Efficacy and safety of dexmedetomidine as an adjuvant to local wound infiltration anaesthesia: A meta-analysis with trial sequential analysis of 23 randomised controlled trials.

To further identify the real efficacy and safety of dexmedetomidine as an adjuvant to local wound infiltration anaesthesia, we conducted this meta-analysis. The systematic search strategy was performed using PubMed, Embase, Cochrane Library, and Chinese databases. As a result, a total of 23 RCTs (1445 patients) were included. Patients receiving dexmedetomidine combined with local anaesthetics had a lower rescue analgesia rate [risk ratio (RR): 0.48; 95% confidence interval (CI): 0.36-0.65] and lower rescue analgesic consumption [weighted mean difference (WMD): -10.80 mg; 95%CI: -13.28 to -8.31 mg] than patients receiving local anaesthetics alone. The dexmedetomidine-related adverse reactions included bradycardia (RR: 1.33; 95%CI: 0.32-5.56) and hypotension (RR: 3.00; 95%CI: 0.49-18.42). In addition, the time to first analgesic request (WMD: 296.16 minutes; 95%CI: 165.69 minutes ~ 426.63 minutes), incidence of postoperative nausea and vomiting (PONV) and pain scores at 4 hours postoperatively were also significantly lower in patients receiving dexmedetomidine combined with local anaesthetics. This meta-analysis demonstrated that the use of dexmedetomidine as an adjuvant to wound infiltration is effective for reducing the rescue analgesia rate, rescue analgesic consumption and PONV. In addition, limited evidence shows that dexmedetomidine can prolong postoperative analgesia for approximately 5 hours. Further investigations on dexmedetomidine-related adverse reactions and the dose-response effect of dexmedetomidine in wound infiltration are warranted.

INTRODUCTION

Postoperative pain and opioid‐related adverse drug events are still among the principal factors affecting the rapid recovery and discharge of patients undergoing surgery. Wound pain at rest and on movement is one of the main sources of postoperative pain. In addition, skin traction stimulation, which can be caused by respiratory movement and the daily activities of patients after surgery, further aggravates the severity of wound pain, resulting in restlessness and insomnia and even inducing serious symptoms such as wound tear and infection. The technique of wound infiltration analgesia has been shown to play an active role in relieving postoperative pain and reducing opioid consumption.

Wound infiltration analgesia includes either local wound infiltration (LWI) or continuous wound infiltration (CWI) via a catheter. CWI has been shown to be effective but has also been found to be associated with increased difficulty in postoperative care, catheter detachment, and fluid leakage. , While LWI with a single local anaesthetic can be used to overcome these complications, the analgesic time is unsatisfactory. , By increasing the duration of action, dexmedetomidine (DEX), an α2‐agonist, may help avoiding the need for catheters insertions.

In a previous meta‐analysis conducted by our research team, the analgesic effect of DEX was not fully evaluated because of the small sample size and single analysis methods. Although this meta‐analysis favoured DEX, the type of surgery examined was limited to abdominal surgery. In addition, DEX‐related adverse reactions such as bradycardia and hypotension were not evaluated, and no trial sequential analysis (TSA) was conducted. These important topics have not been fully elucidated, and thus, it is important to further investigate the efficacy and safety of DEX in wound infiltration. Therefore, we conducted this meta‐analysis to evaluate the analgesic effect of DEX as an adjuvant to local anaesthetics vs local anaesthetics alone in wound infiltration. Furthermore, we conducted a comprehensive investigation of the occurrence of adverse reactions with the aim of gaining greater insights into the safety of DEX.

METHODS

Search strategy

Based on the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta‐Analyses) guidelines and the recommendations from the Cochrane Collaboration, a systematic search was performed using PubMed, Embase, the Cochrane Library, and Chinese databases [Chinese National Knowledge Infrastructure (CNKI) and Wan‐Fang database]. In addition, Google Scholar was used to retrieve grey literature. This meta‐analysis was registered in the PROSPERO database: CRD42020175117. The full search strategy is provided in the Appendix ( ).

The search included studies published prior to May 2020. A manual search was also performed to select articles and published reviews. Because this study is a meta‐analysis, there was no need for ethical approval and informed consent.

Study selection

Studies were included if they met the following criteria: (1) the study was a randomised controlled trial (RCT); (2) the study compared patients who received DEX as an adjuvant to local anaesthetics with patients who received local anaesthetics alone for local wound infiltration anaesthesia; (3) the study included a DEX group and placebo (PLA) group, at least; and (4) the full text of the study was available. There were no language restrictions. Studies were excluded if (1) they were abstracts, conference articles, and protocols, (2) they did not have complete data, or (3) DEX was given intravenously in the study.

Data retrieval

The extracted information included the name of the main author, the year of publication, the type of surgery, the sample size, the doses administered to the DEX group and the PLA group, and outcomes.

The following indexes were defined as primary outcomes: (1) the rescue analgesia rate within 24 hours after surgery, (2) the total rescue analgesic consumption in the 24‐hour postoperative period, and (3) the incidence of DEX‐related adverse reactions at 24 postoperative hours, that is, bradycardia and hypotension.

The secondary outcomes of this article include (1) the visual analogue score (VAS, ranging from 0 to 10; 0 corresponding to no pain and 10 representing the worst imaginable pain) at 1, 2, 4, 6, 8, 12, 24 and 48 hours postoperatively in the resting state, (2) the time of first rescue analgesia within 24 hours after surgery, and (3) the rescue analgesia of different frequencies. Other adverse events at 24 postoperative hours include postoperative nausea (PON), postoperative vomiting (POV), PONV, respiratory depression, shivering, dizziness, wound infection, sedation, and urinary retention.

Data reported in graphical form were derived by GetData Graph Digitizer Software (GetData Pty Ltd., Kogarah, Australia). The original data, which were represented by the median and interquartile range, were converted to the mean and standard deviation (SD) using the methods described by Wan et al. Using a published equivalence formula, cumulative opioid consumption with opioid drugs other than morphine was converted to morphine‐equivalent doses, where 10 mg intravenous (i.v.) morphine = 0.01 mg i.v. sufentanil = 0.1 mg i.v. fentanyl = 100 mg i.v. tramadol = 2 mg i.v. butorphanol = 50 mg i.v. diclofenac = 100 mg i.v. pethidine. Finally, the time of first rescue analgesia and the total morphine consumption are continuous outcomes that are measured in units of minutes and milligrams, respectively.

Qualitative assessment

The methodological quality of the included RCTs was reviewed by two reviewers (YFR and MLW) independently. The Cochrane Collaboration's risk of bias assessment tool was used. They evaluated the quality of each article using seven domains. If there were some disagreements, they discussed the disagreements to reach consensus, or the issue was decided by two other reviewers (WS and HL). Finally, low bias, high bias, and unclear judgements were obtained.

Statistical analysis

Measures of treatment effects

Review Manager 5.3 was used for statistical analysis. The total rescue analgesic consumption and the time of the first rescue analgesia were expressed by the weight mean difference (WMD) and its 95% confidence interval (CI). Dichotomous outcomes were expressed by the risk ratio (RR) and its 95% CI. The continuity correction was applied for zero‐event studies. A P value <.05 was considered statistically significant. VAS scores at different times after surgery are reported with 99% CIs (α corrected = 0.01) because a Bonferroni correction was applied.

Heterogeneity, sensitivity and subgroup analyses

The I 2 statistics were used to assess the heterogeneity of the studies. If the I 2 < 50%, heterogeneity was considered not significant, and the fixed‐effects model was applied; otherwise, we assumed that there was significant heterogeneity and used the random‐effects model to calculate effect size. If an I 2 > 50% was observed, sensitivity analysis and subgroup analysis were performed to explore the sources of heterogeneity. Sensitivity analysis was conducted by excluding studies in which the quality was rated as “high risk”. The following subgroup analyses were performed if more than five trials were included for the outcome: the time of incision infiltration (before skin incision vs before skin closure), the type of local anaesthetic (ropivacaine vs bupivacaine), the DEX dose (≤1.0 μg/kg vs >1.0 μg/kg) and the anaesthesia mode (general anaesthesia vs regional anaesthesia). A two‐sided P value <.05 was considered statistically significant.

Assessment of publication biases

The funnel plot was used to assess the possibility of publication bias in the primary outcomes, including more than 10 trials. We estimated funnel plot asymmetry using Begg and Egger tests, and a one‐sided P < .05 was considered to indicate significant publication bias. If a P value was less than .05, the trim‐and‐fill computation would be used to evaluate the effect of publication bias on the interpretation of the results. Stata 15.0 (StataCorp, College Station, TX) was used for assessment of publication biases.

Trial sequential analysis

The repeated updating of a meta‐analysis inevitably involves the repeated calculation of accumulated data, which results in the risk of random errors and false positives, especially in small sample sizes. Trial sequential analyses (TSA) can estimate and correct the potential random errors and estimate the robustness and reliability of the accumulated combined data in a meta‐analysis. Furthermore, TSA software can calculate the required information size (RIS). The RIS refers to the minimum sample size needed to achieve the maximum reliability on the basis of fully estimating the type I and type II errors. Therefore, a TSA was conducted to analyse the main outcomes by TSA software version 0.9 Beta (Copenhagen Trial Unit).

For dichotomous outcomes, a constant continuity correction was performed for zero‐event trials. We calculated the RIS based on the low risk of bias studies. D2 was described as a heterogeneity correction. The risk for a type I error was 5%, and the risk for a type II error was 20% (80% power). (1) For the rescue analgesia rate, the relative risk reduction (RRR) = 44.18%, the incidence in the DEX group = 40.07%, and the incidence in the PLA group = 71.79%; (2) for the incidence of bradycardia, RRR = −18.56%, the incidence in the DEX group = 1.15%, and the incidence in the PLA group = 0.97%; (3) for the incidence of hypotension, RRR = −105.41%, the incidence in the DEX group = 0.76%, and the incidence in the PLA group = 0.37%.

For continuous outcomes, we set the effect measure as “WMD” and the model as “Random Effects (DL)” in TSA software. The risk for a type I error was 5%, and the risk for a type II error was 20% (80% power). We calculated the RIS based on the low risk of bias studies. WMD = −9.65 mg with SD = 6.92 mg.

In the graph drawn by TSA software, when the Z‐curve crossed the conventional boundary and the TSA boundary value or directly crossed the RIS, we think that the current meta‐analysis conclusion is stable and reliable enough, and further research would not reverse this conclusion , ; when the Z‐curve crossed the invalid line and entered the invalid area, we think that there was no significant difference between the DEX group and PLA group; if the Z‐curve did not meet the requirements of the above two lines, it indicates that further clinical studies are needed to determine the effectiveness of the DEX group.

Summary of findings

GRADE (Grades of Recommendation, Assessment, Development, and Evaluation) Profiler 3.6 software was also used to evaluate the evidence quality of primary outcomes in our study, which was classified as high, moderate, low, or very low. Judgements included risk of bias, inconsistency, indirectness, imprecision, and other considerations.

RESULTS

Characteristics of the included studies

The search identified 415 studies, of which 368 were eliminated from further review because they were animal studies, non‐related studies, non‐original articles, or duplicates. After reviewing the full texts of the articles, 24 trials were excluded. Finally, 23 RCTs were considered to be suitable for this meta‐analysis, , , , , , , , , , , , , , , , , , , , , , , encompassing a total of 1445 adult patients. The search process is shown in Figure 1.

FIGURE 1

Study flow diagram for inclusion. RCTs, randomised clinical trials

Of the 23 studies, patients underwent surgery under spinal anaesthesia in 2 studies, , and other studies used general anaesthesia. , , , , , , , , , , , , , , , , , , , , Eight studies , , , , , , , involved wound infiltration before skin incision, and 15 studies , , , , , , , , , , , , , , concerned wound infiltration before skin closure. The types of local anaesthetics include ropivacaine, , , , , , , , , , , , , bupivacaine , , , , , , , , and lidocaine. The concentrations of ropivacaine were 0.2%, , , , 0.3%, , , 0.375%, 0.5% , , and 0.75% , ; the concentrations of bupivacaine were 0.25% , , , , , , , and 0.5% ; and the concentration of lidocaine was 2.0%. The doses of DEX were 0.5 μg/kg, , 1.0 μg/kg, , , , , , , , , , , , , 1.5 μg/kg, 2.0 μg/kg, , , , 5.0 μg/kg , and 50 μg. In one study, adrenaline (1: 200 000) was given with lidocaine. Different non‐opioid analgesics (tramadol, ketorolac, paracetamol, and diclofenac) were used for rescue analgesia in eight studies, , , , , , , , and 15 trials , , , , , , , , , , , , , , reported that patients received only opioids for rescue analgesia. The detailed characteristics of all the included studies are shown in Table 1.

TABLE 1

Study characteristics

Studies (year)	Surgery	Groups (n): Treatment (total volume)	Time of WI	Analgesic	Outcomes
Abdelnaim et al 16 (2018)	Hernia repair	DEX (15): 0.5% bupivacaine+1 μg/kg DEX+ NS (20 mL)	Before skin incision	Ketorolac	Rescue analgesia rate VAS scores Bradycardia, hypotension, PON, POV, PONV, respiratory depression
		PLA (15): 0.5% bupivacaine+ NS (20 mL)
Ahmed et al 17 (2020)	Lower segment caesarean section	DEX (30): 0.25% bupivacaine+1 μg/kg DEX+ NS (25 mL)	Before skin closure	Morphine	Rescue analgesia rate Rescue analgesic consumption Bradycardia, hypotension, PONV, dizzy
		PLA (30): 0.25% bupivacaine+ NS (25 mL)
Bhardwaj et al 18 (2017)	Lower segment caesarean section	DEX (30): 0.75% ropivacaine 3 mg/kg + 1.5 μg/kg DEX+ NS (40 mL)	Before skin closure	Tramadol	Rescue analgesia rate Rescue analgesic consumption Time to first request of analgesia VAS scores Bradycardia, hypotension, PONV, respiratory depression, wound infection, sedation
		PLA (30): 0.75% ropivacaine 3 mg/kg + NS (40 mL)
Bommalingappa et al 19 (2016)	Lumbar spine surgery	DEX (25): 0.25% bupivacaine+50 μg DEX + NS (15 mL)	Before skin closure	Acetaminophen	Rescue analgesia rate Time to first request of analgesia VAS scores Bradycardia, PON, POV, PONV, respiratory depression, shivering, dizzy
		PLA (25): 0.25% bupivacaine+ NS (15 mL)
Deshwal et al 20 (2018)	Lumbar discectomy	DEX (30): 0.2% ropivacaine+1 μg/kg DEX+ NS (30 mL)	Before skin closure	Fentanyl	Rescue analgesia rate Rescue analgesic consumption VAS scores Bradycardia, hypotension, PON, POV, PONV, respiratory depression, wound infection, sedation
		PLA (30): 0.2% ropivacaine+ NS (30 mL)
Jyothi et al 21 2020	Abdominal Surgeries	DEX (30): 0.25% bupivacaine+2 μg/kg DEX + NS (30 mL)	Before skin closure	Tramadol	Rescue analgesia rate Rescue analgesic consumption Time to first request of analgesia Bradycardia, hypotension, PON, respiratory depression
		PLA (30): 0.25% bupivacaine+ NS (30 mL)
Kang et al 22 (2012)	Inguinal herniorrhaphy	DEX (26): 0.2% ropivacaine+1 μg/kg DEX + NS (10 mL)	Before skin incision	Fentanyl	Rescue analgesic consumption VAS scores PON, POV, PONV, dizzy, sedation, urinary retention
		PLA (26): 0.2% ropivacaine+ NS (10 mL)
Kim et al 23 (2014)	Hemorrhoidectomy	DEX (19): 0.2% ropivacaine+5 μg/kg DEX + NS (20 mL)	Before skin incision	Fentanyl	Rescue analgesic consumption VAS scores PONV, urinary retention
		PLA (21): 0.2% ropivacaine+ NS (20 mL)
Li et al 24 (2019)	Lumbar Fusion Surgery	DEX (29): 0.5% ropivacaine+1 μg/kg DEX + NS (20 mL)	Before skin incision	Morphine	Rescue analgesia rate Rescue analgesic consumption Time to first request of analgesia VAS scores Bradycardia, hypotension, PONV, dizzy, wound infection
		PLA (28): 0.5% ropivacaine+ NS (20 mL)
Li et al 25 (2018)	Breast cancer	DEX (40): 0.375% ropivacaine+1.0 μg/kg DEX + NS (20 mL)	Before skin closure	Sufentanil	Rescue analgesia rate VAS scores Bradycardia, hypotension, PONV, respiratory depression, dizzy, wound infection, sedation, urinary retention
		PLA (40): 0.375% ropivacaine+ NS (20 mL)
Luan et al 26 (2017)	Open gastrectomy	DEX (23): 0.3% ropivacaine+1.0 μg/kg DEX + NS (22 mL)	Before skin closure	Sufentanil	Rescue analgesic consumption VAS scores PON, POV, PONV
		PLA (23): 0.3% ropivacaine+ NS (22 mL)
Mandal et al 27 (2016)	Reconstructive maxillofacial surgery	DEX (38): 2% lignocaine+1 μg/kg DEX+ NS (15 mL)	Before skin incision	Sufentanil	Rescue analgesic consumption Time to first request of analgesia Bradycardia, hypotension, PON, POV, PONV, dizzy, sedation, urinary retention
		PLA (38): 2% lignocaine+ NS (15 mL)
Mitra et al 28 (2017)	Lumbar discectomy	DEX (15): 0.5% ropivacaine+0.5 μg/kg DEX+ NS (22 mL)	Before skin closure	Diclofenac	Rescue analgesic consumption Time to first request of analgesia VAS scores Bradycardia, hypotension, PON, POV, PONV, respiratory depression
		PLA (15): 0.5% ropivacaine+ NS (22 mL)
Mohamed et al 29 (2018)	Abdominal hysterectomy	DEX (30): 0.25% bupivacaine+2 μg/kg DEX+ NS (40 mL)	Before skin closure	Morphine	Rescue analgesia rate Rescue analgesic consumption Time to first request of analgesia VAS scores Bradycardia, hypotension, PON, POV, PONV, respiratory depression, sedation
		PLA (30): 0.25% bupivacaine+ NS (40 mL)
Ranjita et al 30 (2016)	Total laparoscopic hysterectomy	DEX (40): 0.2% ropivacaine+0.5 μg/kg DEX+ NS (40 mL)	Before skin closure	Diclofenac	Rescue analgesia rate Rescue analgesic consumption Time to first request of analgesia VAS scores PON, POV, PONV
		PLA (40): 0.2% ropivacaine+ NS (40 mL)
Selvaraj et al 31 (2019)	Laparoscopic cholecystectomy	DEX (58): 0.25% bupivacaine+2 μg/kg DEX+ NS (24 mL)	Before skin incision	Ketorolac	Rescue analgesia rate VAS scores PONV
		PLA (58): 0.25% bupivacaine+ NS (24 mL)
Singh et al 32 (2017)	Abdominal hysterectomy	DEX (28): 0.25% bupivacaine+1.0 μg/kg DEX+ NS (30 mL)	Before skin closure	Morphine	Rescue analgesia rate Rescue analgesic consumption VAS scores
		PLA (30): 0.25% bupivacaine+ NS (30 mL)
Tan et al 33 (2018)	Laparoscopic cholecystectomy	DEX (20): 0.3% ropivacaine+1.0 μg/kg DEX+ NS (24 mL)	Before skin closure	Butorphanol	Rescue analgesic consumption Time to first request of analgesia VAS scores PONV
		PLA (20): 0.3% ropivacaine+ NS (24 mL)
Ülgey et al 34 (2015)	Total abdominal hysterectomy	DEX (25): 0.25% bupivacaine+2.0 μg/kg DEX+ NS (40 mL)	Before skin incision	Pethidine	Rescue analgesia rate Rescue analgesic consumption VAS scores Bradycardia, hypotension, PON, POV, PONV, respiratory depression, wound infection
		PLA (25): 0.25% bupivacaine+ NS (40 mL)
Vallapu et al 35 (2018)	Postcraniotomy	DEX (50): 0.25% bupivacaine+1 μg/kg DEX+ NS (20 mL)	Before skin closure	Acetaminophen	Rescue analgesia rate Rescue analgesic consumption Time to first request of analgesia VAS scores
		PLA (50): 0.25% bupivacaine+ NS (20 mL)
Wu et al 36 (2019)	Breast cancer	DEX (55): 0.3% ropivacaine+5.0 μg/kg DEX+ NS (250 mL)	Before skin closure	Pethidine	Rescue analgesia rate VAS scores PONV, shivering, sedation
		PLA (55): 0.3% ropivacaine+ NS (250 mL)
Xia et al 37 (2017)	Retroperitoneal laparoscopic	DEX (30): 0.75% ropivacaine+1.0 μg/kg DEX+ NS (11 mL)	Before skin closure	Dezocine	Rescue analgesia rate VAS scores PONV, shivering
		PLA (30): 0.75% ropivacaine+ NS (11 mL)
Yu et al 38 (2016)	Laparoscopic cholecystectomy	DEX (35): 0.5% ropivacaine+1.0 μg/kg DEX+ NS (30 mL)	Before skin incision	Pethidine	Rescue analgesic consumption VAS scores
		PLA (35): 0.5% ropivacaine+ NS (30 mL)

Abbreviations: DEX, dexmedetomidine; PLA, placebo; NS, normal saline; VAS, visual analogue scores; PON, postoperative nausea; POV, postoperative vomiting; PONV, Postoperative nausea and vomiting.

Study quality and risk of bias

The risk‐of‐bias assessment for all included studies was performed by two independent reviewers (YFR and WML). All included studies provided clear inclusion and exclusion criteria. An adequate randomization method was used in all articles. Thirteen RCTs explicitly specified the method of allocation concealment (via opaque‐sealed envelopes). , , , , , , , , , , , , Nine studies , , , , , , , , and 1 study, respectively, were assessed as having an unclear bias or high bias because of the absence of explicit or no mention of allocation concealment methods. Sixteen studies , , , , , , , , , , , , , , , had a low risk of bias as a result of the blinding of participants and personnel; however, 3 trials , , were rated as being at a high risk of detection bias because there was no indication of how participants or personnel were blinded. Five trials , , , , were rated as an unclear risk because of incomplete outcome data. Most of the studies (13 out of 23) , , , , , , , , , , , , were assessed as having an unclear risk of other bias because of the lack of sufficient methodological reports. Overall, seven studies , , , , , , had a low risk of bias, 13 studies , , , , , , , , , , , , had an unclear risk of bias, and 3 studies , , had a high risk of bias. The quality assessment for each study and the results of the included RCTs are shown in Figure 2.

FIGURE 2

Methodological quality and bias risk. Green circle = low bias risk, yellow circle = unclear bias risk, red circle = high bias risk

Primary outcomes

Total rescue analgesia rate within 24 hours after surgery

The total rescue analgesia rate was assessed by 16 studies. , , , , , , , , , , , , , , , Patients in the DEX group required less rescue analgesia than patients receiving local anaesthetics alone (RR: 0.48; 95% CI: 0.36‐0.65; P < .00001; I 2 = 91%) (see Figure 3A).

FIGURE 3

Total rescue analgesia rate within 24 hours after surgery. (A) Forest plot. (B) Trial sequential analyses (TSA). RIS, required information size; DEX, dexmedetomidine; PLA, placebo. Red line: cumulative Z‐curve; blue line: conventional boundary for benefit; green vertical line: required information size of a meta‐analysis

Sensitivity analysis did not show any changes in heterogeneity (Table S1A). The subgroup analysis showed that compared with the control group, the DEX group had a significantly reduced the rate of total rescue analgesia regardless of the type of local anaesthetic, the DEX dose, the type of anaesthesia, and the type of incision infiltration. It should be noted that wound infiltration performed before skin closure led to a significant reduction in the total rescue analgesia rate (RR: 0.49; 95% CI: 0.35‐0.69; P < .0001; I 2 = 90%); however, no significant difference was observed when wound infiltration was performed before skin incision (RR: 0.43; 95% CI: 0.13‐1.44; P = .17; I 2 = 90%) (Table B).

The TSA results showed that the cumulative Z‐curve crossed both the traditional boundary and the TSA boundary. Therefore, the accumulated sample information of the current studies reached the expected value, indicating that the rescue analgesia rate of the DEX group was significantly lower than that of the PLA group (see Figure 3B).

Egger's test showed that there was asymmetry in the funnel plot (P = .000). However, the adjusted effect estimate obtained via trim and fill analysis (with no study added) indicated that the data were unchanged (see Figure ). This finding suggests that publication bias does not significantly affect the stability of the pooled results.

We graded the quality of the evidence for the “total rescue analgesia rate” as “moderate” (downgraded because of publication bias).

Total rescue analgesic consumption within 24 hours after surgery

Twenty studies , , , , , , , , , , , , , , , , , , , investigated postoperative analgesic requirements within 24 hours after surgery, 2 trials , reported insufficient graphical information to allow for extraction, and 3 studies , , were not included in the meta‐analysis because their results were not reported. Thus, of the 20 studies, 15 , , , , , , , , , , , , , , had complete data to allow statistical analysis. Compared with local anaesthetics alone, the addition of DEX significantly reduced the consumption of rescue analgesic (morphine equivalent, mg) by 10.80 mg (95% CI: −13.28 to −8.31 mg; P < .00001; I 2 = 98%) (see Figure 4A).

FIGURE 4

Postoperative rescue analgesic consumption within 24 hours (mg, intravenous morphine equivalents). A, Forest plot. B, Trial sequential analyses (TSA). RIS, required information size; DEX, dexmedetomidine; PLA, placebo. Red line: cumulative Z‐curve; blue line: conventional boundary for benefit; green vertical line: required information size of a meta‐analysis

In addition, sensitivity analysis and subgroup analysis were performed because the heterogeneity was above 50%. The effects were accentuated when comparing before skin incision vs before skin closure, ropivacaine vs bupivacaine, and ≤1.0 μg/kg vs >1.0 μg/kg. However, the results were similar when comparing general anaesthesia (WMD: −10.84 mg; 95% CI: −13.52 to −8.17 mg; P < .00001; I 2 = 98%) vs regional anaesthesia (WMD: −10.83 mg; 95% CI: −13.05 to −8.61 mg; P < .00001; I 2 = 0%) (Tables A, B).

A TSA for postoperative equivalent consumption of morphine showed an RIS of 279 participants, and the cumulative Z‐curve also crossed both the traditional boundary and the TSA boundary, demonstrating that firm evidence was established with respect to the sample size (see Figure 4B).

A funnel plot constructed using Egger's test showed the presence of publication bias (P = .009). However, the adjusted effect estimate obtained via trim and fill analysis suggested that no trimming was performed, and the data were unchanged (see Figure ). So, it suggests no concern that the presence of publication bias has resulted in exaggerated summary effects.

We graded the quality of the evidence for the “analgesic requirement” as “moderate” (also downgraded because of publication bias).

Incidence of bradycardia and hypotension

The most common adverse events following DEX administration, namely, bradycardia and hypotension, were reported by 11 (623 patients) , , , , , , , , , , and 10 (547 patients) , , , , , , , , , of the included trials, respectively. Only one study reported that seven patients experienced bradycardia after surgery (4 in DEX group and 3 in PLA group) and there was no statistically significant difference between the groups (P = .69) (see Figure 5A). The results showed that the risk of hypotension was three‐fold after receiving DEX (RR, 3.00; 95% CI: 0.49‐18.42; I 2 = 0%), but there was also no statistically significant difference (P = .24) (see Figure 5A).

FIGURE 5

Forest plot for the outcome “incidence of DEX related adverse reactions”. A, Bradycardia. B, Hypotension. DEX, dexmedetomidine; PLA, placebo

Because heterogeneity was less than 50%, sensitivity and subgroup analyses were not needed.

The results of the TSA for bradycardia and hypotension showed that the current evidence was insufficient with respect to sample size (see Figure ).

We graded the quality of the evidence for 'bradycardia' and 'hypotension' as “low” (downgraded because of inconsistency and imprecision).

Secondary outcomes

Time of first rescue analgesia

Eleven studies , , , , , , , , , , reported the time of first rescue analgesia, and 2 , of these 11 trials were not included in the meta‐analysis because the only data reported were the means. Compared with receiving local anaesthetics alone, the addition of DEX significantly prolonged the time to first analgesic request by an average of 296.16 minutes (95% CI: 165.69‐426.63 minutes; P < .00001; I 2 = 100%) (see Figure 6A).

FIGURE 6

A, Forest plot for the outcome “time of first rescue analgesia within 24 hours after surgery”. B, Forest plot for the outcome “rescue analgesia rate of different frequency”. DEX, dexmedetomidine; PLA, placebo

As a result of the high statistical heterogeneity (I 2 = 100%), the sensitivity analysis and subgroup analyses were also used to analyse the sources of heterogeneity. The effect estimates remained robust in a sensitivity analysis excluding high‐risk trials (WMD: 268.26 minutes; 95% CI: 135.89‐400.63 minutes; P < .0001; I 2 = 100%) (Table A). Upon stratification of the data based on the type of local anaesthetic, compared with bupivacaine (WMD: 167.77 minutes; 95% CI: 110.22‐225.33 minutes; P < .00001; I 2 = 69%), it seems that ropivacaine is more effective in prolonging the time to first analgesic request (WMD: 392.37 minutes; 95% CI: 191.53‐593.20 minutes; P = .0001; I 2 = 100%) (Table B).

Rescue analgesia rate of different frequencies measurements within 24 hours after surgery

Considering that in some of the studies, the difference in the total rescue analgesia rate between the DEX group and the control group was not obvious, we tried to confirm the reliability of the postoperative analgesic consumption result through rescue analgesia of different frequencies measurement. Three studies , , evaluated the rescue analgesia rate of different frequency (once/twice/>twice). The results showed that the number of patients in the DEX group was higher than that in the control group in aspect of rescue analgesia of once (RR: 3.68; 95% CI: 1.80‐7.51; P = .0003; I 2 = 0%), but the number of patients in the DEX group was much lower than that in the control group when rescue analgesia was more than twice (RR: 0.18; 95% CI: 0.06‐0.55; P = .003; I 2 = 63%). No significant difference was observed when rescue analgesia was administered twice (RR: 1.26; 95% CI: 0.59‐2.71; P = .55; I 2 = 48%) (see Figure 6B). As a result of the limited number of included trials, sensitivity analyses, and funnel plot analyses were not performed.

The pain scores at different times postoperatively

Twenty trials , , , , , , , , , , , , , , , , , , , investigated the outcome “the pain scores at different times postoperatively”. Four , , , of these 20 trials were not included in the meta‐analysis because the only data reported were the means or because the data could not be extracted. VAS scores were used as a pain scoring tool in all 16 RCTs. The data can be combined and analysed only when the number of studies is more than two for a given outcome. VAS scores at 1, 2, 4, 6, 8, 12, 24, and 48 hours after surgery were analysed to assess pooled effects in this meta‐analysis.

The random‐effects meta‐analysis demonstrated that participants receiving DEX as an adjuvant to local anaesthetics had lower pain scores than those treated only with local anaesthetics at 1 hour (WMD: −0.78 cm; 95% CI: −1.11 to −0.45; P < .00001; I 2 = 86%), 2 hours (WMD: −0.64 cm; 95% CI: −0.85 to −0.43; P < .00001; I 2 = 71%), 4 hours (WMD: −1.00 cm; 95% CI: −1.26 to −0.73; P < .00001; I 2 = 95%), 6 hours (WMD: –0.59; 95% CI: −0.88 to −0.30; P < .0001; I 2 = 86%), 8 hours (WMD: −0.83 cm; 95% CI: −1.05 to −0.61; P < .00001; I 2 = 94%), 12 hours (WMD: −0.81 cm; 95% CI: −1.02 to −0.59; P < .00001; I 2 = 96%), 24 hours (WMD: −0.50 cm; 95% CI: −0.62 to −0.38; P < .00001; I 2 = 86%) and 48 hours (WMD: −0.31 cm; 95% CI: −0.48 to −0.14; P = .0004; I 2 = 95%) postoperatively (see Figure 7).

FIGURE 7

The forest plots of VAS pain score at 1, 2, 4, 6, 8, 12, 24, and 48 hours postoperatively on resting state. VAS, visual analogue scale. DEX, dexmedetomidine; PLA, placebo

We conducted a sensitivity analysis by excluding high‐risk bias trials, and the data remained robust (Table A). Next, we performed subgroup analyses with the remaining prespecified subgroups, but heterogeneity was not reduced below an I 2 of 50% in any of the subgroups with more than two trials (Table B).

Safety analysis

Adverse events

All included studies reported various side effects, three , , of which were excluded because of a lack of specific data. Thus, of the 23 studies, 20 , , , , , , , , , , , , , , , , , , , had complete data to allow for statistical analysis.

The most commonly reported adverse events were postoperative nausea (PON), postoperative vomiting (POV), PONV, and respiratory depression. Compared with the control group, patients receiving DEX had a reduced incidence of PON (RR: 0.61; 95% CI: 0.43‐0.86; P = .004; I 2 = 0%), POV (RR: 0.51; 95% CI: 0.28‐0.92; P = .03; I 2 = 0%), and PONV (RR: 0.50; 95% CI: 0.37‐0.69; P < .0001; I 2 = 0%). None of the studies reported the outcome of respiratory depression in patients (Figure 8).

FIGURE 8

The forest plots of the other adverse events. PON, postoperative nausea; POV, postoperative vomiting; PONV, postoperative nausea and vomiting. DEX, dexmedetomidine; PLA, placebo

On the other hand, our meta‐analysis focusing on shivering, dizziness, sedation, and urinary retention showed no significant differences between the DEX combined with local anaesthetics group and the local anaesthetics group. It is important to note that no patients with respiratory depression or wound infection were reported in any trial (Figure 8). Because of the low heterogeneity of all the results (I 2 < 50%) in this analysis and the limited number of studies included for some indicators, sensitivity, and subgroup analyses were not conducted.

DISCUSSION

The results of this meta‐analysis indicate that DEX as a local anaesthetic adjuvant used in wound infiltration could reduce the rescue analgesia rate (by more than twice) and reduce analgesic requirements within 24 hours after surgery with firm evidence according to the TSA. Furthermore, DEX significantly prolonged the analgesia time of wound infiltration by approximately 5 hours and decreased the VAS score at 4 hours postoperatively (the magnitude of the decrease was 1). Our study also shows that DEX does not significantly increase the incidence of transient or reversible side effects but significantly reduces the incidence of PON, POV, and PONV. However, it is equally important to note that there is not enough evidence to confirm that DEX has nothing to do with the occurrence of postoperative bradycardia and hypotension according to the TSA results.

Efficacy of local DEX in wound infiltration analgesia

In this meta‐analysis, because VAS is greatly affected by subjective factors , and there are few studies that have examined the time to first rescue analgesia, the more objective indicators of rescue analgesia rate and analgesic consumption were selected as the primary outcomes.

This meta‐analysis identified 23 RCTs that compared DEX combined with anaesthetic and anaesthetic alone in wound infiltration. The results of the rescue analgesia rate and analgesic consumption were consistent, especially that the rescue analgesia rate of more than twice in DEX group was significantly lower than that in the anaesthetic alone group. Nonetheless, we urge caution in interpreting the rescue analgesia of different frequencies measurement data given that only three trials were included in this group. In addition, we demonstrated for the first time within the TSA that the evidence is powered sufficiently by a large number of RCTs so that studies do not need to investigate the effect of the rescue analgesia rate and analgesic consumption following DEX combined with local anaesthetics in the future.

In the subgroup analysis, we tried to explore the source of heterogeneity through the types of local anaesthetics, the doses of DEX and so on. Although the results are robust, we must admit that our exploration did not find substantial evidence of reduced heterogeneity. In these subgroup analyses, we focused on the dose of DEX. The meta‐analysis or RCTs examining the brachial plexus block , , showed that DEX had a dose‐dependent effect on prolonging the analgesia time and reducing the consumption of analgesics; that is, increasing the dose of DEX would prolong the analgesia time and reduce the consumption of analgesics. Curiously, low‐dose DEX (≤1.0 μg/kg) seems to be more effective than high‐dose DEX (>1.0 μg/kg) in our subgroup analysis, but this result is only inferential and needs to be carefully explained. This result is consistent with the TSA results, further emphasising the need to focus on the dose–response effect of DEX in future research.

In terms of the pain score, the VAS was used as the evaluation method in all included studies, which is very important for reducing clinical heterogeneity. We analysed the VAS at eight time points in the resting state within 48 hours after surgery. Compared with local anaesthesia alone, DEX modestly reduced the resting VAS pain scores and benefit up to 48 hours after surgery. However, the reduction of the combined effect was inferior, and the magnitude of decrease was more than 1 point only at 4 hours postoperatively (typically, this is considered clinically significant).

Safety of local DEX in wound infiltration analgesia

Because the local administration of DEX is an off‐label use, it is important to fully report possible adverse events before using DEX as a local anaesthetic adjuvant to wound infiltration. We concluded that there were no significant differences in the side effects related to DEX (bradycardia, hypotension), , respiratory inhibition, wound infection, and other adverse reactions between the DEX group and the placebo group. In contrast, the use of DEX reduced the incidence of PONV, an effect associated with reduced postoperative pain and opioid use. If we only analyse the research results, the local use of DEX seems to be relatively safe, and wound infiltration with DEX will not lead to wound infection. However, the TSA results showed that the total number of patients analysed is too low to clearly understand the evidence of side effects related to DEX; further research may overcome this limitation.

Therefore, after comprehensive consideration, the overall quality of evidence for DEX‐related side effects was rated as 'low' according to the GRADE approach. It is necessary to carry out large‐scale RCTs on these adverse events before DEX is formally used for wound infiltration in adult patients.

Strengths and limitations

Our research has several advantages and potential limitations. First, this research is based on a meta‐analysis conducted by our team that is in previous study, and our interpretation of the results is cautious; the GRADE rating of the evidence base is conservative. Second, in this meta‐analysis, we analysed the results by TSA, sensitivity analysis, subgroup analysis, publication bias (including trim‐and‐fill computation), and GRADE rating to further appraise the robustness of the results and provide ideas for future research directions. Last, compared with our previous meta‐analysis, we comprehensively evaluated the safety of DEX in this study, which is profoundly significant for clinical medication.

The most important limitation of the study is the high heterogeneity of the primary outcomes. First, both sensitivity analysis and subgroup analysis cannot continuously reduce heterogeneity, which may have a negative impact on the external validity of our results. This indicates that in addition to our predetermined subgroup analysis, other potential sources of heterogeneity (such as the type of surgery, the depth of wound infiltration, and the type of postoperative analgesics) may affect the consistency of studies. The above factors, together with other internal factors, might lead to a high degree of heterogeneity in all RCTs. Second, the trim‐and‐fill computation showed that the primary indicators are robust, and the TSA shows that the evidence of the main indicators is enough. However, there is a significant publication bias that cannot be ignored, which is one of the reasons why the two foremost pain indicators were rated as “moderate” by the GRADE approach. Finally, we were unable to explain why DEX's effect varies with local anaesthetics, and low‐dose DEX seems to be better for prolonging postoperative analgesia. Although this may be related to the quality of the methodology in the included trials, future research should focus on the evaluation of the dose response of DEX.

Conclusions

In conclusion, the meta‐analysis of 23 RCTs demonstrated that DEX combined with local anaesthetics significantly reduced the rescue analgesia rate and analgesic consumption compared with local anaesthetics alone (both moderate‐quality evidence). Other benefits of DEX included prolonged time to first rescue analgesia (approximately 5 hours), reduced early postoperative pain scores measured with the VAS (especially at 4 hours), and reduced PONV. As such, to optimise the analgesic effect of wound infiltration, DEX is a reasonable option as an adjuvant to local anaesthesia in clinical practice. However, as a result of the local injection of DEX currently being off‐label in wound infiltration and the low‐quality evidence of DEX‐related side effects (bradycardia and hypotension), we must emphasise the importance of conducting the necessary trials focusing on the adverse events and dose–response effects of local DEX.

CONFLICT OF INTEREST

All authors declare no conflict of interest.

Table S1A Sensitivity analyses for Total rescue analgesia rate

Table S1B: Subgroup analyses for Total rescue analgesia rate

Figure SP1: (A) Eggers's publication bias plot. (B) Funnel plot of the trim‐and‐fill computation for Total rescue analgesia rate.

Table S2A: Sensitivity analyses for Postoperative Analgesic Requirement within 24 h after surgery

Table S2B: Subgroup analyses for Postoperative Analgesic Requirement within 24 h after surgery

Figure SP2: (A) Eggers's publication bias plot. (B) Funnel plot of the trim‐and‐fill computation for postoperative analgesic requirement within 24 h after surgery

Figure SP3: Trial sequential analyses (TSA) for “incidence of DEX‐related adverse reactions”: (A) Bradycardia. (B) Hypotension. RIS, required information size. Blue line: cumulative Z‐curve; red line: conventional boundary for benefit.

Table S3A: Sensitivity analyses for Time of first rescue analgesia

Table S3B: Subgroup analyses for Time of first rescue analgesia

Table S4A: Sensitivity analyses for VAS scores

Table S4B: Subgroup analyses of VAS pain scores.

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