A target point T, closest to all three cords, should theoretically represent the most suitable position for injection. In a triangle with the vertices L, M, and P, the target point T was derived from the intersection point of the perpendicular bisectors. When T was situated outside the area of the triangle, its position was adjusted to the closest side of the triangle (Fig. 3). Subsequently, an optimal injection site was defined as the average position of all the target points T. The calculated target points T and the average positions of the cords (, , and ) were also plotted graphically. The position of and the distribution of the cords were described by vectors with angles and distances to the center of the artery. Angles were measured in a clockwise direction from 0° (at the anterior position) to 360°. The distances of the cords to were calculated. Measurements and calculations are presented as medians with 5th and 95th percentiles.
The volunteers were 10 women and 10 men with a mean age of 42 yr (sd, 12 yr), mean height of 173 cm (sd, 8 cm), mean weight of 76 kg (sd, 15 kg), and mean body mass index of 25 kg/m2 (sd 4.1 kg/m2). Each volunteer had only one side scanned, but for each gender the right and the left sides were examined equally often.
The position of the cords was determined relative to the artery in the lateral sagittal plane (Fig. 4). The distance from the center of the cord to the center of the artery (presented as median with 5th and 95th percentiles) was 9 (4–18) mm at an angle of 276° (263°–321°) for the lateral cord, 9 (4–12) mm at 236° (189°–261°) for the posterior cord, and 7 (4–11) mm at 159° (90°–290°) for the M cord.
The optimal injection site () and the median positions of the cords (, , and — with median angles and median distance to the artery) are shown in Figure 5. The distance between and the center of artery was 4 mm at an angle 235°. The optimal injection site () had a median distance to the positions (centers) of the lateral, posterior, and medial cords of 7 (3–15) mm, 5 (2–9) mm, and 9 (4–14) mm, respectively.
Analysis of our MRI data in the sagittal plane of the LSIB (6) demonstrated that the cords were found within 2 cm from the center of the artery approximately within 2/3 of a circle. With reference to a clock face (Fig. 1) the cords were distributed between III and XI o’clock. Considering all volunteers, an average point with shortest distances to all cords was found at VIII o’clock, close to the artery, in the cranioposterior quadrant. Injecting at this position may theoretically give efficient local anesthetic distribution to all cords.
Ultrasound guidance has been used frequently to perform brachial plexus blocks (7–9). However, the identification of nerve structures by ultrasound can be difficult in the infraclavicular region (10). Ultrasound visualization of the infraclavicular blood vessels is reliable (11), allowing ultrasound-guided needle placement at the suggested injection site at VIII o’clock. Observing satisfactory distribution of local anesthetic between III and XI o’clock may predict successful blocks.
The anatomy of the plexus varies widely among individuals. Hence, the small number of volunteers is a limitation of our study, and our data might not be representative. Further, our measurements only apply to a sagittal plane (6). We do not know whether the injection site suggested by MRI analyses, derived from scattered individual optimal target sites (Fig. 5), is actually optimal for ultrasound-guided blocks. Our proposals should be confirmed by clinical studies.
1. Kilka HG, Geiger P, Mehrkens HH. [Infraclavicular vertical brachial plexus blockade. A new method for anesthesia of the upper extremity. An anatomical and clinical study]. Anaesthesist 1995;44:339–44.
2. Borgeat A, Ekatodramis G, Dumont C. An evaluation of the infraclavicular block via a modified approach of the Raj technique. Anesth Analg 2001;93:436–41.
3. Deleuze A, Gentili ME, Marret E, Lamonerie L, Bonnet F. A comparison of a single-stimulation lateral infraclavicular plexus block with a triple-stimulation axillary block. Reg Anesth Pain Med 2003;28:89–94.
4. Koscielniak-Nielsen ZJ, Rasmussen H, Hesselbjerg L, et al. Clinical evaluation of the lateral sagittal infraclavicular block developed by MRI studies. Reg Anesth Pain Med 2005;30: 329–34.
5. Koscielniak-Nielsen ZJ, Hesselbjerg L, Fejlberg V. Comparison of transarterial and multiple nerve stimulation techniques for an initial axillary block by 45 mL of mepivacaine 1% with adrenaline. Acta Anaesthesiol Scand 1998;42:570–5.
6. 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.
7. Ootaki C, Hayashi H, Amano M. Ultrasound-guided infraclavicular brachial plexus block: an alternative technique to anatomical landmark-guided approaches. Reg Anesth Pain Med 2000;25:600–4.
8. Sandhu NS, Capan LM. Ultrasound-guided infraclavicular brachial plexus block. Br J Anaesth 2002;89:254–9.
9. Peterson MK, Millar FA, Sheppard DG. Ultrasound-guided nerve blocks. Br J Anaesth 2002;88:621–4.
10. Perlas A, Chan VW, Simons M. Brachial plexus examination and localization using ultrasound and electrical stimulation: a volunteer study. Anesthesiology 2003;99:429–35.
© 2006 International Anesthesia Research Society
11. Galloway S, Bodenham A. Ultrasound imaging of the axillary vein–anatomical basis for central venous access. Br J Anaesth 2003;90:589–95.