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Ultrasound ensures greater accuracy of local anaesthetic techniques

Simon Hebard and Harry Akerman
17 June, 2011  

Dr Simon Hebard
Specialist Registrar in Anaesthesia and Critical Care, Wessex Deanery, UK

Dr Harry Akerman
Consultant Anaesthetist, Southampton University Hospitals Trust, UK

Ultrasound imaging offers the anaesthetist an invaluable window into the anatomy of each individual patient. As in radiology, ultrasound in anaesthesia can be applied as both a diagnostic tool (echocardiography, thoracic/abdominal scanning) and, increasingly, a guidance tool for practical procedures (nerve blocks, arterial and venous access and so on).

In such a practical specialty, where virtually every procedure involves passing a needle into the human body, this technology can prove invaluable. Ultrasound visualisation of both the needle and the tissues beneath the patient’s skin can literally ‘open the eyes’ of a clinician where they would previously have been blind. Here we will focus on its potential in the field of regional anaesthesia – ultrasound-guided regional anaesthesia (UGRA).

Regional anaesthesia involves the injection of local anaesthetic around specific nerves to provide either anaesthesia or postoperative pain relief for patients. These ‘nerve blocks’ result in numbing the region of the body supplied by the nerve(s). The duration of block depends both on the choice of local anaesthetic and on whether or not a catheter is left in situ, allowing a continuous infusion of the local anaesthetic.

Regional anaesthesia can be used in place of general anaesthesia for many operations, facilitating so-called ‘awake surgery’. Such an approach can be used not only to reduce peri-operative risk in frail patients, but also to facilitate earlier discharge following elective surgery.1 In combination with a general anaesthetic, regional nerve blocks provide superior analgesia when compared to systemic opioids (e.g. morphine) with fewer side-effects.2 This again has been shown to reduce overall length of hospital stay.3-5

The situation before ultrasound-guidance
Regional anaesthesia has been practised successfully for decades, providing anaesthesia and pain relief for an untold number of patients. It would be fair to say, however, that mastery of the technique has proved somewhat elusive for the majority of anaesthetists. Successful location of the appropriate nerves relies upon a detailed knowledge of the ‘normal’ human anatomy, surface anatomical landmarks, the ‘feel’ as the needle passed through different tissues and the use of one of two nerve location methods. These methods comprise either the patient’s sensation of ‘pins and needles’ (parasthesia) as the needle touches the nerve or the application of an electric current via the needle to stimulate the desired nerve and observing for a characteristic muscle ‘twitch’ – peripheral nerve stimulation (PNS). Neither technique is ideal, but, to those who master them, both can be effective (>95% success rate).6

Importantly, neither of these nerve location methods can reliably detect needle-to-nerve contact (38% and 75% sensitive respectively).7 Nor can they give any indication of how the local anaesthetic is spreading in relation to the nerve. Advocates of general anaesthesia have sited its 100% success rate – fast onset and low risk of complications – when comparing it with regional techniques. But, in experienced hands, regional anaesthesia already provides most of these same attributes with the addition of an enhanced postoperative recovery profile.

What has ultrasound added?
The advent of affordable, portable, high-resolution ultrasound imaging equipment has enabled the anaesthetist both to visualise the deposition of local anaesthetic around target nerves and also to avoid needle contact with other vital structures, such as lung and blood vessels. The literature is expanding at pace, with initial small-scale, expert studies making way for larger, more robust research work. Evidence already exists for improved success rate (99%),8 reduced procedure time,9 reduced onset time and increased duration of block.8

No two patients are identical, so the flexibility to tailor one’s approach at an individual level rather than relying on generic surface landmarks is invaluable. Visualising the pattern of local anaesthetic spread gives previously unobtainable information as to the likely success and any potential complications of a given procedure (Figure 1).

We no longer need to make needle contact with the target nerve (parasthesia technique), with the associated risk of nerve damage, or attempt to produce muscle twitches (PNS), with potential discomfort for the patient. As a result of the above, the UK’s National Institute for Health and Clinical Excellence (NICE) has recently published its support for the use of ultrasound in regional anaesthesia (www.nice.org.uk/guidance).

What does this offer our patients?
In a nutshell, ultrasound is making regional anaesthesia more reliable and more accessible to the patient. Nerve blocks can be achieved more effectively. For those patients deemed unfit to undergo general anaesthesia, UGRA can often facilitate surgery that would otherwise have been impossible.

For those deemed fit, it again offers the option of undergoing their operation awake or otherwise the benefit of improved analgesia when they regain consciousness. Either of these approaches has been shown to enable patients to return home sooner. Nerve blocks performed under ultrasound have been shown to be quicker and involve fewer needle passes,9 with resultant benefits in terms of reduced patient discomfort. A faster onset and more reliable block has the potential to reduce patient anxiety and hence the need for sedation or general anaesthesia. Through advantages of UGRA in terms of theatre/ward efficiency (see below), more patients could potentially receive their operations sooner.

Ultrasound-guided regional anaesthesia is certainly no more risky than traditional non-ultrasound-based techniques and, ultimately, we anticipate that evidence will emerge for a superior safety profile. We already know that accidental damage to blood vessels9 and unwanted blockade of nearby nerves can be reduced.10

Lower doses of local anaesthetic can be used, thus reducing the risk of side-effects.11 Given the low incidence of prolonged nerve injury due to regional anaesthesia (1.6:10,000),12 large-scale studies will be needed to look at this specific complication. As with the introduction of any new technique, many anaesthetists are still on a steep learning curve and, as a result, it will be some time before the true benefits of UGRA become apparent.13

Health economics
With financial costs in healthcare ever increasing, efficiency and innovation with regards the processes involved are vital. Anaesthetists are ideally placed within the theatre environment to facilitate such changes, both through their clinical and their administrative skills. Regional anaesthesia has already proved an effective tool in our armoury, either as part of the package of care in innovative ‘enhanced recovery programmes’ shown to reduce length of hospital stay,5 or as a sole technique to facilitate awake surgery.1

The later approach can prove particularly effective, with its implementation on a single weekly orthopaedic theatre list in our institution, resulting in a reduction in overnight admission rates from 50% to 24% (upper limb surgery, unpublished data). This increase in day-case rate represents a cost saving of at least £15,000 per annum to the trust for just this list. Ultrasound is rapidly expanding the application of regional anaesthesia, both in terms of the number of anaesthetists competent to provide it and also the breadth of techniques available.

Future innovation
A new generation of ‘echogenic’ needles is emerging, with the intention of improving needle visibility under ultrasound with potential efficacy and safety benefits (Figure 2). Ultrasound imaging technology is constantly advancing and the competition between suppliers is fierce. This has resulted in improved imaging being available at far less expense. Three- and even four-dimensional ultrasound technology already exists, although its utility in the field of regional anaesthesia has yet to be well defined. Pharmacological research is ongoing into longer-acting local anaesthetic drugs, with the aim of increasing the duration of pain relief obtainable from a single injection.

UGRA has the potential to make the established benefits of regional anaesthesia a reality for a far greater proportion of the patient population. This is primarily due to its improved efficacy, efficiency and flexibility when compared with traditional nerve location techniques. Definitive data on safety benefits are eagerly awaited.

References

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  2. 
Mathur V et al. Techniques in Regional Anesthesia and Pain Management 2008;12:
163-170.
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Wang H et al. Reg Anesth Pain Med 
2002;27:139-44.
  4. Capdevila X et al. Anesthesiology 1999;91:8-15.
  5. Basse L et al. Ann Surg 2000;232:51-7.
  6. Perris TM et al. Anaesthesia 2003;58:1220-4.
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Perlas A et al. Reg Anesth Pain Med 
2006;31:445-50.
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Kapral S et al. Reg Anesth Pain Med 
2008;33:253-8.
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Orebaugh SL et al. Reg Anesth Pain Med 2007;32:448-54.
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Renes SH et al. Reg Anesth Pain Med 2009;34:498-502.
  11. 
Casati A et al. Anesthesiology 2007;106:992-6.
  12. 
Auroy Y et al. Anesthesiology 2002;97:1274-80.
  13. 
Sites BD et al. Reg Anesth Pain Med 
2004;29:544-8.