Equivalence is victory.

Ultrasound (US) has revolutionized almost every medical discipline. The anesthesia community now uses US routinely in the form of transesophageal echocardiography, facilitation of vascular access, and guidance for regional anesthesia. Clearly, US-guided regional anesthesia (UGRA) has increased in popularity. This is evident by the popular expansion of workshops at the American Society of Regional Anesthesia meetings, a designated section of the journal Regional Anesthesia and Pain Medicine, the incorporation of UGRA curriculums in academic training programs, the committed UGRA chapter in Miller’s Anesthesia textbook, and the plethora of web-based resources. Despite its popular growth, the question remains whether US techniques are superior to traditional landmark techniques incorporating nerve stimulation (NS). The answer to this question depends on the outcome variable being studied as well as the individual definitions of success versus failure. For technical block-related outcomes such as performance time, block onset, local anesthetic dose, and sensory block quality, the literature overall supports the use of UGRA and demonstrates superiority over the traditional nerve localization techniques (i.e., nerve stimulation). However, US has received its share of criticism. It has been questioned whether these technical block-related outcomes are clinically meaningful. In other words, even if US allowed for the quicker placement of peripheral nerve blocks with a quicker onset time, does this prove overall superiority? Critics would answer “no,” because multiple controlled trials have failed to ultimately demonstrate a US-related reduction in the need for conversion to general anesthesia. Therefore, when a successful surgical block specifically defines the quality metric, US seems to represent a nonbeneficial additional cost in comparison with the use of NS. In this issue of Anesthesia & Analgesia, Choi and Brull have gone beyond looking at specific block-related outcomes. Rather, they evaluated meaningful outcomes as they relate to acute pain. Specifically, they provide us with a comprehensive review of the literature as it stands in 2011 comparing US with NS with the focus on acute painand pain-related outcomes. The acute pain-related outcomes reviewed include visual analog scale scores, time to first analgesic request, sensory block duration, opioid consumption, opioid-related side effects, patient satisfaction, complications, and length of hospital stay. Overall, for each of these outcome variables, they demonstrated that the literature either favored the use of US or was equivocal. Why is robust evidence supporting the use of US over traditional nerve localization techniques for acute painrelated outcomes lacking? The answer lies in how randomized controlled trials (RCTs) are designed and what the primary outcome variable is powered to detect. Of the 23 RCTs cited by Choi and Brull, there were only 8 studies in which the primary outcome variable was an acute painrelated outcome (pain, sensory block duration, or frequency of surgical block). In the other 15 studies, the primary outcomes measured were block-related such as sensory block, onset time, performance time, number of needle passes, and local anesthetic consumption. Therefore, the majority of the RCTs have not been powered to evaluate the outcomes that Choi and Brull set out to understand. Not surprisingly, they concluded that the current data are insufficient to form any meaningful conclusions. On the contrary, the situation is different for block-related outcome variables, whereby US clearly has demonstrated a distinct advantage over traditional nerve localizations. In our own independent appraisal of the literature, and the appraisal of others, we could only identify 1 RCT in which the primary outcome variable was powered to detect a difference in the quality of a surgical block (the conversion of a failed regional anesthetic to a general anesthetic). Future studies should be appropriately designed and powered to answer meaningful acute pain-related outcomes as well as block-related outcomes such as the conversion of regional anesthesia to general anesthesia. We strongly believe that trying to evaluate US versus NS as it pertains to acute pain outcomes is fraught with inefficiencies and methodological flaws that do not justify the costs of performing such clinical research. The emphasis should remain on block-related outcomes such as performance time, patient tolerance, sensory block, and the quality of a surgical block. US is not a drug being added to a local anesthetic technique, but merely a guidance technology. Significant postoperative benefits, whether long-term or short-term, from a documented complete surgical block performed either by US or NS should be identical. Furthermore, even if there were subtle differences, no clinical trial would have sufficient power to tease them out. In fact, our research community has not even been able to definitively “prove” that regional From the *Department of Anesthesia, Portsmouth Anesthesia Associates, Portsmouth Regional Hospital, Portsmouth; and †Department of Anesthesia, Dartmouth Medical School, Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire.