THE modern era of regional anesthesia began with a simple needle. Some pioneers believed it was not necessary to have an open surgical field to perform regional blocks; indeed, they were able to demonstrate that it was possible to successfully achieve regional blocks by inserting a needle transcutaneously and searching for paresthesias.1Despite positive results, this technique had some major drawbacks, including active patient participation and elicitation of a paresthesia, a sensation that was later shown to be the most unpleasant part of the regional block procedure.2Science was injected into the art of regional anesthesia with the advent of neurostimulation. With the development of more reliable equipment and introduction of safer and more effective local anesthetics, needle guidance by neurostimulation enhanced the safety and efficacy of regional anesthesia.3,4More recently, a new method of performing regional block using ultrasound technology has been introduced in clinical practice. Whether ultrasound offers significant advantages over other aids to regional anesthesia represents a central issue in clinical research in the field. In this issue of Anesthesiology, Casati et al. 5make a substantial contribution to this question, demonstrating that in experienced hands, neurostimulation and ultrasonography have similar success rates and comparable incidences of complications after multiple injection axillary brachial plexus block. Moreover, patient satisfaction was similarly good with both techniques.
The authors investigated the challenging question of whether neurostimulation or ultrasonography will selectively affect success rate, incidence of complications, and patient acceptance after multiple injection axillary brachial plexus block. Axillary brachial plexus block was a good choice for such a study because this block is considered as one of the most unpleasant when performed with the use of neurostimulation.2This reflects the need at this site to perform three separate stimulations/injections to obtain a high success rate.6,7The results obtained by Casati et al. 5will not surprise experts in regional anesthesia, who most likely would have predicted no difference between the two techniques in these clinically relevant outcomes, when the blocks are performed by experienced anesthesiologists. Recent progress in the science and application of neurostimulation to localize peripheral nerves has been rapid in many areas. Johnson et al. ,8for example, applied a computerized model of electrical stimulation of peripheral nerves and contributed new and unexpected important observations with direct clinical application. The increased sophistication of the application of neurostimulation, the availability of bevelled insulated needles, and the description of new approaches have made neurostimulation a highly successful technique in experienced hands (up to 95–97%4,9,10), associated with a low incidence of severe complications.
One of the most relevant issues would be to know whether ultrasound can still increase the high success rate observed with neurostimulation. In fact, observations in cadaver dissections or direct visualization during surgery indicate cases of a thick perineurium or a complex network of connective tissue between the cords at the infraclavicular level, for example. These anatomical variants may explain why a 100% success rate within 30 min will never occur, whatever technique is used. These considerations help to understand why a significant difference between the two techniques regarding success rate will most likely never be demonstrated because the required number of patients to show even a small difference will be tremendously large.
Another important question is to know whether ultrasound would decrease the incidence of the most feared complication—neuropathy—which occurs nevertheless in 0.04–0.4%3,4,10,11with the use of neurostimulation. This low incidence of neuropathy in literature reports almost certainly includes some injuries due to surgery and suggests that some injuries in large surveys will always be observed. Given the extremely low incidence of serious neuropathy and its mixed causes, attempting to determine whether one technique to localize nerves for regional anesthesia is safer than another in regard to neuropathy would be a huge undertaking, requiring tens of thousands of patients to observe even small difference between techniques. Such studies will most likely never be performed. On the other hand, it is conceivable that visualization with ultrasound may further our understanding of the mechanisms of neuropathy after regional anesthesia. For example, Bigeleisen12performed axillary plexus blocks with his usual practice of seeking a paresthesia by needle manipulation. When a paresthesia was obtained, he assessed the spread of local anesthetic solution using ultrasound. His observations were astonishing: 85% of the patients had nerve puncture of at least one nerve, and 81% had an intraneural injection of at least one nerve.12Surprisingly, 6 months later, no neural damage was noted. This study suggests that injection through the epineurium is common with the use of the paresthesia technique and that some local anesthetics may be injected between the perineurium and epineurium without damaging the nerve.
Supporters of the ultrasound technique will point out that in Casati’s study, minor outcomes such as onset of sensory block or number of needle passes favored the ultrasound method over neurostimulation. Supporters of the neurostimulation technique will counter that only three stimulations are really required, rather than four,7making the procedure less unpleasant than in Casati’s study, and that thinner needles than used in this study may be used and would further reduce patient discomfort. Regardless, patient acceptance was similar with these methods, and perhaps the important point is not to contrast these conceptually different methods13—neurostimulation, an analytic tridimensional technique, and ultrasonography, a descriptive bidimensional one—but rather to understand that combining the two may help to improve our understanding regarding the interactions between the distance between needle and nerve as it relates to muscle response and spread of local anesthetic solution. The dynamic visualization of regional anesthesia will undoubtedly contribute to further refine the scientific basis of regional anesthesia.
Should one technique be chosen over the other? Casati et al. 5clearly demonstrated that in experienced hands, the major outcomes for performing a single-shot nerve block are similar between the two techniques. Individual practitioners may certainly have different success rates and hence preferences for one technique over another.
Finally, whether these results inform us regarding continuous perineural catheter techniques is worth a comment. Single-shot regional anesthesia does not significantly alter clinical outcomes compared with general anesthesia. McCartney et al. ,14for example, demonstrated that pain severity, morphine consumption, and incidence of nausea and vomiting were similar after ambulatory hand surgery between single-shot peripheral nerve block and general anesthesia. On the contrary, continuous local anesthetic infusion by perineural catheters has significantly improved outcome.15–18Its placement with the use of neurostimulation is well standardized,19,20the search for specific muscle response is well defined,3,9,21and the incidence of infection, a crucial issue in this context, is low.3,4Some of these concerns, particularly the issue of sterility, must be further investigated regarding ultrasound-guided perineural catheters. In any case, as written by J. Giraudoux, the Trojan War will not take place.22
* Department of Anesthesiology, Orthopedic University Clinic Balgrist, Zurich, Switzerland. firstname.lastname@example.org. † Department of Anesthesiology, Centre Hospitalier Universitaire de Montpellier, Montpellier, France.