Does ultrasound improve safety?
How has ultrasound guidance impacted the safety of peripheral nerve blockade?
The ability to visualize anatomy in real time at the bedside while performing peripheral nerve blocks has dramatically changed many practitioners’ perceptions of regional anesthesia. While knowledge of anatomy remains a cornerstone of regional anesthesia, with ultrasound guided regional anesthesia a practitioner may now image anatomy in real time, as well as plan the needle path, avoiding vulnerable structures and ensuring local anesthetic delivery close to the nerve. Furthermore, the needle tip may be kept in view at all times as it is advanced, and local anesthetic spread modified as necessary to ensure appropriate perineural spread.
This ability to directly image the process has resulted in some fairly predictable advantages of ultrasound use, which explain its ever-increasing popularity. These advantages include a higher block success rate when compared to nerve stimulation guidance, fewer needle passes with possibly less trauma, and a greater degree of sensory blockade.1-5 Other improvements include a more rapid block onset, more rapid block conduct, and a longer analgesic duration.1,5,6 These advantages have also translated into greater ease and success for peripheral catheter insertion.7
In the first five or so years of ultrasound use for peripheral nerve block guidance, there was considerable doubt regarding whether this imaging modality provided measurable practical benefit, or whether ultrasound guidance for peripheral block was an expensive extravagance. The studies and meta-analyses noted above have markedly strengthened the evidence in favor of ultrasound for peripheral nerve blocks. Other reports have made it clear that instructing residents is facilitated by use of ultrasound – in our own academic practice we have seen the frequency of inadequate or partial interscalene block drop from 11% to just over 2%.8 From a rotation director’s perspective, the advent of ultrasound guided blocks was a truly remarkable advance for resident instruction, while at the same time enhancing patient safety. Guidelines for regional anesthesia instruction now routinely incorporate ultrasonography.9
Unfortunately, the impact of ultrasound guidance for regional anesthesia on patient safety has not been demonstrated as clearly as its practical advantages. With regard to nerve injury, several large databases and some randomized trials have failed to show a difference between guidance techniques, in terms of significant nerve injury or more mild postoperative nerve dysfunction (i.e. numbness and tingling).3,10-12 This may be because the majority of such injuries are not block related,10 or because neural dysfunction, if block-related, is attributable to factors other than needle-tip trauma such as local anesthetic neurotoxicity. Given these issues and the very low frequency of serious nerve injury, it may not be possible to show a difference in postoperative neurologic outcomes with the use of ultrasound to guide needle placement and local anesthetic deposition.
The influence of ultrasound upon the other major adverse outcome from peripheral nerve block, local anesthetic systemic toxicity (LAST), has been more readily addressed in the literature. Two large databases provide evidence for a very low frequency of seizure or cardiac toxicity when ultrasound is used to guide nerve blocks. While prior estimates of LAST ranged from 1/1000 to 1/7000 when nerve stimulation was the primary method of guidance, Sites et al. 13 recently reported the experience at Dartmouth, where in a six-year period, over 12,000 ultrasound-guided blocks resulted in only one episode of LAST (a seizure). We also recently reported our six-year experience at University of Pittsburgh Medical Center-South Side.14 Our data are somewhat unique in that they reflect a multi-year transition from primary guidance by nerve stimulator, to almost complete use of ultrasound (over 90%), as well as that the vast majority of blocks being conducted by supervised residents. In some 6,000 nerve stimulator blocks, there were six seizures, while in the 9,000-plus blocks conducted with ultrasound guidance, there were no episodes of LAST. Temporally, there was a clear correlation between the use of ultrasound and reduced risk of seizures. Finally, the most compelling data regarding improved safety comes from a multi-center Australia-New Zealand database recently reported as an abstract at the 2012 American Society of Anesthesiologists annual meeting. Barrington, et al.15 summarized their results with over 20,000 peripheral nerve blocks conducted with either ultrasound or nerve stimulator guidance. Both univariate and multivariate regression established ultrasound guidance as a factor which favorably influenced the occurrence of LAST, with an odds ratio between 0.18 and 0.25. The total dose of local anesthetic and dose per patient body weight were likewise correlated with toxicity risk.
Some reasons for ultrasound imaging favorably affecting LAST are obvious. There are fewer vascular needle punctures,1,2 primarily because vessels can be visualized. While this may only be a surrogate for intravascular injection, it probably plays a role. In addition, ultrasound has allowed a marked decrease in local anesthetic doses while still providing effective blocks,2,16,17 which inevitably impacts on safety. What is not so obvious, perhaps, is that for many blocks, use of the ultrasound transducer changes our trajectory of needle insertion: shallower, more oblique approaches are necessary to image the needle and to align the needle under the probe.18 Thus, we are less likely to plunge the needle deep beyond the nerve where sizable vessels may be inadvertently punctured and subjected to injection (for example, vertebral artery puncture during interscalene block).
In summary, ultrasound has clearly had a favorably influence upon the technical and practical aspects of peripheral nerve block performance, and its popularity continues to grow. Any effect on block-related nerve injury has been difficult to establish, but one promise of real-time ultrasound imaging for peripheral block is the ability to avoid inadvertent intravascular local anesthetic injection with possible severe toxicity. With ultrasound-guided regional anesthesia, patients are safer, and practitioners (and instructors) can proceed with greater confidence in integrating regional techniques into the anesthesia plan for their patients.
For practical advice on maximising ultrasound guided regional anesthesia safety, refer to the following pages:
1. MS, Aziz MF, Fu RF, Horn J-L. Ultrasound guidance compared with electrical neurostimulation for peripheral nerve block. Br J Anaesth 2009;102:408-417.
2. Marhofer P, Schrogendorfer K, Wallner T, Koinig H, Maryer N, Kapral S.guidance reduces the amount of local anesthetic for 3-in-1 blocks. Reg Anesth Pain Med 1998;23:584-588.
3. Chan VWS, Perlas A, McCartney CJ, Brull R, Xu D, Abbas D. Ultrasound guidance improves success rate of axillary brachial plexus block. Can J Anaesth 2007;54:5941-5947.
4. Kapral S, Greher M, Huber G, Willschke H, Kettner S, Dkolsky R, Marhofer P. Ultrasonographic guidance improves the success rate of interscalene brachial plexus blockade. Reg Anesth Pain Med 2008;33:253-258
5. Perlas A, Brull R, Chan VWS, McCartnery CJL, Nuica A, Abbas S. Ultrasound guidance improves the success of sciatic nerve block at the popliteal fossa. Reg Anesth Pain Med 2008;33:259-265.
6. Williams S, Chouinard P, Arcand G, Harris P, Ruel M, Boudreault D, Girard F. Ultrasound guidance speeds execution and improves the quality of supraclavicular block.
7. Mariano ER, Cheng GS, Choy LP, Loland VJ, Bellars RH, Sandhu NS, Bishop ML, Lee DK, Maldonado RC, Ilfeld BM. Electrical stimulation versus ultrasound guidance for popliteal-sciatic perineural catheter insertion. Reg Anesth Pain Med 2009;34:480-485.
8. Orebaugh SL, Williams BA, Kentor MK, Bolland MA, Mosier SK, Nowak TP. Interscalene block using ultrasound guidance: Impact of experience on resident performance. Acta Anaesth Scand 2009;53:1268-1274.
9. Sites BD, Chan VWS, Neal JM, Weller R, Grau T, Koscielniak-Nielse ZJ, Ivani G. The American Society of Regional Anesthesia and Pain Medicine and the European Society of Regional Anaesthesia and Pain Therapy Joint Committee Recommendations for Education and Training in Ultrasound-Guided Regional Anesthesia. Reg Anesth Pain Med 2010;35(Supplement 1):S74-S80.
10. Barrington MJ, Watts SA, Gledhill SR, Thomas RD, Said SA, Snyder GL, Tay VS, Jamrozik K. Reg Anesth Pain Med 2009;34:534-541.
11. Orebaugh SL, Williams BA, Kentor ML. Adverse outcomes associated with stimulator-based peripheral nerve blocks with versus without ultrasound guidance. Reg Anesth Pain Med 2009;34:251-255.
12. Liu SS, Zayas VM, Gordon MA, Beathe JC, Maalouf DB, Paroli L, Liguouri GA, Ortiz J, Buschiazzo V, Ngeow J, Shetty T, Ya Deau JT. A prospective, randomized controlled trial comparing ultrasound versus nerve stimulator guidance for interscalene block for ambulatory shoulder surgery for postoperative neurological symptoms. Anesth Analg 2009;109:265-271.
13. Sites BD, Taenzer AH, Herrick MD, Gilloon C, Antonakakis J, Richins J, Beach ML. Incidence of local anesthetic systemic toxicity and postoperative neurologic symptoms associated with 12,668 ultrasound-guided nerve blocks. Reg Anesth Pain Med 2012;37:478-482.
14. Orebaugh SL, Kentor ML, Willams BA. Adverse outcomes associated with nerve stimulator-guided and ultrasound-guided peripheral nerve blocks by supervised trainees: Update of a single site database. Reg Anesth Pain Med 2012;37:577-582.
15. Barrington MJ, Kluger R. Use of ultrasound guidance for peripheral nerve blockade is associated with a reduced incidence of local anesthetic systemic toxicity. Abstract presented at American Society of Anesthesiologist annual meeting, Washington, DC, October 2012.
16. Casati A, Baciarello M, Di Cianni S, Danelli G, De Marco G, Leone S, Rossi M, Fanelli G. Effects of ultrasound guidance on the minimum effective anaesthetic volume required to block the femoral nerve. Br J Anaesth 2007;98:823-827.
17. Riazi S, Carmichael N, Awad I, Holtby RM, McCartney CJL. Effect of local anaesthetic volume on the efficacy and respiratory consequences of ultrasound-guided interscalene brachial plexus block. Br J Anaesth 2008;101:549-556.
18. Neal JM. Ultrasound-guided regional anesthesia and patient safety. Reg Anesth Pain Med 2010;35(Supplement 1):S59-S67.