Ultrasonographic assessment of topographic anatomy in volunteers suggests a modification of the infraclavicular vertical brachial plexus block{dagger}

M. Greher*,1, G. Retzl2, P. Niel3, L. Kamolz4, P. Marhofer1 and S. Kapral1

1Department of Anaesthesia and General Intensive Care, University Hospital of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria. 2Institute of Anatomy, Department 3, University of Vienna, Waehringerstrasse 13, A-1090 Vienna, Austria. 3Department of Medical Statistics, University of Vienna, Schwarzspanierstrasse 17, A-1090 Vienna, Austria. 4Department of Plastic and Reconstructive Surgery, University Hospital of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria*Corresponding author

{dagger}This article is accompanied by Editorial I.

Accepted for publication: October 16, 2001


    Abstract
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
Background. The infraclavicular vertical brachial plexus block, first described by Kilka and co-workers, offers a more proximal spread of anaesthesia for the upper extremity than the classic axillary approach. In this technique, the puncture site is defined as lying at the exact centre of an infraclavicular line (k) between the jugular fossa and the ventral process of the acromion. Our study was designed to determine whether the point so defined (P) corresponds with the optimal puncture site determined sonographically (S) and to develop an improved prediction model.

Method. High-resolution ultrasonography was carried out in 59 volunteers to visualize the plexus. Sonography-derived distances and morphometric measurements were used to test accuracy and calculate multiple regressions.

Results. We found a clear trend towards a more lateral puncture site. In women, S was significantly (P<0.001) lateral (8 mm) to P. The overall accuracy of the infraclavicular vertical brachial plexus block technique was not sufficient to predict the optimal puncture site reliably. Our resulting improved prediction model is valid for both sexes and is based not just on the centre point but on the absolute length of k (22–22.5 cm). We found that for every 1 cm decrease in k the optimal puncture site moved 2 mm laterally from the exact centre of k, and for every 1 cm increase in k it moved 2 mm medially.

Conclusions. The suggested modification should help to increase the success rate of the infraclavicular vertical brachial plexus block while decreasing the rate of potentially severe complications, although individual ultrasonographic guidance is to be recommended whenever possible.

Br J Anaesth 2002; 88: 632–6

Keywords: anaesthetic techniques, regional; anaesthetic techniques, brachial plexus block; anaesthetic techniques, infraclavicular vertical brachial plexus block; measurement techniques, ultrasonography


    Introduction
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
The infraclavicular brachial plexus block technique has become increasingly popular for the provision of anaesthesia in upper limb surgery.15 The infraclavicular vertical brachial plexus block (IVBPB) developed by Kilka and colleagues5 offers a precisely defined, simple approach: the puncture site lies exactly in the centre of an infraclavicular line between the jugular fossa and the ventral process of the acromion, where the needle is advanced vertically using a nerve simulator. However, because of the close anatomical relationships in this area, potentially serious complications, such as vessel puncture and pneumothorax, can occur.6 7 High-resolution ultrasonography (US) is useful to guide nerve blocks.812 When performing US-guided IVBPB,13 we have often observed the optimal puncture site to be different from that predicted by the IVBPB technique, indicating that the IVBPB technique carries an inherent risk of complications. To our knowledge, there is no sonographic study assessing the topographic anatomy of the infraclavicular region in vivo. Accordingly, we designed a prospective study in volunteers to find out how accurate the IVBPB technique is in predicting the optimal puncture site, and if we can predict the site more reliably with a mathematical model based on morphometric measurements.


    Methods
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
After institutional review board approval and written informed consent, we enrolled 59 healthy volunteers (in one case in which the subject was a minor, parental consent was obtained). Body weight and height were recorded and body surface area (BSA) was calculated according to the method of Dubois.14 The examination was performed by one of two physicians experienced in ultrasonography and the IVBPB technique. Randomization by coin toss determined the side of the body on which the investigation was to be carried out.

The volunteers were placed and remained in the supine position with the elbow flexed to 90° and the palm of the hand lying comfortably on the abdomen, corresponding exactly to the position described by Kilka and colleagues.5 The head, facing forwards, rested on a flat pillow. First, the jugular fossa and the ventral process of the acromion were identified carefully. The latter landmark can sometimes be difficult to distinguish but its exact identification is crucial. Thus, nearby incorrect landmarks (coracoid process, lateral acromion and structures belonging to the head of the humerus, the last confirmed by passive rotation of the shoulder joint) were also identified in all volunteers, and excluded. The jugular fossa and the ventral process of the acromion were marked with a skin pen and joined with a straight line (k) (Fig. 1). After we had measured the length of k with a ruler, the predicted optimal puncture site (P) was located exactly in the middle of k. Then, the distance between the jugular fossa and the caudal top of the mastoid process (m) and the circumference (c) of the neck below the thyroid cartilage were measured to determine by regression whether they might be useful in predicting the optimal puncture site.



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Fig 1 Infraclavicular vertical brachial plexus block (IVBPB). Schematic view based on a real magnetic resonance imaging scan. Landmarks (1=jugular fossa, 2=ventral process of the acromion), the puncture site according to the IVBPB technique (P) and the optimal puncture site are verified by sonography (S).

 
High-resolution US imaging was performed with an ATL Ultramark 9 System (ATL Ultrasound, Bothell, WA, USA) using a 5–10 MHz digital linear array probe 7 cm wide with a mark at its precise centre. The attached Sony video printer and integrated Super VHS video recorder were used for documentation. At the beginning of every US examination, the scanning head was positioned exactly perpendicularly to the skin, with the centre-point scanning head mark exactly on P. By slight rotational movements of the scanning head we looked for the typical US cross-sectional view of the infraclavicular region, which depicts the subclavian artery and vein, the pleura and the cephalic vein (Fig. 2). Colour-flow Doppler and compressibility testing helped to discriminate between the artery and the vein. The cords of the brachial plexus, located cephaloposterior to the subclavian artery, were identified as rounded hypoechoic nodules. If necessary, the scanning head was then moved along k so that its centre-point mark was exactly above the centre of the nerve bundle. This position of the scanning head mark on k was considered the optimal US-verified puncture site (S), and this position was marked on the skin (Fig. 1). The deviation (d) of S from P was measured in millimetres (taking a negative value if S was lateral to P). We classified the results by their clinical relevance, assigning d to the following 13 groups, each of which encompassed an interval of 5 mm: group 0 (–2.5 mm <= d < +2.5 mm); group L5 (–7.5 mm <= d < –2.5 mm); group M5 (2.5 mm <= d < 7.5 mm), ...; group L30 (–32.5 mm <= d < –27.5 mm); group M30 (27.5 mm <= d < 32.5 mm). Finally, other US-determined distances were recorded: skin to centre of subclavian artery; skin to centre of brachial plexus; and centre of brachial plexus to centre of subclavian artery.



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Fig 2 Typical sonographic image of the infraclavicular region (cross-section). Note the proximity to the pleural cavity (arrows). SA=subclavian artery; SV=subclavian vein; CV=cephalic vein; circles=cords of the brachial plexus.

 
Statistical analysis was performed in collaboration with the Department of Medical Statistics, University of Vienna. The one-sample t-test was carried out to test the mean of d against zero for all subjects and separately for men and women. The Pearson correlation coefficient was used to assess the bivariate association between d and k for all subjects and separately for men and women. To analyse the influence of age, weight, height, BSA, c, k and m on d, stepwise linear regression was performed separately for men and women. We assessed bias and accuracy with the Bland and Altman method to visualize the possible bias of the IVBPB technique compared with the sonographic technique to determine the optimal puncture site.15 The SPSS statistical software package was used for the analyses. For stepwise regression analysis, the significance level for a variable to enter or to stay in the model was set at {alpha}=0.05. P<0.05 was considered statistically significant.


    Results
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
Complete data including video prints of the sonographic examinations were obtained for 59 subjects (25 women and 34 men). Their mean age was 33 yr (range 17–91) and mean BSA 1.84 m2. The characteristics and morphometric measurements of the volunteers are presented in Table 1. Sonographic identification of the subclavian artery and vein was possible in all cases. In the majority of cases, it was possible to show the cephalic vein crossing the nerves and the artery ventrally before joining the subclavian vein. US always identified nerve structures that form a bundle, which can be identified unequivocally as the brachial plexus at cord level. Their projection on k defined the US-verified optimal puncture site (S) on the skin in all cases. The mean distances from the skin to the centre of the artery and to the centre of the brachial plexus were less than 30 mm in both sexes (maximum depth 38 mm) (Table 2). In all cases, the cords of the brachial plexus were directly adjacent to the subclavian artery and close to the pleural cavity (Fig. 2).


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Table 1 Characteristics and morphometric data for the volunteers, expressed as mean (SD). k=distance between jugular fossa and ventral process of the acromion; m=distance between jugular fossa and caudal top of the mastoid process; c=circumference of infrathyroidal collar
 

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Table 2 Ultrasonography-derived distances, expressed as mean (SD) in mm. d=deviation of ideal puncture site (S) from IVBPB puncture site (P) in mm; negative values of d indicates that S is lateral to P. *One-sample t-test
 
Figure 3 shows a histogram of deviation d in female and male subjects. A perfect hit (group 0, –2.5 mm <= d < +2.5 mm) was observed in 10 of 59 volunteers (17%; five females and five males). A fair approximation (groups L10 to M10, –12.5 mm <= d < +12.5 mm) was reached in 46 of 59 subjects (78%; 21 females, 25 males). Nevertheless, the mean deviation d differed significantly (P<0.001) from zero in women: the US-verified optimal puncture site (S) was located 8 mm laterally to that predicted by the IVBPB technique alone (P). In men, the same trend towards a more lateral (2 mm) optimal puncture site was found, although the result was not statistically significant (Table 2, Fig. 4).



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Fig 3 Histogram of deviation d in female and male volunteers (L indicates lateral, M indicates medial, numbers indicate distance in intervals of 5 mm).

 


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Fig 4 Box-and-whisker plot of deviation d, separately for men and women. The circle indicates P<0.001 (d vs 0; one-sample t-test).

 
As a result of these findings, separate multiple regressions were performed. Variables d and k were positively correlated (overall r=0.492, P<0.0005; females, r=0.474, P=0.019; males, r=0.395, P=0.023). Stepwise linear regression for d in men was performed using data from the 34 male volunteers. Only k was found to have a significant positive effect (P=0.023). The value of r2 was 0.22. The resulting prediction model for d in men was: dm=–4.332+0.197k. Hence, a deviation of zero in men is predicted when k is 22 cm. An increase of 1 cm in k increases d by 1.97 mm (a medial movement of 2 mm). Stepwise linear regression for d in women was performed using data from the 25 female volunteers. Again, only k was found to have a significant positive effect (P=0.019). The value of r2 was 0.16. The resulting prediction model for d in women was: df=–4.283+0.195k. Hence, a deviation of zero is predicted when k is 22.5 cm. An increase of 1 cm in k increases d by 1.95 mm (a medial movement of 2 mm). In both of the analyses, no other variable was entered into the model because of the lack of previously determined significance.

When the accuracy of the IVBPB was compared with that of the sonographic technique, the Bland and Altman plot (Fig. 5) clearly indicated the bias of the IVBPB technique. The distance d seems not to depend on the mean distance of P and S from the medial landmark (jugular fossa). The second finding of the Bland and Altman analysis was a high degree of variability in d, with a standard deviation higher than the value of d. In one subject in whom there was a large deviation (29 mm), the medial puncture site would have been likely to cause a pneumothorax.



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Fig 5 Bland and Altman plot for the two methods of determining the optimal puncture site. The solid line indicates the mean value of d and the dashed lines indicate the standard deviation.

 
In none of the subjects was the ideal puncture site confirmed by actual puncture.


    Discussion
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
The IVBPB technique was developed and verified primarily in anatomical dissections of cadavers and then applied in the clinical setting. Its success rate in the two published prospective clinical studies (total n=373) is high (up to 90%), and the risk of pneumothorax is considered to be minimal.5 6 However, a case of pneumothorax has been reported in a woman in whom the needle insertion depth was only 35 mm.7 Vessel punctures (up to 30%)6 are seen frequently.

The results of our US study suggest that the IVBPB technique may not be accurate enough in predicting the optimal puncture site. Although the optimal puncture site (S) could be either lateral or medial to P, there is an evident bias in the IVPB technique. We found a clear trend towards a more lateral puncture site in both sexes. In women, the US-verified optimal puncture site was, on average, 8 mm lateral to the point determined by the IVBPB technique alone (P<0.001). We found that we could predict the puncture site more reliably with a mathematical correction that can be simplified as follows: at a k of 22–22.5 cm, the optimal puncture site is identical with the point determined by the IVBPB technique alone; for every 1 cm decrease in k, the ideal puncture site is 2 mm lateral to the point determined by the IVBPB technique, and if k increases by 1 cm it is 2 mm medial to it. Because the mean k in our female volunteers was 18 cm, we measured a mean d of –8 mm in this group.

We strongly recommend the use of US guidance in the IVBPB whenever possible, in order to increase the success rate and to decrease the rate of complications. When US guidance is unavailable, we suggest that the IVBPB technique should be modified according to our mathematical model to predict the optimal puncture site, especially in women. One might argue against the relevance of a deviation of ~1 cm, but we believe that the close relationship of the vessels and the pleura to the brachial plexus (Fig. 2) justifies every improvement in the technique. Furthermore, we recommend that the needle should not be advanced more than 40 mm, at least not in patients within the weight range studied here.

One major limitation of this study in volunteers is the fact that no actual puncture was performed, but a simulated needle insertion was used as a model. Although it would have been more relevant to check for the adequate position of a real needle, we consider this non-invasive model valid to provide basic data because of the strictly vertical approach and our experiences with US guidance in patients.13 Moreover, techniques such as magnetic resonance imaging and high-resolution US in vivo promise more accurate determination of the optimal puncture site than cadaver studies.16 17 However, in contrast to a recent study18 in which only the subclavian artery was depicted, we maintain that visualization of the nerves, which are the target structures, is of utmost importance in precision guidance. Further clinical studies are needed to support our results in practice. Our findings are limited to the study population and are not applicable to children or morbidly obese patients.

In conclusion, we have shown that the overall accuracy of the IVBPB technique in predicting the optimal puncture site might not be high enough. A suggested modification should help to increase the success rate while decreasing the rate of potentially severe complications, although individual US guidance is to be recommended whenever possible.


    Acknowledgement
 
We thank Jane Neuda for editorial assistance.


    References
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 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
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