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Dynamic ultrasound-guided, short axis, out-of-plane radial artery cannulation: the 'follow the tip' technique.

Radial arterial cannulation is frequently performed in anaesthesia and intensive care, but can be technically difficult even in experienced hands. We report a case of difficult cannulation where a dynamic two-dimensional (2D) ultrasound technique was employed to successfully cannulate the vessel after a palpation technique attempt resulted in extrusion of an intravascular guidewire through the vessel wall.

Arterial access was required for invasive monitoring for a 45-year-old female who presented with a right temporal lesion for elective neurosurgery. Arterial cannulation using a landmark palpation technique and 20-gauge cannula with guidewire failed. 2D ultrasound short axis imaging with a portable machine (LogiqE, GE, Buckinghamshire, UK) and linear probe (12-LRS, GE, Buckinghamshire, UK) revealed an acute medial turn in the course of the radial artery, which appeared to be responsible for the guidewire extrusion and haematoma seen. Successful cannulation was then achieved by a dynamic ultrasound short axis 'follow the tip' technique. The operation proceeded uneventfully and no complications related to the difficult radial artery cannulation were observed.

This technique first entails cross-sectional visualisation of the radial artery in the midpoint of the sector scan. The operator should identify a straight portion of the vessel by panning the probe proximally and observing no change in the relative medio-lateral position of the vessel in the sonogram. Cannulation in such a section of vessel should minimise the likelihood of failed catheter feed once arterial flashback is obtained. Once inserted subdermally and just under the centre of the probe, the needle tip should be visualised as a hyperechoic dot (Figure 1A). The probe is then moved slightly away from the operator until the tip is not visible. Incremental advancement of the cannula should then bring the tip into the scanning plane (Figure 1B). In this way the proceduralist can be assured that the hyperechoic dot seen in the image is indeed the needle tip, rather than the shaft.

This process is repeated in a stepwise fashion until the tip is seen in the lumen of the vessel at an insertion angle that leaves an adequate length of cannula to feed into the vessel once puncture is achieved (Figure 1C). The authors routinely use longer cannulae (51 mm, 20-gauge Surflo, Terumo, Tokyo, Japan) for this reason, as we have observed that the average insertion distance until flashback tends to be longer than that seen when a palpation technique is used. It should be kept in mind that a steeper insertion angle makes the incident angle of the incoming ultrasound beams less favourable for needle visualisation. Visualisation is particularly difficult when the needle tip is about to pierce the arterial wall, as both structures are hyperechoic. The authors have found that using 'flatten-steepen' movements of the needle can assist in identifying the needle tip in these circumstances when the expected hyperechoic dor is not seen after advancement of the tip into the scanning plane. This manoeuvre brings the needle intermittently into a position where the incident ultrasound beam angle is nearer to 90[degrees].


Once the needle tip is seen in the arterial lumen, our practice is to continue the stepwise advancement and visualisation of the tip further into the lumen, keeping the tip as close to its centre as possible. We believe this step allows an eventual further flattening of the insertion angle of the needle/cannula complex, hence reducing the incidence of failed catheter feed. In the case described, ongoing medio-lateral navigation of the cannula tip 'around the corner' of the medial turn of the radial artery was required once initial flashback was achieved.

Use of ultrasound guidance for radial artery catheter insertion has been well described (1), however practitioners in the quoted studies did not dynamically follow the cannula tip (2). Without this technique it would be impossible to achieve cannulation around 'corners' of a tortuous radial artery. We have observed sonographically that difficult cannulation after attaining an initial successful puncture with a landmark palpation technique is usually for this reason. Such conditions exist in approximately 5% of patients (3). Although number of attempts has limited correlation with the incidence of distal ischaemia (4), haematoma at the puncture site has been associated with radial artery occlusion (3); hence we propose that a dynamic ultrasound-guided method should be used early when arterial cannulation is difficult.

Caption: Figure 1: A) Diagrammatic representation of cannulae, ultrasound scanning plane and radial artery cross section as seen in the accompanying sonogram. The cannula tip is inserted subdermally. B) The ultrasound scanning plane has been removed to capture the cannula tip as it advances closer to the artery. C) The ultrasound scanning plane captures the cannula tip in the lumen of the vessel. Arrow=cannula tip, RA=radial artery.

S. L. Goh

C. O. Tan

L. Weinberg

Heidelberg, Victoria


(1.) Shiloh AL, Sarei RH, Paulin LM, Eisen LA. Ultrasound-guided catheterization of the radial artery: a systematic review and meta-analysis of randomized controlled trials. Chest 2011; 139:524-529.

(2.) Gratrix AP, Atkinson JD, Bodenham AR. Cannulation of the impalpable section of radial artery: preliminary clinical and ultrasound observations. Eur J Anaesthesiol 2009; 26:887-889.

(3.) Brzezinski M, Luiseni T, London MJ. Radial artery cannulation: a comprehensive review of recent anatomic and physiologic investigations. Anesth Analg 2009; 109:1763-1781.

(4.) Slogoff S, Keats AS, Arlund C. On the safety of radial artery cannulation. Anesthesiology 1983; 59:42-47.
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Title Annotation:Correspondence
Author:Goh, S.L.; Tan, C.O.; Weinberg, L.
Publication:Anaesthesia and Intensive Care
Geographic Code:4EUUK
Date:May 1, 2013
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