Abstract: Our systematic review included seven studies with a total of 492 participants. We included 422 participants in our analysis. Thirteen studies are awaiting classification. For the comparison dexmedetomidine versus placebo (six studies, 402 participants), most studies found a reduction in 'rescue' opioid consumption in the first 24 hours after surgery, together with in general no clinically important differences in postoperative pain (visual analogue scale (VAS) 0 to 100 mm, where 0 = no pain and 100 = worst imaginable pain) in the first 24 hours after surgery - except for one study (80 participants) with a reduction in VAS pain at two hours after surgery in favour of dexmedetomidine, with a mean difference of -30.00 mm (95% confidence interval (CI) -38.25 to -21.75). As the result of substantial heterogeneity, pooling of data in statistical meta-analyses was not appropriate. The quality of evidence was very low for our primary outcomes because of imprecision of results and risk of bias. Regarding our secondary aims, evidence was too scant in general to allow robust conclusions, or the estimates too imprecise or of poor methodological quality. Regarding adverse effects, low quality data (one study, 80 participants) suggest that the proportion of participants with hypotension requiring intervention was slightly higher in the high-dose dexmedetomidine group with a risk ratio of 2.50 (95% CI 0.94 to 6.66), but lower doses of dexmedetomidine led to no differences compared with control. Evidence for the comparison dexmedetomidine versus fentanyl was insufficient to permit robust conclusions (one study, 20 participants). Dexmedetomidine, when administered perioperatively for acute pain after abdominal surgery in adults, seemed to have some opioid-sparing effect together with in general no important differences in postoperative pain when compared with placebo. However the quality of the evidence was very low as the result of imprecision, methodological limitations and substantial heterogeneity among the seven included studies. The clinical importance for patients is uncertain, in as much as the influence of dexmedetomidine on patient-important outcomes such as gastrointestinal function, mobilization and adverse effects could not be satisfactorily determined. All included studies were relatively small, and publication bias could not be ruled out. Applicability of evidence was limited to middle-aged participants who were relatively free of co-morbidity and were undergoing elective abdominal surgery. A potential bias was a considerable quantity of unobtainable data from studies with mixed surgery. To detect and investigate patient-important outcomes, larger studies with longer periods of follow-up are needed.

Plain-language summary: Evidence is current to May 2014. We included seven studies with 492 participants from five different countries and included 422 participants in our analysis. Most participants were middle-aged. Participants had almost no diseases other than their reason for having surgery. The type of surgery was planned abdominal surgery. Three of the seven studies looked only at obesity surgery. Participants received dexmedetomidine right before or during their abdominal surgery. Six studies compared dexmedetomidine with no treatment, and one small study compared dexmedetomidine with fentanyl (a strong opioid). We reran the search in May 2015 and found nine studies of interest, which we will discuss when we update the review. In total, 13 studies are awaiting classification. Most of the studies that compared dexmedetomidine with no treatment found that dexmedetomidine reduced the need for opioids for treating pain for 24 hours after surgery. During the same period, no important differences in pain were noted, except one study (80 participants) showed a reduction in intensity of pain at two hours after surgery with dexmedetomidine. The quality of the evidence was very low because the results were not similar across studies, and because some studies were poorly conducted. The influence of dexmedetomidine on postoperative nausea and vomiting could not be determined because results were not similar across studies. No conclusion could be made for bowel function and mobilization and side effects such as postoperative sedation, as data were insufficient. One study with 80 participants reported a higher rate of low blood pressure ('low' meaning that medication was required) for participants receiving a high dose of dexmedetomidine compared with no treatment, but for lower doses of dexmedetomidine, they noted no differences compared with no treatment. For the comparison dexmedetomidine versus fentanyl, data were insufficient to allow conclusions (only one small study). Dexmedetomidine - compared with no treatment - seemed to reduce the need for opioids without worsening the experience of postoperative pain after abdominal surgery in adults. However, the quality of evidence was very low because studies were poorly conducted and because results were not similar across studies. The importance of these findings for patients was also uncertain because the influence of dexmedetomidine on bowel function, mobilization and adverse effects could not be properly determined.The seven included studies were small, so side effects associated with use of dexmedetomidine may be greater than this review reported. In addition, we could not obtain relevant data from several studies because investigators mixed abdominal surgery with other types of surgery.