The Efficacy and Safety of Laparoscopy for Blunt Abdominal Trauma: A Systematic Review and Meta-Analysis

The efficacy and safety of laparoscopy for blunt trauma remain controversial. This systemic review and meta-analysis aimed to evaluate the usefulness of laparoscopy in blunt trauma. The PubMed, EMBASE, and Cochrane databases were searched up to 23 February 2021. Meta-analyses were performed using odds ratios (ORs), standardized mean differences (SMDs), and overall proportions. Overall, 19 studies with a total of 1520 patients were included. All patients were hemodynamically stable. In the laparoscopy group, meta-analysis showed lesser blood loss (SMD −0.28, 95% confidence interval (CI) −0.51 to −0.05, I2 = 62%) and shorter hospital stay (SMD −0.67, 95% CI −0.90 to −0.43, I2 = 47%) compared with the laparotomy group. Pooled prevalence of missed injury (0.003 (95% CI 0 to 0.023), I2 = 0%), nontherapeutic laparotomy (0.004 (95% CI 0.001 to 0.026), I2 = 0%), and mortality (0.021 (95% CI 0.010 to 0.043), I2 = 0%) were very low in blunt trauma. In subgroup analysis, recently published studies (2011–present) showed lesser conversion rate (0.115 (95% CI 0.067 to 0.190) vs. 0.391 (95% CI 0.247 to 0.556), test for subgroup difference: p < 0.01). This meta-analysis suggests that laparoscopy is a safe and feasible option in hemodynamic stable patients with blunt abdominal trauma.


Introduction
The use of laparoscopy on patients with trauma was first reported in the 1970s [1]. In the initial stage, the purpose of laparoscopy was only the diagnosis, and consequent open laparotomy was performed in cases that needed further procedures such as vessel ligation, bowel resection, or suture. The early reports of laparoscopy focused on only the diagnostic role. Several studies have reported that diagnostic laparoscopy in patients with trauma has a high diagnostic accuracy of nearly 100% [2]. Diagnostic laparoscopy is beneficial in avoiding unnecessary nontherapeutic laparotomy, which is usually accompanied by more complications than laparoscopy [3]. Moreover, with the development of the laparoscopic technique and equipment, therapeutic laparoscopy has been attempted on patients with trauma. There has recently been an increase in the number of reports on therapeutic laparoscopy in patients with trauma [4]. Recently, the laparoscopic procedure comprises both diagnostic and therapeutic purposes. As the therapeutic role of laparoscopy is increasing, the indication is widening, and unnecessary laparotomy is decreasing.
In terms of injury mechanism, compared to penetrating abdominal trauma (PAT), few studies have been conducted on laparoscopy in patients with blunt abdominal trauma (BAT). This may be because there are many ambiguous blunt regions, such as hematoma and bruised organs. In addition, laparoscopy for BAT and PAT is mostly performed in

Quality Assessment
The Newcastle-Ottawa quality assessment scale (NOS) was used to evaluate the risk of bias in the observational studies [25]. The NOS uses a star system with the following three domains: selection, comparability, and exposure/outcome. All studies were independently reviewed by two investigators. Any disagreement concerning study selection and data extraction was resolved through consensus.

Statistical Analysis
All statistical analyses were performed using the "meta" package of the R programming language, version 4.0.3 (R foundation, Vienna, Austria). The meta-analyses were performed using ORs for binary outcomes and standardized mean differences (SMDs) for continuous outcome measures and overall proportion for single proportional outcomes. Pooled analysis was performed using the inverse variance method with random effects weighing for meta-analysis of outcomes. Heterogeneity was assessed through visual inspection of the forest plots and estimated by using I 2 statistics and Cochran's Q (Chi-square test) (results with p-value < 0.10 were considered significant). I 2 statistics of >25%, >50%, and >75% were considered to represent low, moderate, and high heterogeneity, respectively [26].
Due to the few eligible studies (<20), we could not assess publication bias using statistical methods (e.g., funnel plots and Egger regression test) [27].
We performed subgroup analysis to assess the between-study heterogeneity. We divided the study groups by two moderators, such as the year of publication and type of injured organ. In terms of publication year, we defined two groups as follows: before 2010 vs. 2011 to present. The type of injured organ was categorized as follows: "general abdominal organ" referred to all general abdominal organs, including solid and hollow viscus organ. "Solid organ" referred to the liver or spleen. "Hollow viscus organ" referred to the upper or lower gastrointestinal tract. We did not conduct the subgroup analysis unless there was sufficient statistical power (small number of studies, k < 10).
We performed sensitivity analysis after excluding studies that comprised only the liver or spleen because they included substantially heterogenous indications. If the results did not change significantly after excluding those studies, then we considered that the results were robust. If the results changed significantly, we considered that the results were unstable.

Quality Assessment
All the included studies were observational studies. The quality assessment and risk of bias for each eligible study are summarized in Table 2. According to the NOS system, we found that all studies had an insufficient selection of controls in the selection domain and non-response rate in the exposure domain. Overall, most studies had relatively high scores on using NOS that varied from 5 to 7 points. However, potential confounding factors may exist regarding selection and exposure. In terms of study design and anatomic location of trauma, there was substantial heterogeneity across the studies (Table 1).
NOS, Newcastle-Ottawa scale; NRS, non-randomized study; ⋆, The study has met the criteria for a domain of the Newcastle-Ottawa Scale.

Subgroup Analysis
Subgroup analysis showed a significant difference in the conversion rate when the publication year of the study was used as a moderator (Table 3) (test for subgroup difference: p < 0.01). However, the type of injured organ was not a significant moderator. Subgroup analysis for morbidity and mortality showed that there was no significant difference in terms of publication year and injured organ.

Subgroup Analysis
Subgroup analysis showed a significant difference in the conversion rate when the publication year of the study was used as a moderator (Table 3) (test for subgroup difference: p < 0.01). However, the type of injured organ was not a significant moderator. Subgroup analysis for morbidity and mortality showed that there was no significant difference in terms of publication year and injured organ.

Discussion
Our meta-analysis suggests the favorable outcomes of laparoscopy for BAT. We found several clinically important features of laparoscopy. First, similar to the non-trauma field, our meta-analysis showed that laparoscopy had advantages in terms of blood loss during surgery and hospital stay compared to laparotomy. Second, laparoscopy in BAT compared to PAT had a higher morbidity and conversion rate. Third, the overall prevalence of missed injury, nontherapeutic laparotomy, morbidity, and mortality was very low and acceptable in BAT rather than PAT. Fourth, the conversion rate in recent studies improved more than that in previous studies. Finally, in the eligible studies included in our analysis, laparoscopy was limited to patients without hemodynamic instability or extensive trauma. Despite the substantial heterogeneity and risk of bias, our study has significant implication to trauma surgeons.
Several previous systematic reviews and meta-analyses have been conducted on laparoscopy for patients with trauma. In a systematic review and meta-analysis regarding laparoscopy in PAT [2] including 13 prospective and 38 retrospective studies, few therapeutic laparoscopies were included (13.8%). This review noted that laparoscopy had an important role in detecting and treating diaphragmatic injuries. Remarkably, the authors noted 83 missed injuries, indicating 66.7-100% sensitivity and 33-100% specificity. The eligible studies of the present meta-analysis reported only one missed injury. When operating on patients with trauma, it is crucial that injuries are not missed. The most recent systematic review and meta-analysis including 9817 laparotomies [4] demonstrated that the incidence of therapeutic laparotomy decreased from 69% to 47.5%, whereas the incidence of therapeutic laparoscopy increased from 7.2% to 22.7%. This review did not separate the outcomes of blunt trauma. In another meta-analysis that compared laparoscopy and laparotomy [28], it was reported that laparoscopy improved perioperative outcomes and reduced the risk of complications among hemodynamically stable patients with abdominal trauma. This analysis also did not separate the outcomes of blunt trauma and included many Chinese-written articles from a Chinese database. We did not include the Chinese database. To the best of our knowledge, our analysis is the first meta-analysis that analyzed the efficacy of laparoscopy for BAT. We also computed the pooled prevalence, and this significantly differed from previous studies [2,4,28].
Currently, laparoscopic surgery is widely accepted as a treatment for non-traumatic disease, and the controversy surrounding its technical issues has reduced. There have been considerable improvements in laparoscopic skill and laparoscopic equipment over the past few decades. This evolution was possible because of the development of various useful instruments, including high-resolution cameras, suturing devices, staplers, and energy devices, that allow for effective hemostasis and resection. In the subgroup analysis of our study, recent studies showed lesser conversion rate than early studies. In our study, several studies published at an early stage used laparoscopy for only diagnostic purposes [6][7][8]. However, recent studies are more in the realm of therapeutic laparoscopy, contributing to decreasing conversion rate. They included laparoscopic procedures such as bowel resection, bowel repair, bladder repair, splenectomy, distal pancreatectomy, diaphragm repair, and hemostasis [15,16,18,20,21,23]. In early studies, laparotomy was needed for these procedures. Large-scale randomized controlled trials have shown that, in terms of stomach and colon cancers, the outcomes of laparoscopic surgery are similar and non-inferior to the outcomes of open surgery [29][30][31]. This implies that little progress is required to solve the technical problems associated with bowel surgery. However, laparoscopic surgery on retroperitoneal organs, such as the duodenum and pancreas, remains controversial. No randomized controlled trials were reported in recent meta-analyses on pancreatic laparoscopic surgery [32,33]. In our analysis, no randomized controlled trials were found, and the bowel and mesentery were the most injured organs. The laparoscopic retroperitoneal approach requires greater experience and skill than the other approaches in bowel surgery. Thus, trauma surgeons need a great deal of experience and advanced skill. The possibility of open conversion may be high in severe bleeding and retroperitoneal organ injury [1]. Computed tomography (CT) or focused assessment with sonography for trauma (FAST) may help to decide to attempt therapeutic laparoscopy [1,34]. If there are no specific findings on physical examination and there is no severe bleeding in CT or FAST, therapeutic laparoscopy may be attempted. Recently, interventional radiology has evolved considerably for hemostasis in patients with hemorrhagic pelvic fracture, liver laceration, spleen rupture, or major vascular trauma [35][36][37][38].
Our analysis had several limitations. First, all the eligible studies were retrospective and observational; therefore, selection bias was inevitable. A prospective study is needed to determine the true effect size. Second, verification of publication bias was difficult because of the limited number of eligible studies. Third, we computed estimated prevalence by using single descriptive statistics because there were limited comparative studies. This may induce substantial heterogeneity. To overcome the weakness, we conducted subgroup analysis and sensitivity analysis. Fourth, only articles written in English were included. Fifth, we could not separate the effect size related to hemodynamic status even though hemodynamic stability is important for choosing the operative strategy. Finally, lower ISS in the laparoscopy group might be a confounder related to other effect sizes. The small number of studies including comparison of ISS is another limitation. However, lower ISS of the laparoscopy group in our study suggests that appropriate patient selection is crucial.

Conclusions
Laparoscopy for BAT showed favorable outcomes in terms of blood loss during surgery, hospital stay, missed injury, nontherapeutic laparotomy, and morbidity. The conversion rate has improved in recent studies. This meta-analysis suggests that laparoscopy is a safe and feasible option for BAT with hemodynamic stability. However, the retrospective nature and heterogeneity between studies make the generalization of the results of this meta-analysis limited. A large-scale multicenter prospective study is needed to determine the exact effect sizes of laparoscopy in BAT. However, such research design will be a big challenge in clinical practice.