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© 2001 International Anesthesia Research Society
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Abstract |
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In the supraclavicular lateral paravascular approach for brachial plexus regional anesthesia by Moorthy et al. (Moorthy’s block), the patient is supine with the ipsilateral shoulder displaced anteriorly 5–8 cm. The needle direction is precisely defined in the coronal plane (using a Doppler flowprobe) but not in the sagittal plane. We sought to determine whether the block could be simplified by keeping the shoulder in a neutral position, if the needle direction in the sagittal plane could be more precisely described, and if the risk of pneumothorax appeared acceptably small. These questions were studied by magnetic resonance imaging in 10 volunteers. Volume datasets of the periclavicular region allowed precise positioning of simulated needles. In all volunteers, Moorthy’s block could be performed with the shoulder in a neutral position. The optimal needle trajectory passed 5 mm posterior to the clavicle and was 25° posterior to the coronal plane, never approaching the pleura closer than 18 mm. We conclude that Moorthy’s block can be performed with the shoulder in a neutral position, that more precise instructions for the needle direction can be given, and that the risk of pneumothorax seems minimal. This should be confirmed by a clinical study.
IMPLICATIONS: We studied an established method for brachial plexus block with needle advancement in the chest region in volunteers using magnetic resonance imaging. Our results suggest a simplification of the method and more guidelines for the needle angle to the skin, with a minimal risk for lung injury.
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Introduction |
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Infraclavicular brachial plexus blocks have been designed to block all the major nerves of the brachial plexus while minimizing complications such as pneumothorax or major bleeding (1,2). The supraclavicular lateral paravascular approach for brachial plexus regional anesthesia by Moorthy et al. (3,4) (Moorthy’s method) may be considered an infraclavicular method. Although the needle insertion site is supraclavicular, the target is infraclavicular, at the cords or divisions of the brachial plexus. Compared with other infraclavicular methods (1,2), Moorthy’s method has the advantage of a very flat needle angle to the skin and pleura and therefore a theoretically reduced risk of pneumothorax. Using Moorthy’s method (Fig. 1), the patient is supine with a small sheet rolled under the ipsilateral shoulder, elevating it 5–8 cm, to accentuate the clavicle and the sternocleidomastoid muscle (4). The arm is placed at the side and the head rotated 45° to the contralateral side. A Doppler flowprobe is used to identify and mark the course of the third part of the subclavian artery above the clavicle (just lateral to the clavicular head of the sternocleidomastoid muscle) and the first part of the axillary artery below the clavicle. The point of needle insertion is 2 cm superior to and behind the clavicle and 1 cm lateral to the artery marking. A 5-cm long needle is advanced parallel to the surface marking of the artery, behind the clavicle and toward the axilla, in a caudad, lateral, and posterior direction. A nerve stimulator aids in exact positioning of the needle with the tip caudad to the clavicle.
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In our experience with Moorthy’s method, we have not found anterior displacement of the patient’s shoulder necessary for recognizing the anatomic landmarks and performing the block. Further, we have observed that although the Doppler-derived line to be drawn on the skin defines a precise angle for needle direction in the coronal plane, the optimal needle angle in the sagittal plane remains uncertain.
Our goals were to evaluate Moorthy’s method (with our minor modification of the shoulder position) and to give it a more precise geometric definition. This included confirming that the block may be performed without anterior displacement of the shoulder, evaluating the anatomic precision of the method with respect to a target at cord level of the brachial plexus, suggesting a more precise definition of the trajectory in the sagittal plane, determining whether the recommended needle length of 5 cm is adequate for performing the block and assessing the risk of penetrating the pleura. For the study, we used magnetic resonance imaging (MRI) that easily demonstrates the brachial plexus (5).
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Methods |
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After approval of the protocol by the regional ethical committee, 10 healthy volunteers gave written informed consent for MRI of their brachial plexus anatomy. They were identical to those participating in our two first studies (6,7) and were examined in an open configured MRI scanner (GE Signa SP, 0.5 Tesla; GE Medical, Milwaukee, WI), without the use of any needle. The volunteers were positioned as if they were to receive Moorthy’s block of the right upper extremity (supine with the arms adducted and the head rotated 45° to the opposite side), except that the ipsilateral shoulder was kept in a neutral position instead of being anteriorly displaced. Sagittal images were obtained by using a three-dimensional T1-weighted gradient echo sequence (SPGR), and from these images, multiplanar coronal and axial images were reconstructed. A virtual reality model of each volunteer’s infraclavicular region was thus created. The scanning parameters were: TR 34 ms, TE 15 ms, flip angle 60°, slice thickness 2 mm, matrix 120 x 256, FOV 240 mm x 320 mm, receive bandwidth 12, NEX 1, and number of slices 124. This resulted in a total scanning time of 8 min 46 s.
As a target structure of the procedure we chose the posterior cord of the brachial plexus, which was seen in coronal slices as a nerve structure lying lateral and cephalad to the axillary artery. To determine the relationship between the needle direction (the trajectory) and the posterior cord and the pleura, the point of needle insertion and the final position of the needle tip had to be defined. The first point was determined according to Moorthy’s method, whereas the latter was defined particularly for this study.
In coronal magnetic resonance (MR) images the point of needle insertion was determined by the crossing of two lines (Fig. 2). The first line was lateral and parallel to the midaxis of the subclavian-axillary artery at a distance of 1.0 cm. We assumed that this line corresponds to the Doppler-derived line drawn on the skin using Moorthy’s method 1 cm lateral to the subclavian-axillary artery marking. The second line was superior to and parallel to the superior border of the middle third of the clavicle. Clinically this line is drawn on the skin parallel to the superior border of the clavicle, 2.0 cm above and behind the clavicle (3). To mark this line in coronal MR images, its cephalocaudad distance from the superior border of the clavicle had to be found. The distance was derived from a sagittal slice through the middle part of the clavicle (Fig. 3), selected in such a way that an anteroposterior line drawn through the center of the subclavian artery also abutted the superior border of the clavicle. From the point where the anteroposterior line intersected the skin (the first skin point), a line tangential to the skin in cephaloposterior direction was drawn. On this tangent a second skin point was marked 2.0 cm from the first. The perpendicular distance from the second skin point to the anteroposterior line was the distance between the superior border of the clavicle and its parallel line in the coronal plane.
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The final position of the needle tip was to be located approximately 1 cm caudad to the inferior border of the clavicle, as this is a usual end position of the needle tip using Moorthy’s method (Moorthy, personal communication, 1999). In the coronal plane, this point was determined by drawing a line caudad and parallel to the inferior edge of the clavicle at a distance of 1 cm (Fig. 4). The point at which this line crossed the coronal projection of the trajectory defined the final position of the needle tip. The projection of this point to the coronal slice most distinctly delineating the posterior cord defined the position of the needle tip in the sagittal plane. This coronal slice was assumed to contain the midaxis of the posterior cord. Therefore, the final position of the needle tip was as close as possible to the posterior cord while respecting the recommended trajectory of Moorthy’s method in the coronal plane.
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The actual course of the needle trajectory (behind the clavicle, caudad, slightly lateral and posterior) (Fig. 5) was obtained by first rotating a sagittal plane around an anteroposterior axis through the insertion point until it reached the final position of the needle point. In this plane the line between the needle insertion point and the final position of the needle tip defined the actual course of the needle trajectory. The angle between the trajectory and the coronal plane, the minimum distance to the dorsal aspect of the clavicle, and the simulated needle depth were measured in this plane. The shortest distance between the final needle tip position and the posterior cord was measured in a plane that went through the final position of the needle tip and was perpendicular to the posterior cord (Fig. 6). The shortest distance between the needle trajectory (from the insertion site to the final position of the needle tip) and the pleura was measured in planes perpendicular to the needle trajectory with 1-mm intervals. The results are presented as means ± SD or means (range).
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Results |
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The volunteers, 5 women and 5 men, were 30 ± 9 (24–51) yr old with a height of 175 ± 11 (160–193) cm and a weight of 68 ± 16 (50–102) kg.
Using the best-case needle direction in the oblique sagittal plane of each volunteer, the trajectory was never obstructed by the clavicle, passing 6 (3–9) mm posterior to the dorsal aspect of the clavicle. In this setting, the needle trajectory was slightly posterior to the coronal plane by 26° (20°–33°). The trajectory deviated by 4 (2–6) mm from the target, always lateral to the target. This very small imprecision was solely caused by imprecision in the coronal plane, because in the other plane defining the trajectory (the oblique sagittal plane), the optimal trajectory of each volunteer was used. The length of the simulated needle beneath the skin was 48 (42–53) mm.
The shortest distance between the needle trajectory and the pleura was 23 (18–28) mm. At the needle insertion site and the final position of the needle tip, the shortest distances to the pleura were 28 (20–34) mm and 23 (20–28) mm, respectively. Only 3 patients had a point on the needle trajectory closer to the pleura than the final position of the needle tip, and only by 1 or 2 mm. These results fit with the finding that the distal half of the needle trajectory was practically parallel to the pleura.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Using Moorthy’s method, the needle is advanced behind the clavicle from a supraclavicular to an infraclavicular position with the cords/divisions of the brachial plexus as the target. By using MRI, we have investigated a small modification of Moorthy’s method differing from the original method only with regard to the position of the patient’s shoulder. Whereas the shoulder is displaced anteriorly using the original method, it remains in the neutral position in the modified method.
Our MRI study confirms that the block may be performed without displacement of the shoulder, as the best-case needle direction in the sagittal plane was never obstructed by the clavicle. A problem with the neutral shoulder position may be the narrow space between the insertion site and the patient’s face when handling a needle connected directly to the syringe. Using an extension tube between the needle and the syringe solves this difficulty. We consider having the shoulder in neutral position a simplification of Moorthy’s method, making standardization of the procedure easier.
In the coronal plane the recommended trajectory of Moorthy’s method is derived by using Doppler ultrasound. The results of this study confirm the validity of this approach in defining the proper needle angle in the coronal plane. However, the Doppler markings do not aid in defining the optimal sagittal direction of the needle. In using Moorthy’s point of needle insertion while the patient keeps the shoulders in neutral position, our MRI study suggests passing the needle approximately 0.5 cm posterior to the clavicle. Then the needle would have an approximately 25° posterior angle to the coronal plane. If the nerve stimulator does not confirm optimal position of the needle, one may try a second needle pass immediately behind the clavicle. The last alternative is to direct the needle more posteriorly, but probably no more than 1 cm behind the clavicle, to reduce the risk of pneumothorax.
The risk of pneumothorax can be further reduced by keeping the needle parallel to the chest surface and not directing the needle deeper than the ventral surface of the second rib. Respecting these details, and given our MRI finding that the optimal trajectory has a minimum distance to the pleura of as much as 18 mm, we think that the risk of penetrating the pleura is very small. However, this needs to be confirmed in a clinical study.
To contact the brachial plexus approximately 1 cm caudad to the clavicle, a 5-cm long needle may prove to be too short in a few cases. Of course, the brachial plexus may be reached at shorter lengths with a more proximal target; however, this would demand a larger posterior needle angle to the coronal plane with an increased risk of contacting the pleura.
Angles and distances may be different with the shoulder displaced anteriorly. Therefore our suggestions are meant only for patients having the shoulder in the neutral position.
Finding the recommended needle direction in the coronal plane without the use of a Doppler flowprobe is desirable, but this is outside the scope of the present study.
In conclusion, our MRI study confirms that Moorthy’s block may be performed without the anterior displacement of the patient’s ipsilateral shoulder. With the shoulder in the neutral position, the precision of Moorthy’s modified method is good in the coronal plane. For similar precision in the sagittal plane with minimal risk of pleural penetration, the needle should be directed 0.5 cm behind the clavicle, giving an approximately 25° posterior angle to the coronal plane. In some cases a 5-cm long needle may prove to be too short.
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Acknowledgments |
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We are grateful to Dr. S. S. Moorthy for kindly having demonstrated to us the supraclavicular lateral approach for brachial plexus regional anesthesia on patients and for answering questions about the technique. Radiographer Terje Tillung has been of great help in obtaining the original magnetic resonance images in cooperation with Finn G. Lilleås, MD and Jan S. R
otnes, MD. He also made important measurements. Finally, we acknowledge constructive suggestions from doctors Erik Fosse and Harald Breivik. |
References |
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Raj PP, Montgomery SJ, Nettles D, Jenkins MT. Infraclavicular brachial plexus block A new approach. Anesth Analg 1973; 52: 897–903.
[Free Full Text] - Kilka HG, Geiger P, Mehrkens HH. Die vertikale infraklavikulare Blockade des Plexus brachialis. Anaesthesist 1995; 44: 339–44.[Web of Science][Medline]
- Moorthy SS, Schmidt SI, Dierdorf SF, et al. A supraclavicular lateral paravascular approach for brachial plexus regional anesthesia. Anesth Analg 1991; 72: 241–4.[Web of Science][Medline]
- Fleck JW, Moorthy SS, Daniel J, Dierdorf SF. A comparison of the supraclavicular lateral pararvascular and axillary approaches. Reg Anesth 1994; 19: 14–7.[Web of Science][Medline]
- Van Es HW, Witkamp TD, Ramos LMP, et al. MR imaging of the brachial plexus using a T1-weighted three-dimensional volume acquisition. Int J Neuroradiology 1996; 2: 264–73.
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Klaastad Ø, Lilleås FG, Rotnes 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, Rotnes 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]
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