Department of Anaesthesia, Leeds General Infirmary, Great George Street, Leeds LS1 3EX, UK
Corresponding author. E-mail: andy.bodenham@leedsth.nhs.uk
Accepted for publication: March 19, 2002
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Abstract |
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Method. In 50 subjects, we used ultrasound to examine the infraclavicular regions from below the mid-clavicular point and at 2 cm and 4 cm further laterally (described as the middle and lateral points) with the arms at 0°, 45° and at 90° abduction. We took measurements at each point, with the artery and vein seen in cross-section. The depth from the skin, vessel diameters and the distance between the vessels was measured. The amount of overlap was scaled from 0 (no overlap) to 3 (complete overlap). We also recorded (if visible) the distance between the rib cage and axillary vein. A longitudinal image of the vein was also obtained. Angle of ascent (in relation to the skin), length and depth of the vein was measured.
Results. Axillary vessels were seen in 93% of images. The mean depth from skin to vein increased from 1.9 cm (range 0.73.7 cm) medially to 3.1 cm (1.15.6 cm) laterally. The venous diameter decreased from 1.2 cm (0.32.1 cm) medially to 0.9 cm (0.41.6 cm) laterally. The arteriovenous distance increased from 0.3 cm to 0.8 cm. Median arteriovenous overlap decreased from 2/3 (mode 3/3) to 0 (0). The distance from rib cage to vein increased from 1.0 cm to 2.0 cm.
Conclusion. The axillary vein is an alternative for central venous cannulation and we present an anatomical rationale for its safe use. Less arteriovenous overlap and a greater distance between artery and vein and from vein to rib cage should provide an increased margin of safety for central venous cannulation.
Br J Anaesth 2003; 90: 58995
Keywords: equipment, catheters, venous; measurement techniques, ultrasound
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Introduction |
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We set out to examine the anatomical relationships of the axillary vessels and surrounding structures to guide the safe cannulation of the axillary vein. We wished to confirm that a more lateral approach would have anatomical advantages giving a greater safety because the vein lies at a greater distance from the artery and rib cage, or because the overlap between the vessel changes on moving from medial to lateral. This was purely an observational study.
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Surface landmark techniques |
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A blind landmark-based technique for cannulating the axillary vein was suggested in 1987 by Nickalls and colleagues.1 They studied cadavers and suggested a complex landmark-based approach to the infraclavicular portion of the axillary vein. They described an insertion point three fingerbreadths below the coracoid process slightly lateral to the lateral border of pectoralis minor. The needle is aimed towards the point below the medial end of the clavicle where the space between the clavicle and the thorax just becomes palpable. This is approximately the junction of the medial quarter and lateral three-quarters of the clavicle. Despite this apparently complicated technique they claimed success in 13 out of 14 patients. In a larger study Taylor and Yellowlees2 used a slight modification to this technique using a landmark-based method. The success rate for cannulation of the axillary vein was 96% (similar to that reported for subclavian vein cannulation by Mogil and colleagues3 in 1967).
Neither of the blind surface landmark techniques seems to be widespread. This may be because anatomical variability may reduce reliability. The anatomy of the veins of the upper limbs often varies.4 Cadaver-based studies show that arm position affects the position of the axillary vein1 5 and venogram-based studies show sex differences in axillary vein straightness and diameter.6 The axillary vein and artery often overlap.7 This variation in relationship between the axillary artery and axillary vein is clinically important because axillary vein puncture may be associated with simultaneous arterial puncture if a landmark-based technique is used, with complications.
We used ultrasound to show anatomical variation in a study of femoral vascular anatomy.8
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Applied anatomy |
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Methods |
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Results |
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Of the 50 patients scanned, 41 scans (82%) were complete in terms of visibility of the vessels. Sometimes both vessels could not be seen adequately. The mean BMI of the patients with incomplete scans was 27.2, compared with 25.2 for the patients in whom scanning was complete. In those patients with incomplete scans, it was usually the more lateral scans that were difficult or inconclusive.
The relationships between the various tributaries to the subclavian vein varied. Most often (but not always) the cephalic vein was smaller than the axillary vein and joined it laterally. However, in a small number of cases the cephalic vein arose more medially, appearing in the most medial or middle slices. This occurred in approximately 12% of subjects scanned (Fig. 5).
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The mean depths and diameters of the vessels for the different ultrasound slices and the mean arteriovenous distance are shown in Tables 1, 2, 3. The mean venous diameter with 10° head-down tilt was 1.3 cm. The mean arterial diameter with 10° head-down tilt was 0.8 cm.
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Longitudinal sections
The mean depth of the deepest part of the vein seen on the longitudinal scan was 2.7 cm. The mean angle between the skin and the vein was 13.3° (range 129°).
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Discussion |
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Ultrasound cannot be used to show the subclavian vein as, by definition, this vessel is under the clavicle. It could be used for the supraclavicular approach although this is a less popular technique. Ultrasound aids accurate cannulation of many central veins, reducing complications.9 10 Use of ultrasound for axillary vein cannulation may also reduce complications, as suggested by Doppler studies.11
Safe effective cannulation of the axillary vein by the infraclavicular approach is attractive as it shares the advantages of the subclavian route (clean site, comfortable for patient). In addition, compared with the subclavian vein, there should be less risk of pneumothorax, haemothorax and chylothorax. In the event of inadvertent arterial puncture, a more lateral approach allows direct external pressure to be applied and easier surgical access (the same as for axillo-femoral bypass). Other patients who might benefit from a more lateral puncture include those with tracheostomies, recent sternotomy and those who have midline thoracic burns.
Ultrasound
We did not expect to see the brachial plexus. There is an inverse relationship between depth of penetration of ultrasound and image resolution. We compromised our image resolution in order to achieve adequate depth of penetration so that the vessels would be visible at the greater depths in the lateral sections. Study of these structures has been reported in a recent paper.12
We found considerable variation in the anatomy, which would not be appreciated with surface landmarks. This variation makes the use of ultrasound attractive when accessing these vessels. With other central veins, ultrasound can aid accurate cannulation and hence reduce complications.9 10
Practical application
We examined patients in the ICU as the study was time-consuming and therefore not appropriate for use in more urgent circumstances. In addition, the patients were real rather than volunteers who could have had more favourable characteristics.
We could not see the vessels at all sites in all patients. In only one patient were no vessels visible in any of the scanned areas. Vessels were less easily imaged in larger patients. The mean BMI for the patients with incomplete scans was 27.2, compared with 25.2 for those with complete scans. Satisfactory scans were much harder to obtain from patients with oedema over the anterior thoracic wall. Surgical emphysema makes ultrasound of this region very difficult. It is also of interest that subclinical surgical emphysema was detected in some patients in this way. A permanent pacemaker made probe positioning difficult in one patient.
Overlap of the artery and vein
We found more vessel overlap in the more medial sections. This could cause problems. Needle advancement reduces venous diameter.13 With central venous cannulation, the first aspiration of blood often occurs on withdrawal of the needle,14 15 especially when a narrower gauge seeker needle is not used, probably because the vein is compressed and transfixed.16 This means that if the artery lies behind the vein, then it may be punctured, causing possible haematoma, haemothorax or even arteriovenous fistula. This is a good reason for a more lateral approach.
Depths and angles
We found that the vein would be deeper with a more lateral approach. The mean depth in the most lateral ultrasound slices was 3.2 (range 1.45.4) cm, 3.1 (1.35.1) cm and 3.1 (1.15.6) cm in the midclavicular, 2-cm and 4-cm slices, respectively. At the greater depth higher frequency ultrasound probes, which have limited depth range, will not provide a good image in obese or muscular subjects, and we found this to be a clinical problem.
This depth also requires a much steeper angle of approach with the needle when attempting to cannulate the vein. This increase in depth of the vessels and the more lateral position will affect the length of catheter required, up to 10 cm. This is not a problem for catheters which are cut to length, but for fixed-length catheters a 20 cm catheter (or longer) is likely to be required.
The longitudinal sections show the angle at which the vein rises up from the axilla. It is also worth noting that the skin at this point is also rising up from the axilla onto the anterior rib cage so that the angle of ascent is actually greater than that shown.
Rib cage
We found that the rib cage was less visible in the more lateral slices. In those patients whose rib cage is visible more laterally, the distance between the axillary vein and the rib cage is greater. In fact if we looked for the rib cage it was always visible but often not close to the vessels. This suggests an advantage over the subclavian vein, which is in much closer proximity throughout its length, hence the greater likelihood of pneumothorax with this traditional approach.
Subject position
Tilting the patient 10° head down had no effect on the arterial diameter. As expected, the diameter of the axillary vein was increased by head-down tilt. This increase from 1.2 cm to 1.3 cm is small but may be of clinical significance. More importantly, head-down tilt may increase the venous pressure, which would make cannulation easier and transfixion less likely. Tilting the patient 10° head down did not alter the overlap. The median value was 2/3 (2 for the untilted).
Arm position
There were no differences between the arm positions in terms of visibility of vessels. Generally, different degrees of abduction of the arm had only small effects. Vessel depths and diameters were largely unchanged with increased abduction. There was small but consistent decrease in the distance between the vein and the rib cage. It is not clear if this was caused by abduction, supination or both, as the movements were not distinguished. There does not appear to be any great benefit in the use of one arm position over another.
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Conclusion |
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References |
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