The analgetic effect of adjuvants in local infiltration analgesia - a systematic review with network meta-analysis of randomized trials

BACKGROUND: Local infiltration analgesia is commonly used for postoperative pain control after several surgical procedures including intra- and peri-articular as well as wound infiltration. Even though, various adjuvants injected with the local anesthetic have been studied in pairwise comparison or compared to peripheral nerve blocks, the question which adjuvant or combination of adjuvants is the most effective in prolonging the duration of different types of local infiltration analgesia (LIA) has not been answered conclusively. OBJECTIVE: The objective of this network meta-analysis was to determine the analgesic effectiveness and safety of adjuvants in local infiltration analgesia. DESIGN: Systematic review of randomized controlled trials with network meta-analyses. DATA SOURCES: A comprehensive literature search in Embase, CENTRAL, MEDLINE and Web of Science was performed up to March 2023. RESULTS: The best interventions to prolong the duration of analgesia were dexamethasone (Ratio of Means (ROM) 3.33) followed by the combinations of clonidine + morphine (ROM 3.35) and morphine + magnesium sulfate (ROM 2.92), fentanyl (ROM 2.27), ketorolac (ROM 2.26), buprenorphine (ROM 2.04), morphine (ROM 1.93), magnesium sulfate (ROM 1.91), clonidine (ROM 1.89), dexmedetomidine (ROM 1.74) and tramadol (ROM 1.58). Serious adverse events were not reported with either investigated adjuvant. CONCLUSION: There is moderate evidence that dexamethasone is the most effective adjuvant to prolong the duration of analgesia in LIA. The evidence for the alpha-2 agonists dexmedetomidine and clonidine is also moderate, but their effectivity to prolong analgesia stays behind dexamethasone. Clonidine and dexmedetomidine had a small detectable effect on pain scores, yet below clinical relevance, but the largest effect on MEQ consumption. The effects of different opioids were homogenous for all endpoints. The prespecified subgroup analysis of LIA of the knee did not show significantly different results than the pooled analysis. STUDY REGISTRATION: PROSPERO 2020 CRD42020176154 (28.04.2020).