Introduction

In recent decades, laparoscopy has become the first-choice surgical approach in the treatment of many gynecological conditions [1]. Compared to open surgery, it is associated with a significant reduction in pain and postoperative infections, a shorter hospital stay, and a faster convalescence [2]. At the same time, laparoscopy has proven to be a safe and effective surgical method, with a rate of complications at the moment of the first trocar entry of about 1% [3]. Interestingly, almost half of the complications reported in the literature occur during the creation of the pneumoperitoneum [4]. This percentage has not changed over the years, although new techniques and tools have been progressively introduced [1, 5].

Complications of the closed-entry technique were commonly classified into two groups: major complications were defined as those requiring reintervention or conversion to an open procedure such as vascular and bowel injuries or solid organ laceration and bleeding, while minor complications were defined as those didn’t prolong the postoperative length of hospital stay [6-9].

Nowadays, there are two main closed techniques for creating pneumoperitoneum: blind Veress Needle (VN), and direct trocar insertion (DTI) [10, 11]. The DTI technique requires the advancing of the trocar with a blind twisting motion into the peritoneum after the elevation of the anterior abdominal wall with one hand or with towel clamps. If visual inspection with the camera confirms proper placement, pneumoperitoneum is established with the insufflation of a gas. VN requires the insertion and retraction of a spring-loaded needle with an external diameter of 2 mm. When the tip of the needle penetrates through tissues and enters the peritoneal cavity, the inner stylet springs forward. Then, carbon dioxide is insufflated creating a pneumoperitoneum [12].

Although some studies have shown that there are no significant differences in terms of complications between these techniques, there are still reticences in the use of direct access [13, 14]. Probably, this is due to the fear of causing vascular or intestinal damage.

In this systematic review and meta-analysis, we focused on blind VN and DTI evaluating major and minor complications related to each of these laparoscopic entry techniques.

Material and methods

We conducted this SR following the Cochrane Handbook version 6.3. This study was conducted with high methodology quality where every step of the PRISMA 2020 Checklist was carefully followed [15]. PROSPERO registration N° CRD42022361004.

Eligibility criteria, information sources, and search strategy

The search strategy comprised the following electronic databases: PubMed, MEDLINE, Embase, Scopus, EBSCO, Google Scholar, and ClinicalTrials.gov. The literature search was constructed until April 01, 2022, around search terms for “Veress,” “direct trocar,” “needle,” “insertion,” and “laparoscopic ways of entry.” Additional reference lists of identified original articles or reviews were searched manually.

We included both randomized controlled trials (RCTs) and observational studies. Studies in control interventions that compared VN with DTI in terms of major and minor complications and time required to access the first trocar were all considered eligible. No restrictions regarding the study period, surgery type, age, BMI, or comorbidities were applied. All the trials compared VN with DTI in a patient who underwent laparoscopic surgery. We used the Rayyan online software (www.rayyan.com) to expedite the title/abstract and full-text screening phases and to eliminate duplicate records [16].

Two reviewers (TC and RA) independently screened the title and abstract of all papers and, according to their judgment, obtained full-text reports. A conflict of reviewers’ decision on the inclusion or exclusion of any study was discussed with a third reviewer (DM) until a consensus was reached.

Data extraction

Data on design, participants, interventions, and outcomes were extracted by two reviewers (TC and RA) independently. A consensus among all authors resolved any disagreement regarding papers to be included in the analysis.

Assessment of risk of bias

Two reviewers (TC and RA) independently performed the risk of bias assessment in each study using the Risk of Bias tool for non-randomized studies of Interventions (ROBINS-I) tool for the observational studies and the RoB 2 tool for RCTs [17]. A “low risk” judgment defines a study that uses a valid methodological approach, “some concerns” defines studies susceptible to some bias, while a “high risk” judgment indicates significant bias that may invalidate the conclusions (Appendix).

Data synthesis

Statistical analysis was performed using Cochrane Review Manager version 5 software. For categorical data, we related the number reporting an event to the number at risk in each group to derive a relative odds ratio (OR) and 95% confidence interval. The continuous variable -time required to achieve complete insufflation- was presented as 95% confidence intervals (CI) of mean difference (MD) or standard mean difference (SMD). In a systematic review, heterogeneity may be defined as any kind of variability among studies. There are three different types of heterogeneity in meta-analysis: clinical heterogeneity which describes variability in the participants, interventions, and outcomes studied; methodological diversity that defines variability in study design and risk of bias; and statistical heterogeneity that refers to variability in the intervention effects being evaluated in the different studies. Heterogeneity was analyzed using the I2 statistics, one of the most commonly used heterogeneity measures that provides an estimate of the proportion of variability in a meta-analysis that is explained by differences between the included studies rather than by sampling error. The level of heterogeneity was classified as low when I2 < 25%, moderate when I2 = 25–49%, substantial when I2 > 50%. In our analysis, I2 statistics was low, revealing that there were very little variations between trials. However, we used the DerSimonian-Laird random effects model as a conservative approach to account for different sources of heterogeneity among studies.

When we identified substantial heterogeneity, we examined clinical and methodological differences between studies, and we took any statistical heterogeneity into account when interpreting the results. We found that the included studies were conducted with similar clinical approaches and statistical methods.

When we suspected methodological heterogeneity, we investigated differences in clinical factors between studies and we performed a sensitivity analysis for outcomes which included studies that selected bariatric patients with BMI > 35.

Results

Study selection

The number of records identified and the reasons for exclusion are summarized in the PRISMA flow diagram (Fig. 1).

Fig. 1
figure 1

PRISMA study flow diagram. Literature search and screening process

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We included studies with the following inclusion criteria: (1) studies comparing the efficacy and safety of direct trocar insertion and Veress needle in laparoscopic surgery in terms of major and minor complications; (2) studies enrolling patients undergoing laparoscopic surgery including gynecological, urological, bariatric and general type surgery; (3) studies reporting complete data about the outcomes of interest. We did not include case reports, case series, reviews, meta-analysis, unpublished studies, and studies with incomplete data.

We also excluded studies comparing VN or DTI with other laparoscopic entry techniques. The main outcomes were major complications (major vessel injuries, bowel injuries, port site hernia) and time required to access the first trocar. Secondary outcomes were minor complications (omental bleeding, omental emphysema, subcutaneous emphysema, extraperitoneal insufflation, multiple trocar insertions, trocar site bleeding, trocar site infection).

The literature search totaled 543 articles. In all, 470 records were excluded because they were duplicated or did not meet all predefined inclusion criteria. Full-text articles were screened for eligibility. Twelve were excluded because they presented data about minor and major complications without differentiating them in terms of a single complication [18, 19]. Twenty-one articles with a total of 9214 participants were included in the SR and in the meta-analysis.

Study characteristics

The baseline characteristics, namely, the author, year, country, and number of participants in the control and experiment group of the 21 included studies are shown in Table 1.

Table 1 Characteristics of included studies
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According to inclusion and exclusion criteria, we included studies containing participants who underwent laparoscopic surgery with the two laparoscopic techniques, VN and DTI (Fig. 1). The present analysis included a total sample of 9214 patients (Table 2).

Table 2 Outcomes and included studies
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The 21 included studies comprised 16 RCTs and 5 observational studies where the only criterion for the technique selection was the surgeon’s preference. They were performed in 9 countries: 4 in the USA [20-23], 5 in Turkey [24-28], 2 in Italy [29, 30], 2 in India [31, 32], 2 in Pakistan [33, 34], 1 in Spain [35], 1 in Iran [36], 1 in Egypt [37], 1 in Mexico [38], 1 in the Netherlands [39], and 1 in Nigeria [40].

Risk of bias of included studies

All studies had some risk of bias, as assessed by the Risk of Bias Assessment tool for Nonrandomized Studies (Robins I) and the Cochrane risk-of-bias tool for randomized trials (RoB 2). Due to the nature of the intervention, none of the RCTs were blinded; moreover, little information was given about the process of randomization and allocation concealment. (Supplementary Material Figs. 1–2). Funnel plots showed that no clear evidence of publication bias was noted (Supplementary Material Fig. 3). Review Manager 5 software was used to build a visual bias graph and summary.

The risk of publication bias was evaluated for each meta-analysis and funnel plots were generated using Review Manager 5 software. A symmetrical funnel plot signifies no evidence of a high risk of publication bias.

Synthesis of results

Bowel injuries

There were 11 studies reporting results for the proportion of patients with bowel injuries.[20-22, 26, 28-30, 32, 35, 36, 40]. Of the 11 studies reporting this outcome, 4 studies found no cases either in the VN group and the DTI group [21, 22, 32, 40]. According to the results of the present meta-analysis from random-effects model, no significant differences were found between the two groups (OR = 0.76, 95% CI: 0.24–2.36, P = 0.63, Fig. 2A).

Fig. 2
figure 2

Meta-analysis of Major complications. A Forest plot of comparison: Comparison Between Direct Trocar Insertion (DTI) and Veress needle (VN) in laparoscopic surgery, outcome: bowel injuries. B Forest plot of comparison: comparison between direct trocar insertion (DTI) and Veress needle (VN) in laparoscopic surgery, outcome: major vascular injuries. C Forest plot of comparison: comparison between direct trocar insertion (DTI) and Veress needle (VN) in laparoscopic surgery, outcome: port site hernia

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Low heterogeneity was observed between the studies (I2 = 0%). When we performed a sensitivity analysis excluding studies that selected obese participants, this finding did not change substantially (OR = 0.86, 95% CI: 0.29–2.57, P = 0.79). In the subgroup analysis containing only RCTs, we exclude two observational studies [35, 36], but we found similar results (OR = 0.87, 95% CI: 0.21–3.64, P = 0.84).

Major vascular injuries

There were 14 studies reporting results for major vascular injuries [21-24, 26-30, 32, 34-36, 40]. No vascular lesion occurred in 7 studies [21-23, 29, 30, 32, 34].

The random-effects model was used for the pooled analysis. No significant differences were found between the two groups (OR = 1.74, 95% CI 0.56–5.38, P = 0.34, Fig. 2B). After the removal of studies that included patients who underwent bariatric surgery in a sensitivity analysis, the difference between DTI and VN remains statistically insignificant (OR = 2.22, 95% CI: 0.67–7.40, P = 0.19). We also performed a subgroup analysis considering RCTs only (OR = 2.02, 95% CI: 0.32–12.86, P = 0.46).

Port site hernia

Of the 4 studies [23, 32, 34, 36] reporting data about port site hernia, in 2 studies [32, 34] no cases with either VN or DTI entry techniques occurred. No differences were observed in terms of port site hernia between the two groups (OR = 2.41, 95% CI: 0.28–20.71, P = 0.42, Fig. 2C). Heterogeneity was absent (I2 = 0%), a random-effects model was applied. Data were insufficient to perform any sensitivity analysis.

Omental bleeding

Data about omental bleeding were available from 7 studies [20, 21, 24, 26, 30, 32, 40]; no cases in both groups were encountered in 1 of the 7 studies [40]. The meta-analytic effect was statistically significant showing that the DTI group had a lower risk of omental bleeding compared to the VN group (OR = 2.32, 95% CI: 1.18–4.55, P = 0.01, Fig. 3A). The random-effects model was used although the low heterogeneity between the studies (I2 = 2%). After the removal of studies that included patients who underwent bariatric surgery in a sensitivity analysis, this finding did not change substantially (OR = 2.33, 95% CI: 1.00–5.42, P = 0.05, I2 = 21%).

Fig. 3
figure 3

Meta-analysis of minor complications (1). A Forest plot of comparison: comparison between direct trocar insertion (DTI) and Veress needle (VN) in laparoscopic surgery, outcome: omental bleeding. B Forest plot of comparison: comparison between direct trocar insertion (DTI) and Veress needle (VN) in laparoscopic surgery, outcome: omental emphysema. C Forest plot of comparison: comparison between direct trocar insertion (DTI) and Veress needle (VN) in laparoscopic surgery, outcome: subcutaneous emphysema

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Omental emphysema

According to the results of the present meta-analysis from the random-effects model, the DTI group had a lower risk of omental emphysema compared to the VN group (OR = 18.41, 95% CI: 7. 01–48.34, P < 0.00001, I2 = 0%, Fig. 3B). Data were insufficient to perform any sensitivity analysis.

Subcutaneous emphysema

There were 10 studies reporting results for subcutaneous emphysema defined as findings of gas within subcutaneous soft tissue [21, 24, 25, 27-29, 31, 32, 35, 36]. As shown in Fig. 3C, the pooled result from the random-effect model showed that the Veress needle was associated with an increased risk of subcutaneous emphysema compared with DTI (OR = 5.19, 95% CI: 2.27–11.87, P < 0.0001). We also performed a sub-group analysis after the removal of four observational studies and we found that the difference between DTI and VN remains statistically significant (OR = 6.60, 95% CI: 2.45–17.74, P = 0.0002) [24, 27, 34, 35].

Extraperitoneal insufflation

There were 9 studies reporting results for extraperitoneal insufflation [27-30, 32, 34, 37, 38, 40]. The random-effects model was used because of the moderate heterogeneity between the studies (I2 = 63%). As shown in Fig. 4A, the pooled result from the random-effects model showed that the Veress needle was associated with an increased risk of extraperitoneal insufflation compared with DTI (OR = 5.93, 95% CI: 1.69–20.87, P = 0.006). The subgroup analysis considering RCTs only showed similar statistically significantly different between the two groups (OR = 6.93, 95% CI: 1.42–33.76, P = 0.02).

Fig. 4
figure 4

Meta-analysis of minor complications (2). A Forest plot of comparison: Comparison Between Direct Trocar Insertion (DTI) and Veress needle (VN) in Laparoscopic surgery, outcome: extraperitoneal insufflation. B Forest plot of comparison: comparison between direct trocar insertion (DTI) and Veress needle (VN) in laparoscopic surgery, outcome: trocar site bleeding. C Forest plot of comparison: comparison between direct trocar insertion (DTI) and Veress needle (VN) in laparoscopic surgery, outcome: trocar site infection

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Trocar site bleeding

The pooled results from the random-effects model showed that there was no significant difference in the incidence of trocar site bleeding between the VN group and the DTI group (OR = 0.66, 95% CI, 0.25–1.79, P = 0.42). Heterogeneity between the studies was statistically insignificant (I2 = 0%). (Fig. 4B). We performed sensitivity analysis after the removal of studies that included bariatric patients, we found that results remained similar to the main analysis (OR = 0.86, 95% CI, 0.27–2.41, P = 0.69).

Trocar site infection

The pooled results from the random-effects model showed that there was no significant difference in the incidence of trocar site infection between the VN group and the DTI group (OR = 1.19, 95% CI, 0.34–4.20, P = 0.78) (Fig. 4C). We also performed a subgroup analysis considering RCTs only. We excluded the study by Jacobson et al.; however, the difference between the two groups remained statistically insignificant (OR = 1.33, 95% CI: 0.28–6.39, P = 0.72).

Multiple trocar insertions

The pooled results from the random-effects model showed that VN was associated with a higher number of attempts compared with DTI (OR = 2.27 95% CI: 1.17–4.39, P = 0.01) (Fig. 5A). When we performed a sensitivity analysis excluding studies that selected obese participants, this finding did not change substantially (OR = 2.25, 95% CI: 1.05–4.81, P = 0.04).

Fig. 5
figure 5

Meta-analysis, secondary outcomes. A Forest plot of comparison: comparison between direct trocar insertion (DTI) and Veress needle (VN) in laparoscopic surgery, outcome: multiple trocar insertions. B Forest plot of comparison: comparison between direct trocar insertion (DTI) and Veress needle (VN) in laparoscopic surgery, outcome: time required to access the first trocar (seconds from incision to 15 mmHg pneumoperitoneum)

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Time required to achieve complete insufflation

Data about the time required to achieve complete insufflation (seconds from incision to 15 mmHg pneumoperitoneum) were available from 7 studies [20, 26, 30, 34, 37, 39, 40]. No differences were observed in terms of seconds from incision to 15 mmHg pneumoperitoneum between the two groups (MD =  − 15.53, 95% CI: − 91.32 to 60.27, P = 0.69, Fig. 5B). The random-effects model was used because of the substantial heterogeneity between the studies (I2 = 96%). The sensitivity analysis after the exclusion of bariatric patients generated similar results to the main analysis (P = 0.49).

Discussion

Principal findings

According to the results of the current meta-analysis, there were no significant differences in the risk of major complications during the access manoeuvres between DTI and VN. DTI has a lower risk of minor complications such as subcutaneous emphysema, extraperitoneal insufflation, omental emphysema and omental bleeding, lower number of unsuccessful entry, or insufflation attempts. No significant differences were found between the two groups in terms of time required to access the first trocar (seconds from incision to 15 mmHg pneumoperitoneum). Thus, DTI is most likely a comparatively safe intervention in laparoscopic surgery. Heterogeneity between the included studies ranges from low to moderate. Estimation bias remained small or moderate under most circumstances.

Comparison with existing literature

Several studies, both observational and RCTs, have been published on the safety of the DTI entry technique reporting lower incidence of complications commonly related to the use of VN such as failed pneumoperitoneum, extraperitoneal insufflation, bowel insufflation, or CO2 embolism. However, the incidence was insufficient to support one of these two closed-entry techniques and no clear consensus has been reached among laparoscopic surgeons on the safest method of laparoscopic blind way of entry. Current guidelines do not support the use of a specific technique over another [41, 42].

As found in a review published in 2016 by Cornette et al., we found a higher incidence of minor complications and failed attempts using the VN method when compared to the DTI entry technique [12]. In a recent SR and meta-analysis by Marchand et. al including 7 RCTs, the authors found similar results to our review in terms of minor complications. The rate of extraperitoneal insufflation was found to be higher in the Veress needle entry group compared with the direct access entry group (OR = 0.177, 95% Cl: 0.094–0.333, P < 0.001) [43]. Similarly, in a recent systematic review and meta-analysis of the Cochrane Database including 12 RCTs with a total of 4704 participants, Ahmad et al. found a lower incidence of both extraperitoneal insufflation and omental injuries in the DTI group [10]. However, for major complications, the authors concluded that evidence was insufficient to show a difference in rates of vascular injuries, visceral injuries, or solid organ injuries when DTI was compared with VN entry [10, 12].

In our study, we included 16 RCTs and 5 prospective studies with a total of 9214 participants. We performed a subgroup analysis based on the different types of major complications increasing the pool of the included study with recent literature [32, 35, 40].

Contrary to these previous reviews, we found no significant difference between the two groups in terms of major vascular injuries (OR = 1.74, 95% CI 0.56–5.38, P = 0.34) and bowel injuries (OR = 0.76, 95% CI: 0.24–2.36, P = 0.63). However, it is important to note the rate of major vascular injury was low in these studies, with no case of vascular injury reported in 7 of the 14 studies [21-23, 29, 30, 32, 34].

Patient’s characteristic of many included studies was based on a population that was never submitted to abdominal surgery and did not include obese patients. On the other hand, other studies did not fix any exclusion criteria. Then, a previous midline laparotomy is associated with a high risk of intra-peritoneal adhesions to the parietal scar [44-46], with a higher insufflation and first trocar insertion failure rate [46,47] and a higher risk of complications [48]. In our SR only 12 of 21 studies have excluded patients with a history of midline laparotomy (Table 1).

Since obese patients and patients with a history of abdominal operations are usually associated with higher morbidity, this should be considered an influencing factor in the current study.

Extreme thinness (BMI < 18.5 kg/m2) and overweight or obesity (BMI > 25 kg/ m2) have an important influence on the difficulty of accessing manoeuvres to the abdominal cavity, both in VN and DTI techniques [49]. Patients with BMI < 18.5 kg/m2 are more likely to have vascular injuries in large vessels since the distance between the skin and the aorta is below 2.5 cm [50]. On the other hand, in patients with BMI > 25 kg/ m2, the distance between the skin and the peritoneum is about 6 cm, so the insufflation with VN requires a vertical entry of the needle to reach the cavity, and it is crucial not to produce emphysema or failed entry attempts [9, 49, 51]. However, in RCT involving around 100 women with BMI > 25 kg/m2, VN insufflation via the trans-umbilical route was compared with insufflation via the trans-uterine route. Results showed that there was no statistically significant difference in terms of complications or in terms of failure attempt to obtain pneumoperitoneum [51, 52].

In the study of Ertrugul et al., 81 bariatric patients with BMI > 40 kg/m2 or BMI of 35–40 kg/m2 with comorbidities related to obesity were enrolled [26]. Results showed no significant difference in terms of major complications and omental injuries between the two groups using the closed technique.

This updated meta-analysis confirms that there is no statistically significant safety-related difference between DTI and VN insertion techniques. According to the Royal Australian and New Zealand College of Obstetrics and Gynecology (RANZCOG) and the Society of Obstetricians and Gynecologists of Canada (SOCG) clinical practice guideline of 2020 [41, 42] for those surgeons who feel comfortable with the VN entry technique and are not familiar with the DTI approach, it is not recommended for them to change their approach based on the results of the present literature. Instead, it is suggested to choose the best-dominated type of entry at the time of the intervention, that is the entry approach that the surgeon has been trained in and is familiar with. As explained by Cuss et al., this current recommendation reflects the fact that the present evidence regarding laparoscopic entry is good as it gets because it is unlikely that appropriately powered comparative studies could be performed [1]. In agreement with this limitation, we corroborate the findings that VN is a safe method of entry, even if it still involves three blind steps, while the DTI technique only involves one blind step. On the other hand, DTI is associated with fewer insufflation complications and failed entries. However, consistent with the conclusion of Ahmad et al., we agree that more RCTs with obese and non-obese populations are needed because of the low number of major complications in the available studies [10].

Strengths and limitations

The main limitation of the present systematic review and meta-analysis is the different grades of difficulty for the operations, lack of restrictions regarding surgery type, body mass index (BMI), different experiences of the surgeons, and history of previous surgery. In addition, for many RCTs, we found that many studies did not report sufficient information about the process of randomization and the risk of biases. We decided to include also recent observational studies; however, when applicable, we performed a sub-group analysis containing only RCTs. Despite these limitations, to our knowledge, only one Cochrane review assessing the laparoscopic entry technique was recently performed (2019), our updated systematic review and meta-analyses cover a longer time interval and contain a larger number of recent randomized control trials. Furthermore, strengths include also low heterogeneity of the included studies, comprehensive search strategy, use of two reviewers to perform the literature search, data extraction, and the analysis of the risk of bias.

Conclusions

This systematic review and meta-analysis demonstrate that there is no statistically significant safety-related difference between DTI and VN insertion techniques in terms of major complications. However, a lower number of minor complications were found with DTI closed-entry technique compared with Veress access. Findings from this review support present guidelines and recommendations for further RCTs to assess the safety of these two approaches in obese and non-obese populations.