Efficacy and Safety of Transcutaneous Electrical Acupoint Stimulation (TEAS) for Postoperative Pain in Laparoscopy: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Objectives This meta-analysis aimed to assess the efficacy and safety of transcutaneous acupoint electrical stimulation (TEAS) for postoperative pain in laparoscopy. The review has been registered on the “INPLASY” website and the registration number is INPLASY202150101. Methods Relevant randomized controlled trials are selected from seven electronic databases (PubMed, the Cochrane Library, Embase, China National Knowledge Infrastructure, Chongqing VIP Information, WanFang Data, and Chinese Biomedical Database) from their inception up to November 30, 2020. Twenty-eight studies were included in this meta-analysis, and the statistical analyses and the exploration of heterogeneity sources were conducted by Stata 15.0 software. Besides, the bias assessment of the included studies was evaluated using the Cochrane risk of bias tool. Results In total, 28 RCTs covering 2787 participants were included. The meta-analysis suggested that TEAS can effectively relieve pain in the short term after laparoscopy, reduce the postoperative consumption of rescue analgesics, improve the quality of life of patients, and shorten the length of hospitalization. And no serious adverse events are related to TEAS. Therefore, TEAS is relatively safe and efficacy for clinical application. The most used acupoints were Hegu (LI14), Neiguan (PC6), and Zusanli (ST36). Conclusions TEAS can be recommended as a complementary and alternative therapy for the treatment of postoperative pain after laparoscopy. However, the included RCTs had some methodological limitations. Therefore, larger-size, more rigorous, and higher-quality RCTs are needed in the future to further explore the efficacy and safety of TEAS for postoperative pain after laparoscopy.


Introduction
With the promotion of the concept of minimally invasive surgery, the application of laparoscopy has gradually increased because of its advantages of small trauma to surrounding tissues, less intraoperative bleeding, rapid postoperative recovery, and a wide application range. However, various types of pain such as incision pain, visceral pain, and nonincision pain often occur after laparoscopy, among which shoulder and back pain, diaphragm pain, intercostal muscle pain, and other nonoperative incision pain are more common [1]. is is a serious complication after laparoscopy, which is called "postlaparoscopic pain syndrome" [2]. It may be related to the following factors: the inflammatory injury or traction of the phrenic nerve caused by the residual CO 2 in the abdomen after the surgery, the proliferation of peritoneal inflammation induced by the acid environment in the abdomen, the humidity and temperature of the pneumoperitoneum, and the position and types of the surgery [3][4][5][6][7].
To some extent, postoperative pain may produce a negative effect on patients' physical activity, recovery time, quality of life, medical expenses, etc. erefore, optimizing the management of postoperative acute pain is crucial for accelerating postoperative rehabilitation. ough a variety of analgesic methods, such as nonsteroidal anti-inflammatory drugs (NSAIDs) or COX-2 analgesic drugs, as well as epidural analgesia, patient-controlled intravenous analgesia (PCIA), and nerve block, have been widely used in the clinic, they can also produce more side effects. For example, opioids can lead to postoperative nausea and vomiting, skin pruritus, respiratory inhibition, and other adverse reactions [8].
erefore, to reduce the side effects, many researchers began to turn to complementary and alternative therapies. One study [9] found that acupuncture and related techniques can significantly reduce postoperative pain score and opioid consumption and can be used as an effective auxiliary means of postoperative pain management. One study [10] reported that TEAS can significantly relieve postoperative pain and reduce opioid consumption on the first postoperative day. Another study [11] limited the mode of acupuncture to the way needling with penetration of the skin and only investigated the efficacy of such way on postoperative pain after laparoscopy and did not analyze the noninvasive acupoint stimulation mode.
Transcutaneous acupoint electrical stimulation (TEAS) is a noninvasive treatment formed by the gradual improvement of traditional acupuncture and moxibustion. During the operation, the specific low-frequency pulse current is input into the human body through the electrodes placed on the acupoints' surface and stimulates the acupoint to achieve a certain therapeutic effect, which combines the advantages of acupoint therapy and transcutaneous electric nerve stimulation (TENS). It can reduce the incidence of infection and bleeding, can be controlled or reused by patients and be operated by the operator after simple training, and has good treatment compliance. Many clinical randomized controlled trials (RCTs) have reported transdermal electrical stimulation is widely used in surgeries and plays a positive role in the treatment of postoperative pain [12][13][14]. In addition, pharmacological studies have shown that some medicinal plants are safe natural analgesics and have potential therapeutic advantages. For example, Molineria capitulata and Spirulina platensis have anti-inflammatory, antioxidant, and analgesic effects [15,16]. Bromelain is a natural drug to alleviate the symptoms of arthritis (including joint pain and stiffness) [17]. It has an active therapeutic effect on immune system diseases. Flavonoids can play an auxiliary role in the treatment of pain in the digestive system and nervous system [18].
ese studies may bring new clinical ideas to the treatment of postoperative pain. However, this time we are only going to evaluate the efficacy and safety of TEAS in the treatment of postoperative pain after laparoscopy, so we conducted this systematic review and meta-analysis. To our knowledge, this is the first metaanalysis focusing on the outcomes of TEAS in the treatment of postoperative pain after laparoscopy.

Materials and Methods
is systematic review and meta-analysis was performed in line with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) schema and was registered at INPLASY under registration number INPLASY202150101, and the corresponding protocol has been published in Medicine [19].

Data Sources and Search Strategy.
A comprehensive search was carried out in PubMed, the Cochrane Library (CENTRAL), Embase, and four Chinese databases (China National Knowledge Infrastructure, Chongqing VIP Information, WanFang Data, and Chinese Biomedical Database) from their inception up to November 30, 2020. Because of the language restriction of our researchers, only studies published in English and Chinese were included. e search strategy consisted of Medical Subject Heading (Mesh) terms and free-text terms with logical operators. Asterisks are truncation symbols that can help us search for all designs with asterisks. We performed an initial search of PubMed as follows (Table 1): #1 "transcutaneous electrical acupoint stimulation" OR "transcutaneous acupoint electrical stimulation" OR "electr * stimulat * " OR "electr * acustimul * " OR "electroacupuncture * " OR "electro-acupuncture" OR "TEAS"; #2 "Laparoscopy[Mesh]" OR "laparoscop * " OR "coelioscop * " OR "celioscop * " OR "peritoneoscop * "; #3 "Pain, Postoperative[Mesh]" OR "postoperative pain" OR "postoperative analgesi * " OR "pain management" OR "ache * " OR "suffering * " OR "discomfort." We also further searched the grey literature and the retrieved references to avoid omission. For the literature to be difficult to obtain the full text, we checked and identified the ongoing or unpublished studies through the World Health Organization International Clinical Trials Registry Platform (WHO ICTRP), Clinical Trials.gov, Chinese Clinical Trial Registry (Chi CTR), and the reference list of eligible RCTs. Two reviewers (Meng and Mao) independently screened the titles and abstracts for eligibility and examined the full text of the articles. Any discrepancies were resolved by consensus or after consulting a third party (Song).

Inclusion Criteria of Studies
(1) Participants: they were adults over 18 years old and underwent any kind of laparoscopy under general anesthesia. ere are no restrictions on gender, race, occupation, location, malignancy of the disease, and many other aspects. When these patients underwent surgery other than laparoscopy, we only analyzed the pain indicators related to laparoscopy.  [20] was used to assess the methodological qualities of the included trials by the two reviewers (Meng and Mao). e contents included random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, selective reporting, incomplete outcome data, and other risks of bias. e risk of bias was classified as "low-risk," "high-risk," or "unclear-risk." Disagreements in this interpretation were resolved via consensus or after discussion with a third party (Song).

Data Analysis.
Statistical analysis was performed with the Stata 15.0 software. P < 0.05 was considered statistically significant. For continuous variables, so the mean difference (MD) or standard mean difference (SWD) with 95% confidence interval (CI) was used for analysis. For dichotomous data, such as the rates of responders and adverse events, the relative risk (RR) with 95% confidence intervals (CIs) was utilized for analysis. In the multiarm RCTs, we only extracted the data related to our study. For studies that satisfied the predefined inclusion criteria with multiple intervention groups, which used different intervention duration or different acupoints, meta-analysis will be conducted carefully when merged the data into a unified intervention group data. e magnitude of heterogeneity was measured using heterogeneity index I 2 statistic: when I 2 < 50%, a fixedeffects model will be used for pooled data; when I 2 ≥ 50%, a random-effects model was used. For each merged analysis, a heterogeneity test was performed using the chi-squared statistic. If I 2 ≥ 50%, the synthesized studies were considered an indicator of a substantial level of heterogeneity. Subgroup or sensitivity analysis was performed to identify the cause. Subgroup analyses identified the possible factors that contributed to the heterogeneity, such as different intervention duration, interventions, types of surgery, and waveform. Funnel plots were introduced to detect the existence of potential publication bias within RCTs (n ≥ 10). If metaanalysis is not feasible, narrative descriptions are provided. If heterogeneity of significance found in the included studies cannot be explained by subgroup analysis, we will not conduct a meta-analysis.

Search Results.
A total of 238 articles were identified during the initial study selection, 82 duplicates were removed, and 121 articles were excluded after reviewing

#1
"transcutaneous electrical acupoint stimulation" OR "transcutaneous acupoint electrical stimulation" OR "electr * stimulat * " OR "electr * acustimul * " OR "electroacupuncture * " OR "electro-acupuncture" OR "TEAS" #2 "Laparoscopy[Mesh]" OR "laparoscop * " OR "coelioscop * " OR "celioscop * " OR "peritoneoscop * " #3 "Pain, Postoperative[Mesh]" OR "postoperative pain" OR "postoperative analgesi * " OR "pain management" OR "ache * " OR "suffering * " OR "discomfort" #4 #1 AND #2 AND #3 Evidence-Based Complementary and Alternative Medicine 3 abstracts and titles. Seven articles were excluded after reading the full text. For articles in which the data were repeatedly published, we choose the one with the higher quality and more related outcomes. Finally, 28 RCTs  met the eligibility criteria and were included in the systematic review. Standard general anesthesia was used in all trials. e PRISMA flow chart showed the study selection process in Figure 1.  [45][46][47][48] adopted the same measures as intervention groups besides TEAS. ere is a total of 14 acupoints, in which the most common acupoints are Zusanli (ST36), Nieguan (PC6), and Hegu (LI14). e intervention time was different and the duration from the time before anesthesia induction to the end of the operation was most commonly used. As we can see, the dilatational waveform and continuous waveform are commonly used. For stimulation frequency, 2/100 Hz and 2/10 Hz were popular among the trials. e main characteristics and the specific interventions of each identified study are presented in Table 2. Figure 2 summarizes the risk of bias in the 28 eligible RCTs, and the grade of the risk was recorded as "high-risk," "low-risk," and "unclear-risk." In terms of random sequence generation, 23 studies [21-35, 39, 41-44, 46-48] were considered as "low-risk" for they reported explicit random sequence methods, such as random number table method or computer-generated random number while others [36-38, 40, 45] were considered as "unclear-risk" for they only mentioned "random" or "randomization" and did not report the specific random sequence method. In terms of the methods of allocation concealment, 7 studies [22,24,28,32,43,47,48] were considered as "low-risk" for they reported the method of assigning concealment, while others did not report it. 10 studies [22-24, 27-29, 32, 34, 43, 47] were considered as "low-risk" which performed a blinding method on subjects and operators. 7 studies [22,24,28,32,40,43,47] were considered as "low-risk" which performed a blinding method on results evaluators. 27 eligible RCTs reported the planned outcomes, so they were associated with a "low risk" of bias for blinding of selective reporting while one study [47] was considered as "unclear risk" for it did not report the predesigned outcomes in the research protocol. One study [47] did not report missing data and was considered as "unclear risk," while other studies were considered as "low risk" for they reported the number and reasons of dropout members or no dropout members were in their studies. Additionally, the included 28 eligible RCTs did not report any details about potential sources of bias; therefore, they were considered as "unclear risk" in other biases.

Visual Analogue Scale (VAS).
Among the included studies, 8 studies were reported only in the form of graphs, without mean and standard deviation. However, our contact with the author is often unsuccessful. erefore, the data are often unavailable and can only be excluded. One study [43] recorded the mean VAS score and the most painful VAS score within 24 h after surgery. One study [26] recorded the incidence of shoulder pain 48 h after surgery. A study [23] recorded the postoperative Verbal Rating Scale (VRS) at different times. One study [36] reported 2 cases of VAS ≥ 4 in postoperative adverse reactions. Due to the insufficient number of studies reporting these data, no meta-analysis could be completed. Seventeen studies [25, 27, 29-31, 34, 35, 37-42, 44-46, 48] recorded VAS scores at different times after the surgery. erefore, to improve the validity of evidence, only studies (n ≥ 5 RCTs) reported VAS scores were analyzed to explore the analgesic effect of TEAS after laparoscopy.
Five studies reported a postoperative VAS score at 4 h ( Figure 3). e fixed-effects model was used with good homogeneity (P � 0.248, I 2 � 26.1%).
e combined data showed that the TEAS group was effective in reducing pain at this time compared with the control group [WMD � − 0.54, 95% CI (− 0.66, − 0.43),P < 0.001]. Six studies reported postoperative VAS scores at 6 h ( Figure 4). Due to obvious heterogeneity (P < 0.001, I 2 � 94.0%), a randomeffects model was used and showed no statistical difference between the two groups. e combined data extracted from 9 studies related to postoperative VAS score 12 h showed obvious heterogeneity (P < 0.001, I 2 � 73.8%), and a random-

e Postoperative Consumption of Analgesics.
In our study, the consumption of postoperative analgesics after laparoscopy was used as another important indicator to evaluate the analgesic effect of TEAS. Six studies [21,29,30,38,41,42] reported it. After our analysis, the postoperative consumption of analgesics 12 h was suitable for meta-analysis. ree studies [29,30,41] reported this outcome.
e fixed-effects model (Figure 7) was used according to no significant homogeneity (P � 0.943, I 2 � 0%). e combined data indicated that the postoperative consumption of analgesics was significantly lower in the TEAS group than that in the control group [SMD � − 0.87, 95% CI (− 1.12, − 0.63), P < 0.001].  Score. Five studies [21,22,34,43] reported the quality of recovery after surgery, in which four studies used the QoR-40 scoring scale, and one study [28] used the QoR-15 scoring scale. Four studies [21,22,34,43] reported postoperative QoR-40 scores at different times, in which one study [28] did not record in the form of mean ± standard deviation, so we excluded it. Based on the analysis of the data, the data of 24 h after surgery were considered suitable for meta-analysis.

Adverse Events.
Adverse events are the main evidence of safety evaluation. e adverse events in our study refer to a series of complications after the operation (e.g., nausea, vomiting, dizziness, pruritus, respiratory depression, etc.). In the 28 included studies, 6 [21,28,32,36,38,44] of which reported postoperative adverse events, while the remaining studies did not mention anything about safety evaluation. Mi et al. [21] recorded the incidence of nausea and vomiting in the treatment and control groups at different time points after surgery. And the comparison between groups at 4 h and 8 h after surgery showed statistical advantage (P < 0.05), but there was no significant difference at 24 h and 48 h after surgery. e results of Chen et al. [38] showed, that compared with the control group, there was no case of vomiting and shivering in the treatment group, and there were only two cases of nausea. e results of 4 studies [28,32,36,44] showed that no adverse events were observed throughout the procession of TEAS.

Sensitivity Analyses and Publication Bias.
To assess the stability of the study results, our study performed a sensitivity analysis on the meta-analysis one by one. It showed that the results of each meta-analysis were stable. A funnel plot was used to assess publication bias based on the VAS score at 24 hours after the surgery n ≥ 10 RCTs) ( Figure 10). It showed that most of the points were asymmetrically Evidence-Based Complementary and Alternative Medicine distributed around, indicating that there maybe have been some publication bias. Consistently, Egger's test ( Figure 11) suggested there is no publication bias in the RCTs (P � 0.261 > 0.05).

Discussion
Enhanced recovery after surgery (ERAS) advocates optimizing multiple approaches to perioperative pain management [49]. Postoperative analgesia is an important part of ERAS [50]. Nonincision pain is the most common complaint after laparoscopy, with an incidence of about 70%∼80% [51]. e continuous administration of analgesics will reduce the pharmacological effectiveness [52], and a series of side effects will be produced by opioids. erefore, there is an urgent need for optimized strategies to relieve postoperative pain after laparoscopy and improve the postoperative quality of life of patients.
To systematically assess the efficacy and safety of TEAS for postoperative pain after laparoscopy, our study conducted a systematic review and meta-analysis of 28 RCTs involving 2787 patients. Our meta-analysis suggests that TEAS can effectively relieve pain in the short term after laparoscopy, reduce the postoperative consumption of rescue analgesics, improve the quality of life of patients, and shorten the length of hospitalization. erefore, TEAS can be recommended as a complementary and alternative therapy for the treatment of postoperative pain after laparoscopy. Besides, no serious adverse events related to TEAS and the occurrence of treatment-related safety problems were reported in the included studies. erefore, we could think cautiously that TEAS is relatively safe and efficacy for clinical application.
A previous study suggested that epidural anesthesia can reduce postoperative pain scores in abdominal surgery [53], so it is often regarded as a confounding factor for electroacupuncture or electrical stimulation to exert postoperative analgesia [54]. erefore, our study only chose the operation of laparoscopy under general anesthesia, to avoid the interference of more potential factors. Pain intensity was selected as the outcome for it plays an important role in pain assessment and management [55]. VAS is commonly used in pain evaluation. Previous studies [56] have suggested that the subjectivity and multidimensionality of pain experience produce individual differences in pain assessment. Some studies showed that analgesic requirements are controlled by healthcare providers and are directly affected by the types of surgery and the economic status of patients. Analgesic consumption is not a particularly reliable indicator of the effectiveness of acupoint stimulation [57]. erefore, more objective indicators, such as the metabolism of pain substances in the blood, will be needed for postoperative pain assessment in the future.
Besides, we did not categorize different types of pain, which may affect the results. erefore, a more rigorous experimental design is needed to confirm the results of our study. We found that TEAS was effective in alleviating pain intensity at 4h, 12h, and 24h after laparoscopy, although this may depend on the type of surgery and waveform of the electrical stimulation device. TEAS can also effectively reduce the consumption of analgesics 12 h after surgery, but the sample size included in this study was small, and the pharmacological mechanism of different analgesics was not fully considered.
is indicates that TEAS can effectively relieve postoperative pain in the short term. However, in the process of future studies, more objective large-scale RCTs are still needed to provide more evidence support, and more attention should be paid to the standardized research program of TEAS and the follow-up of long-term efficacy.
At present, the analgesic mechanism of TEAS is not clear. Some studies [58][59][60] believe that the treatment process can cause the release of neurotransmitters in some regions of the spinal cord and brain, which increases the endogenous analgesic substances such as opioid peptides, strong kephalins, enkephalins, and acetylcholine, thus raising the pain threshold. It has been suggested that electrical stimulation can block pain signals by activating the descending inhibitory system in the brain stem [61]. It has been suggested that electrical stimulation activates different functional areas of the cerebral cortex, thereby reducing the body's sensitivity to painful stimuli by affecting the corresponding innervation of the skin [62].
For patients who have experienced laparoscopy, the body function is in a relatively weak state, resulting in patients with insufficient strength, blood stasis, and reduced meridians, resulting in postoperative pain symptoms. According to the traditional meridian theory of traditional Chinese medicine, the regulating effect of acupuncture and moxibustion is reflected not only in regulating the movement of Qi and blood, making the meridians and collaterals smooth, but also in regulating the ups and downs of Qi and blood, so that the organs and collaterals are supported by Qi and blood, and correcting the partial decline of the body. Acupoints are special parts of the viscera by draining Qi into the body surface. Electrical stimulation on the acupoints can play the role of regulating Qi and regulating blood, draining meridians, and dredging collaterals. Hegu (LI14), Neiguan (PC6), and Zusanli (ST36) are important acupoints for analgesia in meridian theory. Both ancient literature and modern studies show that Hegu (LI14) is good at relieving pain [63]. e experimental study [61] showed that the plasma concentration of 5-hydroxytryptamine (5-HT) decreased after electroacupuncture of Hegu (LI14) in rabbits, to achieve the purpose of analgesia. It can play an analgesic role in many ways, such as increasing the body pain threshold, alleviating microvascular spasms, and influencing the frontal cortex to participate in the discharge of the pain unit in the ventrolateral thalamic nucleus [64]. Besides, it has   Figure 11: Egger's test of publication bias.
Evidence-Based Complementary and Alternative Medicine 13 been reported to be effective in treating acute pain in various parts of the body [65]. Neiguan (PC6) has the effect of acute pain in various parts of the body [66]. Zusanli (ST36) has the functions of health care, immune regulation, strengthening and dispelling pathogenic factors, and regulating the spleen and stomach. Electroacupuncture stimulation of bilateral Zusanli (ST36) in rats can stimulate the parasympathetic nerve and cholinergic pathway, which can effectively promote the recovery of gastrointestinal function in rats [67,68]. ese acupoints are convenient and accurate, are easy to implement, and have good treatment compliance. e QoR-40 scale is designed to evaluate the quality of postoperative recovery. Its effectiveness has been verified clinically, and it is widely used to evaluate the quality of postoperative recovery [69]. e duration of hospitalization is also an important indicator of postoperative recovery. Our results are similar to those of the previous studies [54], which reported that TEA was effective in reducing the duration of hospitalization (MD � 1.30, 95% CI (− 2.10, − 0.51), I 2 � 32%, REM). Although this study has found that TEAS can improve postoperative quality of life and shorten the duration of hospitalization, more large RCTs with objective results are needed to confirm these findings.
For the aspects of the waveform and electrical stimulation frequency, the included studies mostly adopted dilatational waveform with 2/100 Hz. In terms of analgesia, a previous study [70] has suggested that the analgesic effect of alternating stimulation of density wave is better than that of simultaneous stimulation of different frequencies. TEAS used in 2/100 Hz induced the release of all opioid peptides and peptides with synergistic effects [71]. It can be seen that these research results are consistent with our data results. For the intervention time, most of the included studies were conducted from the time before anesthesia induction to after surgery. One study [72] has found that preoperative electroacupuncture therapy can relieve the tension and fear of patients and, to a certain extent, reduce the number of postoperative opioids for patients with mental stress. It has been shown that preoperative acupoint therapy interventions can reduce the need for opioids and opioid-related side effects after surgery [73,74]. However, one study [75] found that intraoperative treatment did not improve postoperative pain and did not reduce the amount of opioids needed. Besides, the brain will produce different responses with the different timing of acupuncture treatment, thus affecting the therapeutic effect [76]. erefore, it is suggested that the study on the timing of TEAS intervention should be strengthened and the treatment plan should be improved.

Limitations
It must be acknowledged that our meta-analysis has several limitations. (1) e intervention time, waveform, and frequency of electrical stimulation, acupoints, and other aspects of TEAS treatment are not uniform due to the different clinical experiences. At the same time, the treatment regimens in the control group were not uniform, which may affect the accuracy of the effectiveness assessment. (2) Our review may be affected by a high degree of heterogeneity, and it is difficult to find out the main reason that affects the efficacy of TEAS. (3) We did not distinguish between different types of pain and did not summarize the optimal TEAS treatment for postoperative laparoscopic pain. (4) Most RCTs were conducted in China, which may lead to publication bias and affect the validity and reliability of the system evaluation. (5) e methodological deficiencies and small sample size of the included trials may overestimate the efficacy to some extent. (6) No long-term follow-up information has been reported, so long-term efficacy remains to be confirmed.

Conclusions
In this systematic review and meta-analysis, TEAS can be cautiously considered as a treatment for postoperative pain after laparoscopy, which is effective in alleviating pain in the short term, reducing the use of remedial analgesics, and improving postoperative quality of life and length of hospital stay. TEAS is a noninvasive and easy-to-operate treatment, which can be operated after simple training, low application price, and good treatment compliance. It is worthy of clinical promotion and application. Although this study has limitations, it provides a direction and basis for future research. Due to the methodological deficiencies of the included RCTs, larger-size, more rigorous, and higher-quality RCTs are needed in the future to further explore the efficacy of TEAS in the treatment of postoperative pain after laparoscopy. erefore, it is necessary to further optimize the treatment plan in terms of intervention time, electrical stimulation frequency and waveform, and acupoint selection. e longterm therapeutic effect of TEAS needs further studies determined by the observation of prolonged follow-up time. Besides, more attention should be paid to the economic impact of TEAS in the health care system.

Data Availability
(1) is systematic review and meta-analysis was performed in line with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) schema and was registered at INPLASY under registration number INPLASY202150101; the hyperlink is https://inplasy.com/ inplasy-2021-5-0101/. (2) e corresponding protocol has been published in Medicine; the doi is 10.1097/ MD.0000000000026348.

Disclosure
Dan Meng and Yifei Mao are the co-first authors.

Conflicts of Interest
e authors declare that there are no conflicts of interest concerning this work. manuscript editing. D. Meng is responsible for the metaanalysis study selecting and manuscript writing. All authors read and approved the final manuscript. D. Meng and Y.F. Mao contributed equally to this work.

Supplementary Materials
In the supplementary files, there are seven sensitivity analyses, which are sensitivity analysis of VAS for postoperative 4 h, 6 h, 12 h, and 24 h, sensitivity analysis of QoR-40, sensitivity analysis of postoperative consumption of analgesics, and sensitivity analysis of duration of hospitalization. Sensitivity analysis can also be understood as robustness analysis, which is an important method mainly used to evaluate the robustness and reliability of the combined results of the meta-analysis. It is a common sensitivity analysis method to remove each included study one by one and then merge the effect quantity, changing the inclusion and exclusion criteria or removing a certain type of literature and then merging the effect quantity.
rough the sensitivity analysis of this study, we can confirm that all results are stable and reliable. (Supplementary Materials)