Have advances in ultrasound technology improved our understanding and delivery of ra for shoulder surgery?

Abstract

Introduction: In this lecture, I would like to consider the development of 'handheld' ultrasound technology and its effect on the delivery of regional anaesthesia for shoulder surgery. Since handheld ultrasound imaging was introduced into mainstream clinical practice over ten years ago, we have witnessed worldwide a new 'golden age' of enthusiasm for regional anaesthesia using these techniques. This has manifested both clinically and in research output. The first handheld devices delivered inferior image quality when compared to the mainstream larger ultrasound machines, and this meant that we could only visualise the larger nerves with confidence. Researchers soon demonstrated that the brachial plexus could be easily visualised using ultrasound1. Interscalene brachial plexus blocks provide effective analgesia following shoulder surgery2, when applied as a single shot or continuous infusion3. Indeed, continuous infusions may improve outcome and shorten discharge times following major shoulder surgery4-7. The question researchers started to investigate was whether the use of ultrasound could improve the delivery of these successful techniques. Descriptions were soon published describing imaging of the brachial plexus in the interscalene groove and subsequent placement of effective blocks under ultrasound-guidance. This was achieved by direct visualisation of the neural structures, needle insertion and subsequent local anaesthetic spread in real-time, when placing blocks for shoulder surgery8. Anaesthetists also soon recognised the utility of ultrasound in situations where nerve stimulation may not be suitable or provide the feedback required on nerve proximity9-11 Success: The question of whether ultrasound makes us more successful when placing local anaesthetic blocks is controversial12. Kapral, who was one of the early pioneers of ultrasound-guided techniques, suggested that it does. He recruited 160 patients scheduled for trauma-related upper limb surgery. He then assessed the success rates of surgical anaesthesia following interscalene brachial plexus blockade. He found significantly improved rates of 99% and 91% respectively, using ultrasound-guidance and peripheral nerve stimulation for placement13; although the motor response end-point used in this study was subsequently questioned as too distal14. Other workers have also demonstrated high success rates for ultrasound-guided interscalene block, for example Davies et al. reported 99% in a series of 200 blocks15. We must interpret these types of findings (usually reported by experts in using ultrasound) in the knowledge that interscalene blocks placed using anatomical landmarks and nerve stimulation as an end-point can reach success rates of 97% in expert hands16. We also have indirect evidence for improved accuracy when using ultrasound-guidance. There is little argument that ultrasound improves accuracy of needle tip placement when compared to a landmark technique17, 18. When placing interscalene blocks, Sinha noted that accurate placement of a stimulating needle into the interscalene groove using ultrasound-guidance in 61 patients scheduled for ambulatory shoulder surgery resulting in complete sensorimotor block in all patients, resulted in a stimulating threshold range of 0.14 - 1.7 mA, with a current (less-than or equal to) 0.5 mA in only 42% of patients. Success is operator dependent; and other workers using ultrasoundguidance have shown reduced needle passes but no differences in success rates or complications when placing interscalene blocks19. However, I believe Liu's findings actually demonstrate an important difference between the nerve stimulation and ultrasound-guided techniques. The number of needle passes was significantly lower using ultrasound. This demonstrates that we can now directly visualise target structures and are usually able to relatively painlessly (i.e. without stimulation) approach those structures efficiently and accurately (using less needle passes) in order to place our local anaesthetic.We can also do this in patients with difficult anatomy or in whom we may not be able to elicit a motor response either due to disease, age of the patient, trauma or because they already have had local anaesthetic deposited around their nerves9-11. Volume: Ultrasound-guidance has allowed regional anaesthetists to use lower volumes of local anaesthetic. There is evidence that we can successfully use lower volumes compared to other techniques during peripheral nerve blockade20-24, 25. This evidence is a reflection of the improved accuracy available to regional anaesthetists when using ultrasound-guidance. This provides real advantages in terms of safety (reduced volume) and efficacy (improved accuracy). Safety: There is very little evidence regarding the relative safety of ultrasound-guidance compared to traditional nerve location techniques, nor is there likely to be; as the rates of complications due to the performance of regional anaesthesia are so low that demonstrating statistical differences between techniques is extremely problematic. One would assume that ultrasound should make the delivery of regional anaesthesia safer, as we are guiding the needle to the target and injecting local anaesthetic under direct vision. Indeed, ultrasound is extremely sensitive for detecting intraneural injection26, 27 and can also detect intravascular injection of local anaesthetic28, 29.