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ANALGESIA

The Influence of Arm Abduction on the Anatomic Relations of Infraclavicular Brachial Plexus: An Ultrasound Study

Ana Ruíz^*, Xavier Sala^*, Xavier Bargalló, Paola Hurtado^*, Maria Jose Arguis^*, and Ana Carrera

From the Departments of *Anesthesiology, Radiology, University of Barcelona, Hospital Clinic of Barcelona, Barcelona, Spain; Department of Human Anatomy, University of Barcelona, Barcelona, Spain.

Address correspondence and reprint requests to Dr. Ana Ruiz, Department of Anesthesiology, University of Barcelona, Hospital Clinic, Barcelona., Villaroel, 170., 080036 Barcelona, Spain. Address e-mail to 32455arp{at}comb.es.

Abstract

BACKGROUND: Distances from brachial plexus to the coracoid process and the pleura are critical for performing infraclavicular block. We evaluated the influence of arm abduction on the position of the neurovascular bundle relative to the skin, to the coracoid process and to the pleura using ultrasonography.

METHODS: An ultrasound examination of the brachial plexus at the infraclavicular level was performed on 26 patients. Distances from the axillary artery to the skin, to the coracoid process and to the pleura were measured and noted with different degrees of arm abduction (0°, 45°, and 90°). Vertical infraclavicular brachial plexus block was then performed by means of nerve stimulation in 14 additional patients undergoing hand surgery.

RESULTS: Under ultrasound examination, the distance from the axillary artery to the skin was found to be significantly less with arm abduction (0°: 32 ± 7 mm, 45°: 29 ± 7 mm, 90°: 25 ± 5 mm, P < 0.05). The distance from the skin to the pleura was 47 ± 5 mm with a medial deviation of 18 ± 3 degrees and was not influenced by arm position. Brachial plexus was identified by nerve stimulation at a vertical depth of 41 ± 7 mm from the skin.

CONCLUSION: Abduction of the arm reduces the depth of the brachial plexus but does not change the position of the axillary artery relative to the coracoid process or the pleura. Ultrasonography may under-estimate the actual depth of the plexus.

Most infraclavicular approaches for brachial plexus block use the coracoid process as an anatomic landmark. The neurovascular bundle passes immediately inferior to the coracoid process, which moves with arm abduction. The insertion site for vertical infraclavicular block is a defined distance from the coracoid process, varying from 1 to 3 cm with different vertical infraclavicular approaches.1–4

Our primary objective was to evaluate the influence of arm abduction on the depth and the position of the brachial plexus relative to the coracoid process and to the pleura using ultrasonography. A secondary aim was to compare the depth of the brachial plexus estimated by ultrasonography with the actual depth of motor response when performing an infraclavicular brachial plexus block using a neurostimulation technique.

METHODS

After obtaining Ethics Committee approval and patients' written informed consent, 40 patients were enrolled in the study. A portable ultrasound machine (Titan, Sonosite; Bothell, WA) and a linear multifrequency probe (38 mm broad linear array transducer) of 10–5 MHz (L38; Sonosite; Bothell, WA) were used in all patients.

The patients were positioned supine with the face turned to the contralateral side. The long axis of the ultrasound probe was positioned in an oblique sagittal plane of 45° (over a line traced between the coracoid process and the xiphoid appendix of the sternum) (Fig. 1A).

View larger version (56K): [in this window] [in a new window]   Figure 1. (A) Probe position for ultrasonographic evaluation. A: Coracoid process. B: sternum. (B) Distance taken between the skin and the middle point of the axillary artery and also to the central point of the coracoid process. (C) Measurements taken from the central point of the artery and from the skin to the pleura. SA (safety angle), DAA (distance from skin to central point of the axillary artery), PAAD (distance from pleura to axillary artery), SPD (distance from supposed puncture site to the pleura).

We used the axillary artery as a surrogate marker because the brachial plexus at the infraclavicular level is difficult to locate.

We measured the depth of the axillary artery (distance between the skin and the central point of the axillary artery), coracoid-axillary artery distance (distance between the most superficial point of the coracoid process and the central point of the axillary artery) (Fig. 1B), distance from the pleura to the axillary artery, and distance between the supposed puncture site of the skin to the pleura and the safety angle to avoid pleura puncture (Fig. 1C). Measurements were performed with the arm in an abduction positioning of 0°, 45°, and 90°.

After ultrasonographic evaluation, vertical infraclavicular brachial plexus block was performed by means of nerve stimulation in 14 additional patients scheduled for hand surgery. The arm was positioned in an abduction of 0°. The stimulating needle (Stimuplex D 50 mm; Bbraun; Melgunsen, Germany) was introduced 27 mm medially to the coracoid process over the line previously described between the coracoid process and the xiphoid appendix.

A depth of 35 mm was chosen for the needle, inserted perpendicularly, which was the sum of what we found to be the average depth (32 mm ± 7 mm) plus 3 mm to allow for the pressure exerted by the transducer.

The nerve stimulator (NHS, Braun; Melgunsen, Germany) was initially set to deliver a pulse duration of 100 µs and a frequency of 2 Hz. The intensity of stimulation was progressively increased until 2 mA or until elicitation of an evoked motor response of the branches of the brachial plexus. We varied the depth of the needle in the same sagittal plane with incremental medial and lateral needle movements of <15° to obtain a satisfactory response with intensity below 0.5 mA. The needle walked along the line shown on Figure 1A. Forty milliliter of 1.5% mepivacaine was injected with a single-injection technique and the block was evaluated at 30 min after injection by the pinprick method in the cutaneous distributions of musculocutaneous (lateral cord), radial (posterior cord), and ulnar (medial cord) nerves.

The SPSS 10.0 statistical package was used for statistical data analysis. Distances are expressed as mean ± sd (sd) in each position of the arm. To determine the optimal position for the procedure, a dispersion analysis was made. Analysis of covariance test followed by a Bonferroni test were done to make multiple comparisons among the different arm positions. A P value of <0.05 was considered statistically significant.

RESULTS

Twenty-six patients, 13 men and 13 women, with a mean age of 31 ± 7 yr, mean weight of 67 ± 13 kg, and mean height of 169 ± 10 cm were included in the ultrasound examination group. Arm abduction significantly reduced the distance between the skin and central point of the axillary artery (Table 1). There were no changes in the other calculated variables.

Vertical infraclavicular block, as previously described in methods section, was performed on the additional 14 patients (7 women and 7 men), with a mean age of 44 ± 20 yr, mean weight of 66 ± 11 kg, and mean height of 166 ± 11 cm. Patients were positioned supine with the arm in 0° abduction. At a depth of 35 mm, a motor response with a mean intensity of 0.57 ± 0.15 mA was elicited in 8 patients. In four patients, the response obtained was the posterior cord and in the other four patients, the lateral cord. Final position of the needle was at a depth of 41 ± 7 mm with motor stimulation in all patients at a mean intensity of 0.3 ± 0.1 mA (lateral cord response in 77% and posterior cord response in the remaining 23%). Thirty minutes after local anesthetic injection, incomplete block of the posterior cord was observed in 2 patients (14%), lateral cord in 3 patients (21%), and medial cord in 6 patients (43%). A single case of vascular puncture was detected. No other complication was observed.

DISCUSSION

The axillary artery is easily identified by ultrasonography and is a basic landmark for ultrasound-guided infraclavicular block.4–10

We found a statistically significant difference in the distance from the skin to the axillary artery (and therefore, in the depth of the brachial plexus), associated with arm abduction, with the neurovascular bundle becoming more superficial as we increased the abduction to 90°.

The depth and position of the lung did not change with arm abduction. The depth of the neurovascular bundle was consistently under-estimated by ultrasonography compared to using stimulation. This may be explained by the compression of the tissues of the chest wall exerted by the probe.

It has recently been reported that the posterior and medial cords are slightly deeper than the artery and that the lateral cord presents a great variability in its depth.11

Likewise, Cornish and Nowitz12 used magnetic resonance imaging with four parasagittal sections medial to the coracoid process in order to measure the plexus depth. Our study was done with ultrasonography studying an oblique sagittal plane which makes the comparison of both studies difficult. Nonetheless the insertion site in our study would correspond to the parasagittal plane 31 mm medial to the coracoid process. At this point, the depth of the plexus was 42 ± 13.4 mm, very similar to our findings (41 ± 7 mm).12 We believe that the distance in our study was under-estimated by ultrasound. The distance to the pleura analyzed by Cornish and Nowitz12 was longer because it considered only the pure parasagittal plane. However, this distance is reduced as the parasagittal plane becomes more medial to the coracoid process. The sagittal plane did not permit assessment of the changes in medial angulation of the needle. In our study, the oblique parasagittal plane allowed us to calculate the minimal distance from the skin to the pleura and the angle needed for the needle to make contact with the pleura.

Bigeleisen and Wilson's4 study provided further information on the effects of arm abduction. However, the plane of study is still purely parasagittal. As we also found, they reported that arm abduction significantly reduces the distance from the skin to the artery.

The main limitations of this study are that ultrasound examination and infraclavicular block were performed in different samples of patients and that we assumed that the depth of the axillary artery is equal to that of the brachial plexus.

We conclude that the distance from the coracoid process to the infraclavicular neurovascular bundle remains relatively constant in the oblique parasagittal plane regardless of the positioning of the arm in different grades of abduction. The depth of the plexus is reduced with the abduction of the arm. Finally, the safety depth of needle insertion to avoid contact with the pleura is 50 mm with a needle deviation of 17 degrees in the medial direction. The depth of the lung does not change with arm abduction but we should consider the anthropometric variables of the patient.

Footnotes

Accepted for publication August 14, 2008.

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