Twelve trials provided opioid consumption data at 24 hours. Pooled data found a statistically significant lower opioid consumption (WMD, −13.71; 95% CI, −17.83 to −9.60; P<0.001) in patients treated with combination of DEX and local anesthetic compared with local anesthetic alone (Fig. 7). Meta-regression showed that surgery types (P<0.001) were associated with the significant heterogeneity, whereas postoperative PCA (P=0.27), LA types (P=0.51), DEX doses (P=0.60) and anesthesia (P=0.28) did not contribute to the heterogeneity. Sensitivity analysis was typically performed to check the robustness of these results, with pooled WMDs ranging from −10.73 (95% CI, −14.90 to −71.68) to −15.14 (95% CI, −19.62 to −10.67). Begg’s funnel plot (P=0.41) and Egger’s test (P=0.076) showed no evidence of publication bias.
The duration of the TAP block was provided in 8 of the 20 included trials. Pooled results showed that DEX prolonged the block duration (WMD, 3.33; 95% CI, 2.85 to 3.82; P<0.001) (Fig. 8). Meta-regression showed that anesthesia (P=0.013) was associated with the significant heterogeneity, while surgery types (P=0.68), postoperative PCA (P=0.34), LA types (P=0.25) and DEX doses (P=0.48) did not contribute to the heterogeneity. Sensitivity analysis was typically performed to check the robustness of these results, with pooled WMDs ranging from 3.13 (95% CI, 2.74 to 3.53) to 3.49 (95% CI, 3.01 to 3.96). Begg’s funnel plot (P=0.9) and Egger’s test (P=0.52) showed no evidence of publication bias.
For adverse events, pooled analysis showed no difference in the incidence of PONV, hypotension, bradycardia, somnolence, hypotension, and pruritus between DEX and the control group (Table 3).
Postoperative pain remains a challenge worldwide. Inadequate treatment of pain can lead to patient anxiety, stress, extended hospital stays and dissatisfaction.37–39 Much attention has been paid to management of acute postoperative pain in recent years. The TAP block is a regional anesthetic technique that provides postoperative analgesia for abdominal surgery.40 The pooled results from our meta-analysis showed that DEX treatment reduced VAS pain scores by 0.78 points 8 hours postoperatively at rest and 1.13 points 4 hours postoperatively on movement. The lower pain scores can allow earlier ambulation after surgery and promote the satisfaction of analgesia of the patient. Meanwhile, opioid consumption was 13.71 mg lower in the DEX treatment group. Moreover, perineural DEX extended the duration of the TAP block by 3.33 hours compared with the control group.
Several recent studies demonstrated that DEX as potential LA adjuvant facilitates better and longer analgesia.41–43 The spinal and peripheral analgesic mechanisms of DEX could be contributed to its highly selective affinity to alpha-2 adrenergic receptor (α2AR).44 Similar to clonidine, DEX has an effect on presynaptic neuronal receptors and reduces norepinephrine release at peripheral afferent nociceptors.45 Furthermore, some evidence indicated that DEX played an inhibitory role in delayed rectifier K+ current and Na+ current, which resulted in a reduction in neuronal activity.46 Another study showed that adding DEX to ropivacaine increased the duration of analgesia by blocking the hyperpolarization-activated cation current.4 Our results were consistent with some recent meta-analyses that DEX as an adjuvant could prolong the duration of brachial plexus block.3–5 Currently, the safety of the perineural administration of DEX has received increased attention. In our study, DEX did not increase the incidence of hypotension or bradycardia. The low incidence of adverse events may be due to small dose of DEX administered.
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