Efficacy and safety of electroacupuncture for postoperative bowel obstruction after abdominal surgery: A systematic review and meta-analysis

Abstract

BACKGROUND

Postoperative ileus (POI) and delayed bowel function recovery remain common challenges after abdominal surgery, even in the context of enhanced recovery after surgery protocols. Electroacupuncture has been increasingly investigated as a low-drug-burden adjunctive intervention for promoting gastrointestinal motility and modulating postoperative neuroimmune responses. However, existing clinical studies vary in patient populations, surgical types, intervention protocols, and outcome definitions, making the overall efficacy and safety of electroacupuncture uncertain.

AIM

To systematically evaluate the efficacy and safety of electroacupuncture as an adjunctive strategy for postoperative bowel function recovery after abdominal surgery, with particular attention to POI-related outcomes, clinical recovery indicators, adverse events, and the certainty of current evidence.

METHODS

PubMed, EMBASE, Web of Science, the Cochrane Library, CNKI, Wanfang Data, VIP, and SinoMed/CBM were searched electronically for clinical studies on electroacupuncture for POI or other closely related non-mechanical postoperative bowel motility recovery disorders after abdominal surgery from January 1, 2006 to March 1, 2026. Two reviewers independently performed literature screening, data extraction, and risk-of-bias assessment. Meta-analysis was conducted using RevMan 5.4. Continuous outcomes were expressed as mean difference (MD) with 95% confidence intervals (95%CIs), and dichotomous outcomes as odds ratio (OR) with 95%CIs.

RESULTS

A total of 9 studies were included. Meta-analysis showed that electroacupuncture significantly shortened time to first flatus (MD = -10.91 hours, 95%CI: -15.07 to -6.74, P < 0.00001) and time to first defecation (MD = -19.80 hours, 95%CI: -28.60 to -11.01, P < 0.0001) in patients after abdominal surgery, and also reduced postoperative length of stay (MD = -0.93 days, 95%CI: -1.67 to -0.18, P = 0.01). In addition, electroacupuncture reduced the risk of prolonged/persistent POI (OR = 0.45, 95%CI: 0.33-0.60, P < 0.00001) and appeared to facilitate earlier ambulation (MD = -9.37 hours, 95%CI: -18.34 to -0.40, P = 0.04). Some studies reported mild adverse events, and no definite serious adverse events were described; however, safety reporting remained generally insufficient.

CONCLUSION

The present empirical data suggest that electroacupuncture might facilitate the recovery of bowel function after abdominal operations, mainly by decreasing the time to the first flatus and the first bowel movement, reducing the occurrence of prolonged POI, and possibly shortening the hospital stay and allowing an earlier start of physical exercise. Considering the differences among the various studies regarding the type of operation, treatment methods and the evaluation of therapeutic effects, as well as the lack of information about the safety aspects, these findings should be interpreted with caution. Further research, including high-quality, multi-centre and uniform investigations, is necessary to confirm these results.

Key Words: Electroacupuncture; Postoperative ileus; Abdominal surgery; Bowel function recovery; Meta-analysis; Safety

Core Tip: This systematic review and meta-analysis suggest that electroacupuncture can significantly accelerate postoperative bowel recovery after abdominal surgery—shortening time to first flatus and defecation, reducing hospital stay, and lowering the risk of prolonged postoperative ileus—without serious adverse events reported. However, due to study heterogeneity and limited safety data, further high-quality research is warranted.

INTRODUCTION

Postoperative ileus (POI) still plays an important role in the recovery process after abdominal surgery and is related to some serious medical consequences. It mainly refers to the temporary inhibition of gastrointestinal movement without any mechanical reason[1]. The common symptoms include abdominal distension, nausea and vomiting, delayed gas or stool discharge, difficulty in taking in oral food and varying degrees of abdominal discomfort, which can seriously affect the early recovery after surgery[2]. In medical discussions and some research papers, the term “intestinal obstruction after surgery” is sometimes used when there is obvious disturbance in intestinal peristalsis, but in most cases, the underlying pathological abnormality continues to exist rather than being structural[3]. Based on the above explanation, the present review focuses on the investigation of POI and the related non-mechanical post-surgical intestinal motility abnormalities, while paying attention to the overall situation of post-surgical intestinal dysfunction in routine clinical treatment. Since the recovery of intestinal function is closely connected with the progress of nutrition, early walking, change of analgesic therapy and the possibility of hospital discharge, POI is usually one of the main factors slowing down the recovery rate after surgery[4]. Although there is no complete standardization in the diagnosis and endpoint definitions in this field, recent research has gradually clarified the differences between physiological post-surgical intestinal inhibition, extended POI and recurrent POI, thereby improving the understanding of the results of the studies[5].

The clinical importance of POI is not only reflected in the increase of patient discomfort, but also in its effect on the entire course of postoperative recovery[6]. For a considerable number of patients, intestinal dysfunction does not occur independently; instead, it is usually associated with delayed food intake, reduced physical activity, increased supportive care, and treatments such as gastrointestinal decompression, continuous intravenous fluid administration or close medical observation. If the recovery of bowel function is delayed, the resumption of oral nutrition support is often slowed down, early walking after operation may be hindered, the pain control methods may become more complex, and the length of hospital stay may be prolonged. From the perspective of perioperative care management, these consequences are significant because they delay the achievement of important recovery goals and reduce the overall effectiveness of enhanced recovery programs. In the field of current colorectal surgery, the incidence of POI is still relatively high and its economic impact should not be underestimated[7]. Large-scale database studies have shown that POI is closely related to higher consumption of health resources and increased inpatient costs, and recent meta-analyses have also confirmed the global economic burden of POI after abdominal operations. Therefore, POI is not a minor and temporary postoperative unpleasant feeling, but a crucial clinical event which affects both the quality of recovery and the efficiency of healthcare services.

The developmental process of POI is very complicated and cannot be explained by a single basic pathway. Previous studies indicate that there exists a multifaceted pathophysiological model which includes the inhibitory neural reflexes induced by surgical manipulation, the inflammatory reactions in the muscular layer of intestine, the increased postoperative sympathetic activity, the suppression of gastrointestinal movement by opioids, and the additional effects caused by excessive fluid administration, intestinal wall swelling and metabolic disorders. According to relevant evidence, the severity and the prolonged period of POI are jointly influenced by the extent of bowel manipulation during surgery, the degree of operative damage, the intensity of postoperative pain and individual differences in inflammatory response and autonomic function. Importantly, the initial neurogenic stage and the subsequent inflammatory stage do not occur independently but have mutual influences throughout the entire process, thus maintaining the inhibited gastrointestinal contractions and delayed functional recovery[8]. This complexity of the underlying mechanisms partly explains why the traditional single-target treatments often fail to produce consistent and uniform effects in different surgical patients, and it also suggests that therapeutic methods capable of targeting multiple biological pathways might have better prospects in this clinical situation.

The development of enhanced recovery after surgery (ERAS), particularly in colorectal surgery, has led to an improvement in the perioperative management protocols. By using minimal invasive surgical methods, multi-modal pain control methods, reducing the usage of opioid drugs, initiating oral intake early and implementing ambulation measures early, ERAS has changed the previous concepts of post-operative recovery and promoted a new approach to rehabilitation. However, although ERAS clinical procedures can reduce post-operative complications and shorten the hospital stay, the persistent problem of POI has not been completely eliminated. In the process of ERAS implementation, the prolonged existence of POI is still a common complication, and various influencing factors such as intravenous administration of opioid drugs have been found out by clinical researches. Furthermore, the fact that POI still occurs even after the improvement of clinical procedures suggests that the conventional supportive care might be insufficient for a large number of patients[9]. Some specific pharmaceuticals, like alvimopan, show good effects in certain clinical situations, but their application in actual clinical practice may be limited due to factors such as availability, economic burden, approved uses and differences in institutional clinical procedures. Therefore, the non-pharmacological adjunctive measures which are practical and safe deserve systematic investigation.

Among the additional clinical methods, the neuromodulatory interventions derived from acupuncture have received increasing attention in the last decade. From the perspective of gastrointestinal movement function, previous studies and clinical reviews show that acupuncture and electroacupuncture may affect gastrointestinal peristalsis, autonomic nervous system output and the formation of clinical symptoms, and have a regulatory effect on various motility disorders[10]. For the treatment of perioperative patients, the advantage of this kind of therapy lies in the possibility of adjusting the postoperative physiological state without adding a heavy pharmacological load to the patients. It is noteworthy that the acupoint sites such as Zusanli (ST36) and Neiguan (PC6) are frequently mentioned in both basic and clinical researches concerning the modulation of gastrointestinal functions, which has strengthened the theoretical basis of electroacupuncture as a therapeutic means for postoperative use. In other words, electroacupuncture is now considered not only as a supplementary approach based on experience and targeting symptoms, but also as a possibly biologically relevant modifier for the recovery of postoperative intestinal function.

The biological basis of electroacupuncture has become clearer in recent years. Experimental studies show that electroacupuncture given at ST36 can regulate gastrointestinal motility through vagovagal and sympathetic reflex pathways, thus providing a neurophysiological explanation for its prokinetic effects[4]. Further neuroanatomical research indicates that the autonomic modulation caused by electroacupuncture has certain regional specificity; for example, under certain conditions, stimulation of the hindlimb instead of the abdominal area can activate the vagal-adrenal anti-inflammatory pathway[11]. This is particularly relevant to POI, since postoperative bowel dysfunction is closely related to neuroimmune signaling and local inflammatory reactions in the intestinal wall. Therefore, the therapeutic value of electroacupuncture lies in its ability to affect both neural regulation and inflammatory responses in the pathogenesis of POI[12]. This dual modulation may help to explain why some clinical trials have found early improvements in flatulence, defecation, oral intake tolerance and mobility in patients undergoing electroacupuncture treatment. Although these physiological and clinical findings have not yet formed a complete mechanistic model, they provide a relatively consistent theoretical basis for future evidence integration.

Increasing research has shown that the present clinical evidence still indicates a great difference in the methodological designs[13]. Previous systematic reviews have suggested that acupuncture interventions might benefit the recovery after surgery; however, many evidence combining studies have classified manual acupuncture at acupoints, electroacupuncture and transcutaneous electrical acupoint stimulation into one group, although these treatment methods are not completely similar in their basic characteristics[14]. The research groups performing these syntheses have usually included various types of surgical patients in the broad concept of postoperative intestinal dysfunction. Moreover, the measurement criteria used in different studies vary greatly: Some focus on the time when flatus or defecation occurs for the first time, some emphasize the recovery of the ability to consume oral food, and others use the extended postoperative quality of intestinal function as the main endpoint of the study. Some review articles have also pointed out that the general quality of the existing evidence is relatively low to moderate, and larger scale clinical trials with more rigorous research designs are still required. Consequently, it is still unclear whether electroacupuncture, as a distinct kind of intervention, can provide measurable therapeutic effects and acceptable safety for postoperative intestinal function (POI) after abdominal operations.

In the present study, a comprehensive collection of evidence and statistical analysis were used to evaluate the therapeutic effect and safety of electroacupuncture for the postoperative bowel dysfunction after abdominal surgery, focusing on the recovery-related outcomes associated with postoperative nausea and vomiting (PONV) and the closely related non-mechanical bowel motility disorders. By setting up rigorous inclusion criteria to restrict the intervention method to electroacupuncture and combining the newly published clinical research data, the aim of this work is to provide a more precise assessment of several important recovery indicators, including the time to first flatus passage, the time to first bowel movement, the length of hospital stay after operation, the persistent PONV/persistent/prolonged POI (PPOI) and early postoperative ambulation. Considering that the available research includes both the perioperative measures aimed at restoring bowel function or preventing the development of PONV/PPOI and the therapeutic studies involving patients with confirmed PONV/PPOI, we interpret the combined analytical results from the overall perspective of postoperative bowel function recovery instead of limiting them to a particular treatment situation. Thus, through this analytical approach, we try to assess the possible additional benefit of electroacupuncture in the modern perioperative recovery procedures, while being consistent with the actual clinical practices.

MATERIALS AND METHODS

Literature search strategy

The literature retrieval has been carried out according to the standard procedure for systematic reviews and meta-analyses. The search period ranged from January 1, 2006 to March 1, 2026. The databases containing English language materials include PubMed, EMBASE, Web of Science and the Cochrane Library. While Chinese language information sources are CNKI, Wanfang Data, VIP and SinoMed/CBM. In order to minimize possible omissions, we have also examined the reference lists of the included studies and related overviews manually.

A set of standardized subject headings and free-text lexical items was applied for literature retrieval. The main English search terms comprise "electroacupuncture", "electro-acupuncture", "postoperative ileus", "prolonged postoperative ileus", "paralytic ileus", "abdominal surgery", "colorectal surgery", "gastrectomy", and "randomized controlled trial", with necessary modifications according to the features of each database. The primary Chinese search terms are "electroacupuncture", "postoperative ileus", "postoperative bowel obstruction", "paralytic ileus", "abdominal surgery", "gastrointestinal surgery", "colorectal cancer", "gastric cancer", and "randomized control". No limitations have been imposed on the nationalities or geographical regions.

Enrolment qualifications and elimination benchmarks

We have formulated the inclusion criteria using the Population, Intervention, Comparison, Outcomes, and Study design framework.

Inclusion criteria: (1) Participants: Patients who have received medical treatment and shown POI or persistent/PPOI after abdominal surgeries, or subjects undergoing abdominal surgery during the recovery period of intestinal functions who provide relevant data; (2) Intervention: Electroacupuncture; (3) Comparison: Simulated electroacupuncture, routine medical care, standard treatment, or no acupuncture intervention; (4) Outcomes: At least one of the following endpoints must be recorded: Time taken for the first flatus passage, time taken for the first bowel movement, time taken for the reappearance of intestinal peristalsis sounds, time taken for resumption of oral food intake, time taken for independent walking, hospital stay after operation, incidence of prolonged POI/PPOI, or adverse effects; and (5) Study design: Randomized controlled trials or clinical investigations with available information for meta-analysis.

Exclusion criteria: (1) Manuscripts or researches which contain duplicated published materials or reused experimental data; (2) Case reports, case series, narrative reviews, meeting records, in vivo animal experiments, pathway investigation studies or research proposals without a control group; (3) Research programs where the administered treatment is not solely electroacupuncture, such as electroacupuncture combined with herbal rectal perfusion, acupoint substance administration or abdominal massage, and the individual effect of electroacupuncture cannot be clearly distinguished; (4) Studies which do not involve patients suffering from postoperative primary ovarian insufficiency or non-mechanical intestinal peristalsis recovery disorders after abdominal surgery, or researches focusing on confirmed adhesions, inflammations or other mechanical intestinal obstructions which do not correspond to the main objective of the current systematic review; or (5) Lack of complete manuscript or absence of essential outcome data which cannot be converted into valid information.

Screening of eligible investigations and acquisition of research data

Two reviewers checked the relevant literature separately. They excluded the irrelevant papers by reading the titles and abstracts. Afterwards, the full texts were judged according to the specified inclusion and exclusion criteria. If there was any disagreement between the two reviewers, it was settled by a discussion, and in certain situations, the decision was finally confirmed by a third reviewer.

We have gathered the necessary information from the finished research papers: (1) Basic details: Such as the first author, the publishing year, the place where the study was carried out and the design of the experiment; (2) The clinical characteristics of the selected subjects: Including the number of samples, age range, sex distribution, type of surgical operation, previous medical history and so on; (3) Properties of the applied intervention: Such as the choice of acupoints, the frequency and intensity of stimulation, the length of each treatment session, the frequency of intervention delivery and the entire therapeutic period; (4) Characteristics of the comparison group: Sham electroacupuncture, routine clinical care or the contents of standard therapeutic programs; and (5) Outcome measurements: Time to the first flatus passage, time to the first bowel movement, time to the restoration of intestinal peristaltic sounds, time to the resumption of oral food intake, length of postoperative hospital stay, incidence of delayed POI /partial POI, unfavourable events and so forth. For studies using multi-arm designs, predetermined analysis methods were used to combine the intervention groups or control groups during the meta-analysis process in order to avoid counting the participants in the control groups twice.

Quality assessment

The methodological quality of the enrolled studies was independently assessed by two research reviewers. We have evaluated the randomized controlled trials using the Cochrane risk-of-bias tool, considering aspects such as random sequence generation, allocation concealment, blinding, completeness of outcome data, selective reporting and other possible sources of bias. Each aspect is classified as low risk, high risk or with some concerns. Disagreements were resolved by discussion among the reviewers.

To carefully evaluate the correctness of the research results, we have classified the reliability of the evidence by applying a pre-determined method. In the first step of this evaluation, the evidence is divided into four categories, from high reliability to insufficient evidence. Each study included in the summary is independently reviewed by two trained assessors and any differences of opinion are settled by referring to an experienced expert. For the assessment of the strength of evidence, we take into consideration several key aspects of the study design and execution such as the bias risk in each investigation, the similarity of effect sizes in different groups, the connection between the intervention and the outcome measures, and the accuracy of the reported effect estimates. Besides, we also take into account the unpublished data or grey literature which may affect the total certainty of the gathered evidence. The reliability of the evidence will decrease if any of the following situations occur: Major methodological mistakes leading to a high risk of systematic errors, significant inconsistency in the results among different studies without an explanation by subgroup analysis, indirect comparison rather than direct trial, or small sample sizes resulting in wide confidence intervals for the effect estimates. On the other hand, the reliability of the evidence can be improved when large effect sizes are consistently observed in high quality studies or a dose-response relationship is clearly demonstrated between the exposure and the outcome variables. It is important to mention that the ultimate judgment on the credibility of the evidence reflects the level of confidence in the estimated effect size approaching the true underlying effect. This evaluation system aids in applying the research findings to clinical practice and policies by offering clear reasons for the strength of the recommendations given to medical practitioners and policy makers. All the decisions about the reliability of the evidence are recorded in standard formats which can be supplied upon request from the corresponding author of the study.

Two reviewers independently evaluated the strength of the evidence for each important result using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) system. At first, randomized controlled trials were judged as having high evidence strength, and their strength was then revised according to 5 aspects: The possibility of systematic bias, inconsistency of results, lack of directness of the evidence, impreciseness of the effect estimates and the existence of publication bias. The evidence strength was divided into four categories: High, moderate, low and very low. The research group has finished constructing a summary of findings table for all main outcomes, including the time needed for the first flatus passage, the duration till the first defecation, the hospital stays after surgery, the occurrence of delayed/POI, the recovery related to walking after operation and all the safety-related endpoints.

Statistical analysis

Meta-analysis was conducted with the help of RevMan 5.4. The continuous results were shown as mean difference (MD) with 95% confidence intervals (95%CIs) and the binary results as odds ratio (OR) or risk ratio with 95%CI. The heterogeneity between different studies was evaluated by χ² test and I² index. If P ≥ 0.10 and I² ≤ 50%, the heterogeneity was considered minor and a fixed-effects model was employed. When P < 0.10 or I² > 50%, it was regarded as considerable heterogeneity and a random-effects model was used, in which the possible causes of heterogeneity were investigated.

For the continuous measurement data recorded in the primary research papers in the form of median (interquartile range) or median (quartiles/range), appropriate calculation methods have been used to convert these values into mean ± SD before including them in the quantitative synthesis. In order to evaluate the influence of the transformed data on the reliability of the pooled effect estimates, a sensitivity analysis has been carried out when it is considered necessary. The results showing significant clinical differences have not been synthesized compulsorily and have been described narratively together with the findings of the original studies.

RESULTS

Literature search results

An original corpus of 371 bibliographic entries was got from the first search. After deleting 237 duplicates by using EndNote X9, 134 valid entries remained for subsequent processing. By examining the titles and abstracts of the documents, we excluded 107 studies which were clearly inappropriate for inclusion. A full document review was conducted for 27 manuscripts, of which 18 were dismissed: 10 because the research subjects or intervention measures did not meet the inclusion criteria, 6 due to the inappropriate research design, and 2 because the endpoint data could not be obtained or the manuscript repeated the previous results. Finally, 9 investigations were included in the systematic review and meta-analysis. The flow chart of the study selection process is shown in Figure 1, and the basic characteristics of the included investigations are listed in Table 1. These investigations cover both perioperative treatments to promote intestinal function recovery or prevent postoperative intestinal pain (POI)/persistent postoperative intestinal pain (PPOI), and therapeutic studies on patients with definite POI; therefore, the combined analysis results mainly indicate the general effect of electroacupuncture on the recovery of postoperative intestinal peristalsis function. The Cochrane risk-of-bias assessment tool was applied to evaluate the overall quality of the included investigations, showing that their methodological standards were satisfactory. Most studies had a low risk in generating random sequences and completing the endpoint data sets, but there were some uncertainties or insufficient disclosure in the aspects of allocation concealment, blind procedures and endpoint parameters (Figure 2).

Figure 1  Flowchart of literature selection.

Figure 2 Risk of bias assessment of the included studies. A: Risk of bias in the included studies; B: Summary of risk of bias.

Table 1 Basic Characteristics of the included studies (n = 9).

Ref.	Country/region	Study population/surgical type	Study design	Group size	Age (year)	Sex	Main notes
Meng et al[16], 2010	China	Patients after intra-abdominal surgery for colon cancer	Randomized controlled trial	EA group 44; conventional control group 41	Overall mean age 537; EA group 54.3; control group 53.1	Overall: 47 males, 38 females	Aimed at prevention of PPOI
Ng et al[20], 2013	Hong Kong (China)	Patients undergoing laparoscopic resection for colon cancer and upper rectal cancer	Prospective randomized three-arm trial	EA 55; Sham 55; No acupuncture 55	67.4 ± 9.7; 67.4 ± 10.7; 68.5 ± 10.6	Male/female: 35/20; 33/22; 31/24	Single-center study registered at ClinicalTrials.gov
Zhang et al[17], 2014	China	Patients undergoing elective open resection for malignant colorectal tumors	Randomized sham-controlled trial	EA 19; Sham EA 20	63 ± 9 vs 60 ± 10	Male/female: 11/8 vs 11/9	Thirty-nine patients completed the study; ST36 EA
Chen et al[21], 2024	China	Patients with clearly diagnosed POI after colorectal cancer surgery	Two-group controlled study using random number table	Treatment group 30; control group 30	63.53 ± 14.39 vs 61.83 ± 11.90	Male/female: 17/13 vs 15/15	Therapeutic study of postoperative POI
Yang et al[22], 2022	China	Patients after elective laparoscopic colorectal resection	Single-center, three-arm, prospective randomized trial	ST25-EA 35; ST36-EA 35; standard care 35	61.8 ± 11.0; 60.7 ± 12.7; 60.7 ± 10.5	Male/female: 18/17; 25/10; 23/12	Time to first flatus and first defecation as co-primary outcomes
Qiu et al[23], 2021	China	Patients with ileus after open surgery for gastrointestinal malignancies	Randomized controlled trial	EA group 45; conventional treatment group 45	Both groups approximately 57 (57 ± 12 vs 57 ± 14)	Male/female: 26/19 vs 19/26	Post-open-surgery gastrointestinal malignancy population
Wang et al[24], 2023	China	Patients after laparoscopic colorectal cancer resection	Multicenter, randomized, sham-controlled clinical trial	EA 125; Sham EA 123	60.2 ± 11.0 vs 60.2 ± 11.8	Male/female: 70/55 vs 83/40	Multicenter study under ERAS background
Shao et al[25], 2021	China	Patients after laparoscopic colorectal cancer surgery	Three-arm block-randomized trial	Randomized: Tianshu group 15; Zusanli group 15; conventional group 14; final analysis 12/11/13	62.9 ± 7.6; 57.3 ± 12.3; 59.0 ± 8.1	Male/female: 10/5; 10/5; 12/2	Small-sample three-arm study
Pei et al[26], 2025	China	Patients after laparoscopic gastrectomy for gastric cancer	Seven-center, three-arm, randomized trial	Randomized: EA 195; Sham 190; Standard care 195; FAS: 194/189/195	59.87 ± 9.93; 59.69 ± 10.60; 60.39 ± 10.13	Male/female: 127/68; 128/66; 134/55	Multicenter postoperative gastric cancer study

EA: Electroacupuncture; PPOI: Persistent/prolonged postoperative ileus; POI: Postoperative ileus; ERAS: Enhanced recovery after surgery.

Meta-analysis

Time to first flatus: Nine trials were selected, including 596 subjects in the experimental group and 800 in the control group. The heterogeneity test indicated moderate to high heterogeneity among the studies (I² = 67%, P = 0.002), so a random-effects model was applied. The meta-analysis showed that electroacupuncture could reduce the time to the first flatus in patients after abdominal operation, with a statistically significant result (MD = -10.91 hours, 95%CI: -15.07 to -6.74, P < 0.00001; Figure 3A). This suggests that electroacupuncture might promote the early postoperative recovery of gastrointestinal motility compared with the control treatments.

Figure 3 Forest plots of electroacupuncture plus standard care vs standard care or sham electroacupuncture plus standard care on postoperative gastrointestinal recovery outcomes. A: Time to first flatus; B: Time to first defecation; C: Bowel sound recovery time; D: Time to tolerability of liquid, semiliquid, and solid food; E: Length of postoperative hospital stay. 95%CI: 95% confidence interval.

Time to first defecation: Nine trials were selected, containing 597 subjects in the experimental group and 800 in the control group. The heterogeneity test indicated a high degree of heterogeneity among these studies (I² = 79%, P < 0.0001), thus a random-effects model was applied. The result showed that the time to the first defecation was significantly shorter in the electroacupuncture group than in the control group (MD = -19.80 hours, 95%CI: -28.60 to -11.01, P < 0.0001; Figure 3B). This result implies that electroacupuncture may not only accelerate the expulsion of intestinal gas after operation but also promote the overall bowel evacuation function.

Postoperative length of stay: Six investigations are included in the present study, involving 242 subjects in the intervention group and 253 subjects in the control group. The heterogeneity test shows moderate inconsistency among the enrolled studies (I² = 63%, P = 0.02), so a random-effects model is used for further calculation. The results of the pooled analysis indicate that the hospital stay after surgery is significantly shorter in the electroacupuncture group than in the control group (MD = -0.93 days, 95%CI: -1.67 to -0.18, P = 0.01; Figure 3C). This result suggests that electroacupuncture not only accelerates the post-surgical recovery but also has a beneficial effect on reducing the hospitalization period.

Prolonged/persistent POI: Four experiments were selected, including 410 subjects in the treatment group and 657 in the control group. The heterogeneity test indicated a good agreement among the studies (I² = 8%, P = 0.35), so a fixed-effects model was applied. The combined results demonstrated that electroacupuncture could decrease the probability of prolonged POI/PPOI significantly, with a statistically important difference (OR = 0.45, 95%CI: 0.33-0.60, P < 0.00001; Figure 3D). This finding implies that electroacupuncture might not only promote faster bowel recovery but also reduce the incidence of persistent postoperative bowel dysfunction.

Time to ambulation/independent walking: Four studies were considered in the present analysis, including 342 subjects in the intervention group and 542 in the control group. Since the definitions of activity resumption varied among the included studies, mainly concerning the time to walk or the time to walk independently, this endpoint was combined as a postoperative movement recovery index. The heterogeneity test showed moderate differences between the studies (I² = 55%, P = 0.08), and therefore a random-effects model was used for further calculations. The results indicated that the time of movement recovery was significantly shorter in the electroacupuncture group than in the control group (MD = -9.37 hours, 95%CI: -18.34 to -0.40, P = 0.04; Figure 3E). These findings suggest that electroacupuncture might have some benefits in promoting early postoperative mobility and speeding up the overall recovery process, although the present results should be interpreted cautiously due to the variations in the measurement of the outcome indicators.

Summary

From the above results, it is clear that electroacupuncture has significant clinical benefits for the recovery of intestinal functions after abdominal operations, especially in reducing the time to the first flatus and the first bowel movement, and decreasing the chance of prolonged POI/poor postoperative intestinal function. Some promising trends have also been observed in regard to shortening the hospital stay after operation and speeding up the early recovery of mobility. In summary, electroacupuncture might promote the recovery of gastrointestinal functions after surgery; however, since the included studies differ in their research backgrounds, type of surgery, intervention methods and criteria for measuring the outcomes, the obtained conclusions should be considered cautiously.

Certainty of evidence

Pursuant to the GRADE system, the confidence level of the supportive evidence is judged as low for the period before the first flatus, the time between the first defecation and the end of hospital stay after surgery, and the duration of post-surgery intestinal obstruction; moderate for the prolonged/ongoing post-surgery intestinal obstruction; and very low for the recovery related to post-operative walking and the safety-related endpoints. The main reasons for the downgrading of the evidence include the doubt about the existence of bias in the enrolled studies, the large differences in the selected continuous measurement points, the different concepts of the outcomes in various researches, and the poor record of adverse events. Therefore, although the overall results indicate a beneficial effect of electroacupuncture, the obtained data should be interpreted with proper caution, especially for the endpoints with high variability or inconsistent reporting (Table 2).

Table 2 Summary of findings and certainty of evidence for main outcomes.

Outcome	Number (studies)	Effect estimate	Certainty	Reasons for downgrading
Time to first flatus	1396 (9)	MD = -10.91 hours (95%CI: -15.07 to -6.74)	Low	Risk of bias; inconsistency
Time to first defecation	1397 (9)	MD = -19.80 hours (95%CI: -28.60 to -11.01)	Low	Risk of bias; serious inconsistency
Length of stay	495 (6)	MD = -0.93 days (95%CI: -1.67 to -0.18)	Low	Inconsistency; indirectness
Prolonged/persistent postoperative ileus	1067 (4)	OR = 0.45 (95%CI: 0.33-0.60)	Moderate	Risk of bias
Time to ambulation/independent walking	884 (4)	MD = -9.37 hours (95%CI: -18.34 to -0.40)	Very low	Inconsistency; indirectness; imprecision
Safety/adverse events	Not pooled	Mild adverse events reported; no definite serious adverse events described	Very low	Risk of bias; indirectness; very serious imprecision due to incomplete safety reporting

MD: Mean difference; OR: Odds ratio; 95%CI: 95% confidence interval.

DISCUSSION

The present systematic review and meta-analysis have shown that electroacupuncture is related to the improvement of several main recovery indicators after abdominal surgery, mainly including shorter time to the first passage of flatus and the first bowel movement, a lower probability of POI prolongation, and favorable changes in the length of hospital stay and activity recovery period. In summary, the promoting effect of electroacupuncture on postoperative gastrointestinal functional recovery seems relatively consistent in the included studies, but its influence on the length of hospital stays and the whole recovery course appears to be slightly weaker. It should be noted that the enrolled research works were not carried out in exactly the same clinical conditions: Some focused on the perioperative enhancement of intestinal function recovery or prevention of prolonged POI/PPOI, while the others investigated the curative treatment for patients with clearly confirmed POI. This suggests that the current results may be better interpreted as reflecting the potential function of electroacupuncture during the overall process of postoperative intestinal function recovery in patients with clinically diagnosed postoperative bowel impairment, with POI/PPOI being the main analysis, rather than in a single restricted therapeutic situation.

In accordance with the present understanding of the pathogenesis of POI, the discovered results are biologically reasonable. POI is closely related to the suppression of nerve reflexes, the aggregation of inflammatory cells, the dysfunction of the autonomic nervous system and the inhibitory effects of the drugs used during the perioperative period, especially opioids, on the motor function of the gastrointestinal tract[15]. Electroacupuncture has received special attention in clinical research because its underlying functional mechanisms are not limited to one single factor in the whole regulatory process[16]. Previous experimental and mechanistic studies have shown that electroacupuncture might regulate the output of autonomic nervous signals, change the transduction of the vagal pathway and reduce the inflammatory responses associated with the inhibited gastrointestinal movements. Moreover, the stimulation site may also have a considerable influence; for example, acupoints such as ST36 have been repeatedly found to be involved in the regulation of gastrointestinal function. Therefore, the available research data support the idea that electroacupuncture may have clinically significant therapeutic effects through overlapping neuroregulatory and anti-inflammatory pathways.

The decrease in the risk of prolonged POI/PPOI is particularly significant. A delay of several hours in flatus evacuation or defecation is clinically important, but it is more crucial to reduce the probability of persistent bowel dysfunction, since prolonged POI is closely related to the prolongation of nutritional recovery, the increase of hospital stay and the rise of medical expenses. Even in the present ERAS pathways, persistent POI is still common and opioid exposure is considered a modifiable risk factor. The results of our study show that electroacupuncture can help in reducing prolonged POI/PPOI. If this finding is confirmed in further researches, it will support the practical role of electroacupuncture in the perioperative recovery procedures[9].

In comparison with the recovery of the bowel, the effect of electroacupuncture on the length of postoperative hospital stay is favorable but of moderate size, which is not unexpected. The length of hospitalization is a comprehensive recovery endpoint influenced by various factors. Besides the recovery of gastrointestinal function, it is affected by postoperative adverse events, removal of drains, pain control, mobility ability, nutritional status, discharge rules and the implementation of clinical care procedures. Especially in the ERAS context, the discharge time is usually standardized and the influence of a single intervention may therefore be reduced. Therefore, although a statistically significant difference has been found in the length of hospital stay, the clinical significance of this result should be interpreted with caution and it should not be considered as the sole standard for evaluating the effectiveness of the intervention.

Although all the enrolled studies investigated the disturbances of postoperative bowel function during the post-surgical period, most focused on POI/PPOI or other non-mechanical motility disorders of intestine, while a few had a wider concept regarding the recovery of bowel function or post-operative intestinal dysfunction[17]. At the same time, the definitions of the measurement endpoints also vary in the existing literature. These differences do not deny the overall beneficial trend of the summarized results, but they suggest that the combined effect sizes should be interpreted as supporting evidence for a general therapeutic tendency rather than as a precise and universally applicable estimate of effect in all post-surgical clinical situations.

The safety profile is an important factor in evaluating the clinical feasibility of electroacupuncture. In the present systematic review, no definite severe adverse events associated with electroacupuncture have been found, and the adverse reactions observed were mainly moderate and self-limiting, such as temporary local discomfort, slight ecchymosis or remaining needle sensation. However, the recording of adverse events varies in different studies and some researches focus more on the evaluation of its efficacy rather than standard safety monitoring. Therefore, at present, it is more appropriate to state that electroacupuncture appears to be generally acceptable for postoperative use, rather than confirming its definite safety[18,19].

The current study has some notable disadvantages. Firstly, most of the present data come from small-scale single-center studies, which might result in unstable estimates and center-specific effects. Secondly, it is difficult to apply blinding in acupuncture research, and the differences between sham-controlled and no-treatment-controlled study designs may affect the patients' expectations and the effectiveness of the treatment[3]. Thirdly, some of the continuous outcome measures had to be converted from medians and interquartile ranges to means and standard deviations although appropriate calculation methods were used, the approximation errors cannot be completely avoided. Furthermore, the acupoint prescriptions and the parameters for electrical stimulation were not uniformly standardized in all the included studies, which may contribute to the clinical heterogeneity among the data sets. Lastly, since the enrolled studies vary in the type of surgery, the post-operative recovery environment and the definitions of the outcome indicators, the general applicability of the combined analysis results to particular clinical situations should be considered with caution[1,3,8].

Although there are some limitations, the present study still has some important theoretical and practical significances. From the clinical point of view, electroacupuncture is more appropriate as an additional treatment in the present procedures for perioperative recovery instead of being used as a substitute method. This is of great significance for the clinical decisions of the front-line doctors. The main principles of ERAS, the analgesic methods aimed at reducing the use of opioids and the evidence-based supportive treatments are the basic elements of the after-operation care. However, since POI still occurs even after the implementation of the modern clinical procedures, the supplementary treatment measures are still practically valuable. In the clinical situations where the pharmacological options are not available, contraindicated or have high cost-effectiveness, electroacupuncture can provide a feasible supportive alternative for the eligible patient groups.

Future academic investigations should not be limited to the question of whether electroacupuncture has a therapeutic effect, but should also consider more clinically important issues such as which patient groups are most suitable, when the treatment is most appropriate, and which treatment regimen is the best. Researchers have found that there is a need for more high-quality, multi-center, sham-controlled clinical trials with detailed records of the acupoint prescriptions, the electrical stimulation parameters, the starting times of the intervention and other accompanying therapeutic methods. It is important to standardize the definitions of the outcome for persistent obstructive pulmonary insufficiency (POI) and prolonged POI to improve the comparability between different researches. Additionally, the new studies should pay more attention to both the physiological measurement results and the clinical endpoints from the patients' point of view, such as the possibility of being discharged from the hospital, the patient's feeling of comfort, the acceptability of oral food intake and the quality of the recovery after the procedure.

In the holistic synthesis of previous studies, it is indicated that electroacupuncture might assist in accelerating the recovery of intestinal function after abdominal surgery, especially in shortening the time of flatus and first bowel movement and reducing the risk of postoperative intestinal paralysis. The results concerning the hospital stay duration after surgery, the recovery of early walking ability and the overall safety profile should be considered cautiously due to the differences among the included studies and the lack of sufficient evidence. Although there are still variations in the research designs and limitations in the strength of supporting evidence, the obtained findings support the view that electroacupuncture could be a possible complementary method in the current perioperative rehabilitation treatment, and provide a basis for further well-designed and mechanism-oriented clinical investigations in the future.

CONCLUSION

The results of the present study show that electroacupuncture might help improve the recovery of gastrointestinal functions after surgery for abdominal diseases, especially by decreasing the time to the first flatus passage and the initial defecation, and reducing the chance of prolonged POI. Some advantages have also been found in the length of hospital stay after operation and early walking after surgery. However, according to the GRADE evaluation system, the strength of the supporting evidence ranges from moderate to very low for all the measured endpoints. Therefore, although electroacupuncture may be a potential useful complementary method for the postoperative dysfunction of intestine, the present findings should be considered cautiously, particularly for those endpoints with great differences among studies or lack of sufficient safety information. Further well-designed multicenter and standardized researches are necessary for confirmation.