“…[8][9][10][11][12][13][14][15] However, there is considerable variation between studies in terms of dose of opioid, pain measures used, and risk of bias associated with published trials, making it difficult for practitioners to derive clinically useful information from the results. Thus, there is considerable variation in practice in terms of use of background infusion, as well as dose, duration, and type of operation for which a concurrent background IV infusion might be used.…”