the CP. If one inserts a needle in this same plane at a point in line with the inferomedial edge of the CP, then plexus depth can be estimated as follows. If the needle is raised, as a whole, straight up from the planned point of insertion to be level with the top of the CL, then the distance from the tip of the needle to a point midway across the width of the CL is equivalent to the distance from the insertion point to the plexus. Furthermore, not only is it uncommon to find the lung in this same parasagittal plane, but when it does appear, it is well behind the plexus. Estimating plexus depth, or "depth gauging," in the infraclavicular region is achievable and is a potentially useful strategy. Further study is required to confirm this finding in the clinical environment.
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Infraclavicular approaches to the brachial plexus have gained popularity in recent years because of the belief that there is greater clinical efficacy than the traditional axillary approach without incurring a major risk of pneumothorax (1–4). The concept of "depth gauging" the brachial plexus from a supraclavicular technique was established in previous work (5). This demonstrated the ability to estimate plexus depth via projections from surface landmarks, principally the clavicle. We analyzed the infraclavicular region (Fig. 1) to determine whether the same concept can be applied to an infraclavicular approach to the brachial plexus.
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Methods |
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With IRB approval, 21 magnetic resonance imaging studies of the shoulder, judged to have normal infraclavicular anatomy by a radiologist, were accessed from the radiological archives. Four separate parasagittal sections were analyzed in each series (Fig. 2A); they were selected for their reliability as points of reference between the different series.
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- Through the midpoint of the coracoid process (CP).
- Through the medial edge of the CP.
- One centimeter medial to the CP.
- The shallowest point of the infraclavicular brachial plexus, i.e., where it came closest to the skin of the anterior chest wall. This point was several centimeters medial to the CP and was used only as an extra plane of reference because there is no surface landmark to accurately identify it. It does, however, provide invaluable information on the more medial anatomic relationships.
The following measurements were made in each of these positions (Fig. 2B):
- Horizontal distance (HD) from the skin of the anterior chest wall to the brachial plexus.
- Vertical distance (VD) from the top of the clavicle to the brachial plexus.
- Distance, horizontally, of the center of the brachial plexus from a vertical line dropped down through the center of the clavicle. We called this the divergence (DIV). The plexus anterior to the vertical line was a negative value; the plexus posterior to the vertical line was a positive value. The less the DIV, the more centered the plexus underneath the clavicle and the greater the potential for depth gauging.
- Location of the brachial plexus relative to the CP in Position 1.
- Width of the clavicle.
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Results |
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Twenty-one individual magnetic resonance imaging series were analyzed, with a predominance of women (8 men and 13 women). All subjects were adults, with height averaging1.68 m (range, 1.55–1.85 m) and weight averaging 74 kg (range, 52–103 kg).
Both HD (Table 1, Fig. 3A) and VD(Table 1, Fig. 3B) showed linear relationships (r2 = 0.97 and r2 = 0.98, respectively) across the infraclavicular region. The brachial plexus passes inferior and posterior to the tip of the CP (Table 2).
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DIV was smallest in Positions 1 to 3—especially Position 3 (Table 1, Figs. 4 and 5). DIV was largest in Position 4 (Table 1, Figs. 4D and 5). Clavicle width was largest in Positions 1–3 and least in Position 4 (Table 1).
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The broader clavicle in Positions 1–3, combined with the small DIVs, indicates that the plexus is centered beneath the clavicle in these positions, most exactly in Position 3 (Fig. 5). The narrower clavicle in Position 4, combined with the larger DIV in the same position, meant that the plexus was not centered beneath the clavicle in this position. In fact, it tended to lie posterior to the clavicle (Figs. 4D and 5).
Brachial plexus depth can therefore be estimated as follows: the plexus lies directly inferior to the clavicle in the parasagittal plane (PSP) 1 cm medial to the CP. If an injection is made in this PSP, level with the inferomedial edge of the CP, the depth of the plexus (shown as "actual depth" in Fig. 6A) will be the same as the "estimated depth" shown in Figure 6A. This is a simple application of geometric principles, because actual depth and estimated depth are the equivalent sides of a rectangle. Estimated depth can be measured because it projects from the clavicle. In practice, we used a simple template similar to the one in Figure 6B to derive this information. There is greater risk of encountering a lung as one moves medially (Table 3), because it appears in the field more frequently and is closer to the skin, and the distance between the plexus and the lung is less.
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Discussion |
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The brachial plexus runs in a straight line, downward and backward, across the infraclavicular region of the upper chest and passes below the inferior margin of the CP. Our study shows that in the course of this journey, the brachial plexus lies directly inferior to the lateral third of the clavicle; the relationship is most exact 1 cm medial to the CP. There is potential to manipulate this relationship to clinical advantage.
The clavicle is a buttress for the shoulder girdle and connects the sternum to the scapula. It is sigmoid shaped, and its broad, flat lateral end is connected to the cylindrical medial end by a curving midsection. The midsection of the clavicle overlies the brachial plexus, subclavian artery and vein, first rib, and superior aspect of the chest wall, thus, to an extent, obscuring the position and course of these structures.
This study demonstrates the potential to use the clavicle to access the plexus infraclavicularly and to avoid the lung. The consistent spatial relationship between the clavicle and the plexus in the proximity of the CP allows for a simple application of geometric principles to derive an estimate of plexus depth (Fig. 5). This can then be used to guide the actual depth of needle insertion—remembering that, as an estimate, some allowance for error must be accepted. We allow for an error of up to 1 cm; i.e., the plexus may be 1 cm shallower or deeper than our estimate. For reasons discussed below, we do not believe that this poses any threat to the lung.
It is important to realize that this depth-gauging technique works despite the variation in plexus depth (HD) that is evident in Table 1. This is because the spatial relationship between the clavicle and the plexus is independent of HD.
The choice of injection point warrants discussion. To use the depth-gauging technique, injection must be made in the PSP. As the plexus runs obliquely across the chest wall, it will intersect with the PSP approximately 1 cm medial to the inferior border of the CP, hence the point of injection. The data in Table 2 do, however, indicate some variation in the oblique course of the plexus, so the injection point may occasionally need to be a little lower, perhaps 0.5–1.0 cm. Provided that the same PSP is retained, depth gauging will still work.
In terms of the location of the lung, the chest wall curves around posteriorly as one moves across the infraclavicular region. This is confirmed by our data: the more lateral one goes, the less likely that the lung is present, the larger the distance from the skin of the anterior chest wall to the lung, and the larger the distance between the plexus and lung (Table 3). The converse of this statement is also true. Our sole reservation with these comments is that it is difficult to state the exact numeric potential of having the lung present in the plane of needle insertion, given the confidence intervals (Table 3). This, of course, is a function of sample size. Accepting this reservation, in PSP 3, identified as suitable for estimating plexus depth, the lung did not appear often, and when present it was well behind the plexus (Table 3). According to the principle of controlled insertion—when needle insertion is controlled by attention to known plexus depth, it is less likely to be inserted far enough to threaten the lung—the likelihood of encountering the lung can become negligible.
In combination with the earlier depth-gauge study (5), we have also created a map of the brachial plexus in the supra- and infraclavicular regions that was provided by accurate knowledge of the location, depth, and course of the plexus. This can help clinicians to think three-dimensionally as they approach the plexus. We believe that mapping the plexus adds an extra dimension to the "anesthetic line of Grossi" (6), a two-dimensional concept that has been used to facilitate approaches to the plexus and that is represented infraclavicularly by Figure 2B.
How does this analysis relate to the described in- fraclavicular approaches to the brachial plexus (1–4)? Those such as the coracoid block (2) relate closely to the relationships described for Position 3, and, hence, depth gauging could be applied. The vertical infraclavicular block (3) is more medial, closer to Position 4, where the plexus depth cannot be estimated reliably with our technique and where risk to the lung is greatest. It does not apply to the lateral and sagittal technique (7), because although their anatomical plane is between our PSPs 2 and 3, their approach to the plexus is caudad in direction and hence oblique to the axis of the plexus, and it cannot take advantage of the relationship we have demonstrated.
From our analysis, we would suggest that Position 3, i.e., 1 cm medial to the CP, is the ideal PSP from which to approach the plexus infraclavicularly. It is easily located, and the clavicle can be used to accurately gauge the depth of the plexus, well clear of the lung. It must be noted, however, that the study group did not include any subjects with extremes of body mass index or any children, and further study is required to include such patients in our conclusions. We would also add another note of caution because we did not perform any blocks as part of this analysis to demonstrate clinical efficacy.
In conclusion, when preparing for an infraclavicular brachial plexus block, it is possible to estimate brachial plexus depth before needle insertion to facilitate accurate and safe needle placement.
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Footnotes |
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Presented in part at the XXII Annual European Society of Regional Anesthesia Congress, Malta, September 2003.
Accepted for publication August 23, 2004.
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References |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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- Raj PP, Montgomery SJ, Nettles D, Jenkins MT. Infraclavicular brachial plexus block: a new approach. Anesth Analg 1973;52:897–904.
[Free Full Text] - Whiffler K. Coracoid block: a safe and easy technique. Br J Anaesth 1981;53:845–8.
[Abstract/Free Full Text] - Kilka HG, Geiger P, Mehrkens HH. Infraclavicular vertical brachial plexus blockade: a new method for anaesthesia of the upper extremity—an anatomical and clinical study. Anaesthesist 1995;44:339–44.[Web of Science][Medline]
- Neuburger M, Kaiser H, Uhl M. Biometric data on risk of pneumothorax from vertical infraclavicular brachial plexus block: a magnetic resonance imaging study. Anaesthesist 2001;50:511–6.[Web of Science][Medline]
- Cornish PB, Greenfield LJ, O'Reilly M, Allan L. Indirect vs direct measurement of brachial plexus depth. Anesth Analg 1999;88:1113–6.
[Abstract/Free Full Text] - Grossi P. Brachial plexus block: the anaesthetic line is a guide for new approaches. Minerva Anestesiol 2001;67:45–9.[Medline]
- Klaastad O, Smith HJ, Smedby O, et al. A novel infraclavicular brachial plexus block: the lateral and sagittal technique, developed by magnetic resonance imaging studies. Anesth Analg 2004;98:252–6.
[Abstract/Free Full Text]
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