Cross-over trials are typically more efficient than parallel group trials in that the sample size required to yield a desired power is substantially smaller. It is important, however, to consider some issues specific to cross-over trials when designing and reporting them, and when evaluating the published results of such trials. This systematic review evaluated the quality of reporting and its evolution over time in articles of cross-over clinical trials of pharmacologic treatments for chronic pain published between 1993 and 2013. Seventy-six (61%) articles reported a within-subject primary analysis, or if no primary analysis was identified, reported at least 1 within-subject analysis, which is required to achieve the gain in power associated with the cross-over design. For 39 (31%) articles, it was unclear whether analyses conducted were within-subject or between-group. Only 36 (29%) articles reported a method to accommodate missing data (eg, last observation carried forward, n = 29), and of those, just 14 included subjects in the analysis who provided data from only 1 period. Of the articles that identified a within-subject primary analysis, 21 (51%) provided sufficient information for the results to be included in a meta-analysis (ie, estimates of the within-subject treatment effect and variability). These results and others presented in this article demonstrate deficiencies in reporting of cross-over trials for analgesic treatments. Clearer reporting in future trials could improve readers' ability to critically evaluate the results, use these data in meta-analyses, and plan future trials. Recommendations for proper reporting of cross-over trials that apply to any condition are provided.

The use of transversus abdominis plane (TAP) block to provide either analgesia or anesthesia to the anterior abdominal wall is well described. The technique yields high analgesic effectiveness and is opioid sparing and potentially of long duration with reported analgesia lasting up to 36 hours. When compared to neuraxial analgesia, TAP blocks are associated with a lower incidence of hypotension and motor blockade. TAP blocks are typically described as providing somatic analgesia only without any effect on visceral pain. There may be, however, certain conditions in which TAP blocks can provide effective analgesia in pain of visceral or mixed somatic and visceral origin. We describe two cases in which TAP blockade provided complete control of pain considered to be of visceral origin.

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