Editorial I: Location, location, location! Ultrasound imaging in regional anaesthesia

N. M. Denny*

Department of Anaesthesia, Queen Elizabeth Hospital, King's Lynn, Norfolk PE30 4ET, UK

W. Harrop-Griffiths

Department of Anaesthesia St Mary's Hospital, Praed Street London W2 1NY UK

* Corresponding author. E-mail: nicholas.denny{at}btinternet.com

Regional anaesthesia always works—provided you put the right dose of the right drug in the right place (M. Morgan, personal communication). When it does not work, it is usually because the local anaesthetic has not been put in the right place. The three primary keys to successful regional anaesthesia are therefore nerve location, nerve location and nerve location. This issue contains a review by Marhofer and colleagues1 that summarizes the first 10 yr of the use of ultrasound to identify nerves, to visualize the passage of a needle towards the nerve, and to monitor the distribution of local anaesthetic during injection. It is an interesting and thought-provoking article that unreservedly praises the technique and ascribes it an ‘almost 100%’ success rate. Unreserved praise and claims of 100% success rates always draw cynicism from anaesthetists—even more so from hard-bitten regional anaesthetists who live daily with the risk of technique failure. We will therefore take a step back and try to set the use of ultrasound into context.

The first brachial plexus block was performed under direct vision.2 After surgical exposure, the plexus was bathed with cocaine. In spite of what was almost certainly a 100% success rate, this approach was, quite reasonably, abandoned in favour of the percutaneous injection of local anaesthetic through a needle. In the middle of the 20th century, some 50 yr after the first use of local anaesthesia, anaesthetists were still dependent on a detailed knowledge of anatomy, the sensation of the passage of a needle through tissue planes, and the provocation of paraesthesiae in awake patients to confirm the correct placement of the block needle. Even so, high success rates were possible, although these were largely the preserve of experts. By the latter part of the 20th century, the development of electrical nerve stimulation to locate peripheral nerves led to a vigorous debate about its role in regional anaesthesia. ‘No paresthesias, no anesthesia!’ chanted Danny Moore.3 ‘No paresthesiae, no dysaesthesia!’ retorted the supporters of nerve stimulation.4 After more than 25 yr of nerve stimulator use, there is still no consensus as to whether it is an easier, safer or more effective technique than using paraesthesiae to locate nerves, in spite of a large number of published studies. As recently as 2001, debate raged on the subject of paraesthesiae versus electrical nerve stimulation,5 and yet the large majority of regional anaesthetists in the developed world now use electrical nerve stimulation.

What is the standard of evidence that would be required for regional anaesthetists to convert from nerve stimulation to ultrasound as their preferred technique? Convincing demonstrations that the use of ultrasound leads to a faster onset of block and lower local anaesthetic doses should be relatively easy to provide, and yet these may not be the primary determining factors in regional anaesthetists' choice of technique. With success rates above 95% for peripheral nerve blocks when performed by experienced anaesthetists, it will require large studies to prove that ultrasound-guided blocks have a consistently higher success rate. What about safety—the factor that should influence anaesthetists the most in their choice of technique? Let us take Marhofer's contention that one of the ‘potential advantages of ultrasound guidance compared with conventional techniques of nerve identification’ is avoidance of side-effects.1 He quotes nine published studies to support this contention.614Seven are from his own group; four are descriptive and do not compare ultrasound with another technique; and only three of the five comparative studies compare ultrasound with electrical nerve stimulation. A total of 140 patients were investigated in these three studies. In these 140 patients, only five complications were recorded: all were arterial punctures that produced small haematomas but no other untoward effects. These data cannot be taken as proof that the use of ultrasound is safer than electrical nerve stimulation. However, this statement does not imply that ultrasound is not safer than electrical nerve stimulation, simply that it has not yet been proved; indeed, it may be very difficult to prove. When comparing ultrasound with nerve stimulation, it is impossible to blind the technique to the operator; bias is inevitable and understandable. The incidence of permanent neurological damage after peripheral nerve block (arguably the regional anaesthetist's most feared complication) has been quoted to be in the order of 1:5000 to 1:10 000.15 16 The studies that would be needed to show a significant difference in terms of safety would not just be large, they would be huge. We must prepare ourselves for the likelihood that these studies, if they are ever performed, will probably appear in the literature long after the regional anaesthetic community has already made its choice between nerve stimulation and ultrasound.

We must all do our best to practise evidence-based medicine, but we must also accept that in the absence of evidence, or in the presence of evidence that cannot convince, doctors must rely upon the evidence that is their own personal experience. While regional anaesthesia research groups perform studies that may (or may not) show that one technique is (or is not) slightly superior to another, practising regional anaesthetists will acquire ultrasound machines and will use them to perform blocks. If their experiences are positive, a silent revolution will occur, and just as peripheral nerve stimulation took over from paraesthesiae towards the end of the 20th century in the absence of clear guiding evidence, the use of ultrasound may take over from peripheral nerve stimulation at the beginning of this century. Change, if it happens, will be in the hands of the clinicians, not the researchers.

Evidence aside, it is intuitively better and safer to perform a procedure under direct vision than blind, albeit with the limited assistance that is provided by muscle contractions evoked by nerve stimulation. Ultrasound is a big step towards direct visualization, and yet it is not direct visualization. Two-dimensional pictures from the ultrasound monitor screen that have been published usually fail to impress. The bundles of nerves displayed more resemble the vague speckled pattern of a thrush's breast than a detailed neuroanatomical cross-section. However, the clinical use of ultrasound is more four-dimensional than two-dimensional. A series of two-dimensional images produced by a slowly moving probe can be reconstructed in the mind of the anatomical savant to produce a three-dimensional map of the area. With manual dexterity, the operator can then direct the needle towards the target nerve. The additional (fourth) dimension of time allows the operator to assess the spread of the local anaesthetic during injection.

It is this need for three-dimensional spatial awareness and anatomical knowledge that concerns regional anaesthetists, who are firmly of the opinion that there are far too few regional anaesthesia practitioners and teachers, and that this may, in part, be a result of the above prerequisites. If ultrasound nerve location makes regional anaesthesia quicker, more effective and safer, it will be adopted by regional anaesthetists. If it also makes it easier, more anaesthetists will be drawn towards regional anaesthesia. However, one concern is that the successful use of ultrasound may demand more training, a more detailed knowledge of anatomy, and even greater manual dexterity, and that regional anaesthesia will therefore continue to be the preserve of the committed few. To use one of Alon Winnie's best aphorisms: ‘When there are problems with any regional technique, look for the cause first on the proximal end of the needle’.17 It is the knowledge, experience and skill of the operator that determine the outcome, and it is possible that those who use nerve stimulation safely and successfully will also be the ones who use ultrasound safely and successfully.

Ultrasound imaging is proving useful in the training of regional anaesthetists. The relevant anatomy can be demonstrated, and many of the structures that regional anaesthetists seek to avoid are clearly shown: the pleura, arteries and veins. It is for this reason that the availability of ultrasound may provoke a change in regional anaesthetic practice. Blocks of the brachial plexus around the clavicle, once popular because of their rapid onset, wide anatomical coverage and reliability, have decreased in popularity, in large part because of the fear of producing a pneumothorax. When the pleura can be visualized and therefore more easily avoided, these blocks may become popular once again, to the benefit of patients.

Ultrasound imaging will undoubtedly form an important and enduring part of training in regional anaesthesia. Will it become part of everyday clinical nerve blockade? The resounding answer from the authors of this editorial is: perhaps. Ultrasound enthusiasts will continue to claim that its use will produce faster, safer and more successful blocks. The cynics may well turn to analogy in their fight against progress: ultrasound machines may prove to be like in-car satellite navigation systems—invaluable if you are in unfamiliar territory, but next to useless if you know where you are going. Only time, and the hands-on experience of regional anaesthetists, will tell.

References

1 Marhofer P, Greher M, Kapral S. Ultrasound guidance in regional anaesthesia. Br J Anaesth 2005; 94: 7–17

2 Winnie AP. Historical considerations. In: Plexus Anesthesia, Perivascular Techniques of the Brachial Plexus. Philadelphia: W. B. Saunders, 1983; 68–9

3 Moore DC. ‘No paresthesias—no anesthesia’, the nerve stimulator or neither? Reg Anesth 1997; 22: 388–90[ISI][Medline]

4 Selander D, Edshage S, Wolff T. Paresthesiae or no paresthesiae? Acta Anaesthesiol Scand 1979: 23: 27–33[ISI][Medline]

5 American Society of Regional Anesthesia and Pain Medicine Newsletter, May 2001 http://www.asra.com/Newsletters/May_01.pdf

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7 Greher M, Retzl G, Niel P, Kamolz L, Marhofer P, Kapral S. Ultrasonographic assessment of topographic anatomy in volunteers suggests a modification of the infraclavicular vertical brachial plexus block. Br J Anaesth 2002; 88: 632–6[Abstract/Free Full Text]

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11 Marhofer P, Schrogendorfer K, Andel H, et al. Combined sciatic nerve—3 in 1 block in high risk patient. Anaesthesiol Intensivmed Notfallmed Schmerzther 1998; 33: 399–401

12 Marhofer P, Schrogendorfer K, Wallner T, Koinig H, Mayer N, Kapral S. Ultrasonographic guidance reduces the amount of local anesthetic for 3-in-1 blocks. Reg Anesth Pain Med 1998; 23: 584–8[CrossRef][ISI][Medline]

13 Marhofer P, Greher M, Sitzwohl C, Kapral S. Ultrasonographic guidance for infraclavicular plexus anaesthesia in children. Anaesthesia 2004; in press

14 Sandhu NS, Capal LM. Ultrasound-guided infraclavicular brachial plexus block. Br J Anaesth 2002; 89: 254–9[Abstract/Free Full Text]

15 Auroy Y, Narchi P, Messiah A, Litt L, Rouvier B, Samii K. Serious complications related to regional anesthesia: results of a prospective survey in France. Anesthesiology 1997; 87: 479–86[CrossRef][ISI][Medline]

16 Auroy Y, Benhamou D, Bargues L, et al. Major complications of regional anesthesia in France: The SOS Regional Anesthesia Hotline Service. Anesthesiology 2002; 97: 1274–80[CrossRef][ISI][Medline]

17 Winnie AP. Consideration concerning complication, side effects and untoward sequelae. In: Plexus Anesthesia, Perivascular Techniques of the Brachial Plexus. Philadelphia: W. B. Saunders, 1983; 221