◊ BACKGROUND:
Despite the growing interest in the use of ultrasound (US) imaging to guide performance of regional anaesthetic procedures such as peripheral nerve blocks, controversy still exists as to whether US is superior to previously developed nerve localization techniques such as the use of a peripheral nerve stimulator (PNS). We sought to clarify this issue by performing a systematic review and meta-analysis of all randomized controlled trials that have compared these two methods of nerve localization.
◊ METHODS:
We searched Ovid MEDLINE, the Cochrane Central Register of Controlled Trials, and Google Scholar databases and also the reference lists of relevant publications for eligible studies. A total of 13 studies met our criteria and were included for analysis. Studies were rated for methodological quality by two reviewers. Data from these studies were abstracted and synthesized using a meta-analysis.
◊ RESULTS:
Blocks performed using US guidance were more likely to be successful [risk ratio (RR) for block failure 0.41, 95% confidence interval (CI) 0.26-0.66, P<0.001], took less time to perform (mean 1 min less to perform with US, 95% CI 0.4-1.7 min, P=0.003), had faster onset (29% shorter onset time, 95% CI 45-12%, P=0.001), and had longer duration (mean difference 25% longer, 95% CI 12-38%, P<0.001) than those performed with PNS guidance. US guidance also decreased the risk of vascular puncture during block performance (RR 0.16, 95% CI 0.05-0.47, P=0.001).
◊ CONCLUSIONS:
US improves efficacy of peripheral nerve block compared with techniques that utilize PNS for nerve localization. Larger studies are needed to determine whether or not the use of US can decrease the number of complications such as nerve injury or systemic local anaesthetic toxicity.
◊ Reviewed by A. Borgeat, MD, PhD
Professor, chief of the department,
Dept. of Anesthesiology, Orthopedic University Hospital Balgrist, Zurich, Switzerland
Abrahams et al (1) performed a systematic review and meta-analysis of randomized controlled trials using guidance from ultrasound versus electrical stimulation for peripheral nerve blocks. The authors have to be commended for having undertaken such a task. This topic is of great interest and attempts to compare both techniques have been, still are, and probably will continue to be subject of controversy.
Abrahams et al found that US improves efficacy of peripheral nerve blocks compared with techniques using PNS for nerve localization. They did not find evidence that US decreases the number of nerve injury or systemic local anesthetic toxicity. However, before drawing any definite conclusions, it is imperative to highlight major weaknesses and limitations of this review in order to avoid further confusion on this controversial topic.
The main criticism refers to how the authors rated the analysed publications. They only assessed usual parameters like randomization, inclusion criteria etc., instead of using other validated systems were used (2,3) . The latter would have allowed to detect the methodological bias encountered in the vast majority of included investigations. For instance, NS requires a standardized stimulation current. Neuburger et al (4) have shown that thresholds down to 0.3 mA with an impulse duration of 0.1 ms are required to achieve a success rate of 95% in patients without polyneuropathy. Apart from the Casati study (5), no precisely fixed NS settings have been used. Inappropriate use of NS-guided blocks cannot furnish positive results. Kapral’s investigation (6) accepted finger flexion as endpoint for NS-guided interscalene block. This does not comply with common standards, and such a study should not be considered in any serious review or meta-analysis. Another example is the acceptance of the Perlas study (7) using inversion as an endpoint, which is well-known to be associated with a lower success rate (8,9). Such a study should not be included in a serious meta-analysis either. Finally, based on dubious power calculations, the great majority of these studies were underpowered (10-12). Unfortunately, this review was not able to identify and to control for confounders such as inexperienced use of neurostimulation, inappropriate block for a specific surgery, acceptance of inappropriate motor response, inadequate sample size etc.. This methodological bias compromises the validity of this analysis and raises serious doubts concerning the conclusions.
The potential of US-guidance in avoiding complications and improving success of regional blocks is appealing. However, there is still no evidence showing conclusive superiority of one technique over the other. Future trials must ensure that both techniques are performed according to best standards, since only under those conditions valid results and high level evidence can be obtained.
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