It's not the prick at the distal end of the needle that does the damage
Ultrasound-guided central venous catheter (CVC) insertion is established as a gold standard for the placement of internal jugular vein (IJV) lines and its use has extended to other vascular access sites in adults and children.1–3 Interestingly, as experience in paediatric practice develops, the skills and techniques required seem to differ from adult practice, and high-quality evidence is emerging as these methods are refined.4,5 We are now entering an era in which the scope of ultrasound is expanding and experience relating to the complications, technological improvements, complementary techniques and consequent training requirements is being accumulated.
Ample evidence has demonstrated that, in adults, ultrasound-guided IJV access reduces the incidence of arterial puncture, haemothorax, pneumothorax, and probably catheter-related blood stream infections, while offering improvements in speed of insertion, number of attempts, and success at first attempt.6,7 This is reinforced by guidance from the UK National Institute of Clinical Excellence (NICE guidance 49 2002, http://guidance.nice.org.uk/TA49) and it seems likely that routine use of ultrasound will improve safety at other vascular access sites. International consensus on the use of ultrasound for vascular access now seems appropriate and there are initiatives underway to establish this (www.winfocus.org/world/usva, accessed 29 October 2010).
This month the journal contains two articles exploring the anatomy relevant to ultrasound-guided CVC insertion.8,9 Each report emphasises the importance of understanding and correctly identifying the relevant structures and also reminds us that the anatomy at these sites is inconsistent, and that landmark-based techniques cannot take account of this variability.
Maecken et al.8 explore the anatomical relationship between the right and left IJV and ipsilateral carotid artery during ultrasound examination of the neck. Their study demonstrates that the ultrasound probe cannot easily project a true anterior-posterior image because of the curved surface of the neck and this alters the apparent relative alignment of the vessels. Consequently, they lie in a different orientation to that described for the landmark technique. In practice, clinicians hold the ultrasound probe at 30–40° from the perpendicular to achieve good contact with the skin, causing the IJV to be positioned more anterior to the carotid artery and increasing the risk of arterial puncture if the vein is transfixed. They also describe differences in anatomy between the two sides of the neck, complementing other studies that describe common anatomical variability of the neck vessels.
Ultrasound-guided infraclavicular axillary (or subclavian) vein access as opposed to landmark-based subclavian vein access is gaining in popularity. Indeed, in contrast to internal jugular venous access, it is recommended in many hospital guidelines as the route of choice if reduction of catheter-related blood stream infections is to be achieved. One example of this is the Matching Michigan patient safety initiative underway within the UK National Health Service. In this issue, a paper by Kim et al. 9 describes the depth and diameter of, and clinical approaches to the axillary vein when examined using ultrasound. Their report supports previous observations10 and promotes real time visualisation of the needle to avoid complications. It may also further encourage the choice of ultrasound-guided infraclavicular axillary (or subclavian) vein access, hopefully leading to studies that will fully establish whether the incidence of catheter-related blood stream infections is reduced when ultrasound is used at this site.
It is vital that adequate training in ultrasound-guided CVC access is provided. Continuing unintended arterial punctures suggest poor anatomical knowledge and technique, a view supported by a recent model-system study that demonstrated an unrecognised carotid artery puncture rate of 34%.11 Because this was a small study of US Emergency Medicine doctors, correlation to European models of anaesthesia training may not be absolute. However, it seems possible that when using ultrasound, the incidence of unrecognised arterial puncture may be higher than previously thought and occurs as the vein is transfixed with the artery lying behind. Training to ensure that operators achieve an optimal ultrasound image, the correct needle trajectory, and a non-transfixion technique should eliminate inadvertent arterial puncture. The development of formalised training programmes is in its infancy and there is currently no consensus on how training should be delivered, but an international consensus on the use of ultrasound is certainly a first step. Clearly, it should be part of speciality training for clinicians who regularly insert CVC; however, the requirements for clinicians who rarely perform such technique are uncertain. Related experience with ultrasound-guided interventions at other anatomical sites may significantly speed the acquisition of new skills. Further development of training models should aid the provision of safe training environments.
During the development of ultrasound-guided access, clinicians expressed reservations that a generation of doctors would emerge who would be unable to use a landmark technique and would not be competent to insert CVC in acute situations should ultrasound be unavailable or impractical. Recently, Harber et al. 12 have comprehensively demonstrated that anaesthetists who have trained in the ‘post-ultrasound era’ are unable to identify the IJV by the landmark technique. This is not surprising, but is it worrying?
When a new, safer method is introduced, the skills needed for the older technique will be lost. However, landmark techniques are not entirely redundant and there are limited situations in which there is a need to site CVC when ultrasound is unusable (e.g. widespread subcutaneous emphysema) or unavailable. For example, the British military, when resuscitating battlefield casualties prior to evacuation, may use a wide bore cannula inserted into the subclavian vein using a landmark technique. Other areas of military medical expertise have recently transferred to civilian practice13 and similar techniques of vascular access may well be employed within pre-hospital care.
How do we to train junior doctors in a technique which is less safe, infrequently practised, and will be unnecessary for the majority of trainees? One solution is to abandon the landmark technique completely and Ridley14 suggests a possible alternative algorithm. A different approach may be to provide training in the ultrasound technique and then superimpose the landmark technique for the few clinicians who require it, a reversal of the previous situation.
Technology also has a part to play in improving safety. Improving ultrasound equipment means that clinicians will increasingly be able to see smaller structures, such as smaller arterial branches, nerves, and the pleura, which may be subject to collateral damage. The widespread use of ultrasound machines with colour flow Doppler will aid the correct identification of vessels. There are still issues with poor needle visualisation, and technical developments such as compound imaging that affords simultaneous high-resolution views of the needle and the target should improve safety.
Ultrasound-guided central venous access is now an established technique and should be part of core practice for all clinicians inserting CVCs. Complications, however, continue to occur. The combination of improved training, growing familiarity with ultrasound, broadening of the scope of use, and developments in technology should minimise procedural complications. There may be a role for the landmark technique to complement ultrasound-guided access in certain situations, but the indications and training requirements have yet to be fully determined.
R.O'L. and A.B. are employed by the Leeds Teaching Hospitals NHS Trust and completed the Commentary within the scope of their current employment; no further funding was sought or obtained. Neither author has any conflict of interest.
This article was checked and accepted by the Editors, but was not sent for external peer-review.
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