An Experimental Study of Intraluminal Hyperpressure Reproducing a Gastric Leak Following a Sleeve Gastrectomy

Experimental and numerical study of solid needle insertions into human stomach tissue

PURPOSE

Oral drug delivery is the Holy Grail in the field of drug delivery. However, poor bioavailability limits the oral intake of macromolecular drugs. Oral devices may overcome this limitation, but a knowledge gap exists on the device-tissue interaction. This study focuses on needle insertion into the human stomach experimentally and numerically. This will guide early stages of device development.

METHODS

Needle insertions were done into excised human gastric tissue with sharp and blunt needles at velocities of 0.0001 and 0.1 m/s. Parameters for constitutive models were determined from tensile visco-hyperelastic biomechanical tests. The computational setup modeled four different needle shape indentations at five velocities from 0.0001 to 5 m/s.

RESULTS

From experiments, peak forces at 0.1 and 0.0001 m/s were 0.995 ± 0.296 N and 1.281 ± 0.670 N (blunt needle) and 0.325 ± 0.235 N and 0.362 ± 0.119 N (sharp needle). The needle geometry significantly influenced peak forces (p < 0.05). A Yeoh-Prony series combination was fitted to the tensile visco-hyperelastic biomechanical data and used for the numerical model with excellent fit (R2 = 0.973). Both needle geometry and insertion velocity influenced the stress contour and displacement magnitudes as well as energy curves.

CONCLUSION

This study contributes to a better understanding of needle insertion into the stomach wall. The numerical model demonstrated agreement with experimental data providing a good approach to early device iterations. Findings in this study showed that insertion velocity and needle shape affect tissue mechanical outcomes.

Unravelling the mechanics of gastric tissue: A comparison of constitutive models, damage probability and microstructural insights

With the increasing prevalence of obesity worldwide, bariatric surgery is becoming increasingly common. However, the mechanic of the gastric wall related to bariatric surgery complications remains to be investigated. This study aims to understand mechanical behaviour of stomach by developing advanced material laws for gastric tissue incorporating microstructure. A multi-scale characterisation of the porcine stomach wall was performed in the fundus and corpus anatomical regions and in circumferential and longitudinal orientations The protocol included uniaxial tensile testing until damage, survival analysis to provide damage probability, comparison of phenomenological (Fung and Ogden order 1, 2 and 3) and structural (Holzapfel fibre-reinforced) computational models fitted to the experimental data, and quantitative analysis of elastin and collagen fibre structure from histological slides. All constitutive models fitted the experimental data well (r2 > 0.988 and RSME<3.8 kPa). Longitudinal and circumferential elastic modulus in quasi linear phase were respectively 1.75 ± 1.2 MPa, 0.76 ± 0.35 MPa for fundus, and 2.30 ± 0.66 MPa, 1.36 ± 0.89 MPa for corpus, highlighting significant differences between orientations in fundus and corpus, with an overall softer fundus in the circumferential direction. Microstructure analysis illustrated collagen and elastin fibre orientation, dispersion and density. As microstructure appears to play an important role in stomach biomechanics, model incorporating fibre structure such as Holzapfel fibre-reinforced model, seem best suited to describe the material behaviour of the stomach wall. Future research should complement these findings with an expanded sample set in human models.

Regional differences in stomach stretch during organ filling and their implications on the mechanical stress response

As part of the digestive system, the stomach plays a crucial role in the health and well-being of an organism. It produces acids and performs contractions that initiate the digestive process and begin the break-up of ingested food. Therefore, its mechanical properties are of interest. This study includes a detailed investigation of strains in the porcine stomach wall during passive organ filling. In addition, the observed strains were applied to tissue samples subjected to biaxial tensile tests. The results show inhomogeneous strains during filling, which tend to be higher in the circumferential direction (antrum: 13.2%, corpus: 22.0%, fundus: 67.8%), compared to the longitudinal direction (antrum: 4.8%, corpus: 24.7%, fundus: 50.0%) at a maximum filling of 3500 ml. Consequently, the fundus region experienced the greatest strain. In the biaxial tensile experiments, the corpus region appeared to be the stiffest, reaching nominal stress values above 400 kPa in the circumferential direction, whereas the other regions only reached stress levels of below 50 kPa in both directions for the investigated stretch range. Our findings gain new insight into stomach mechanics and provide valuable data for the development and validation of computational stomach models.

Characterization of the layer, direction and time-dependent mechanical behaviour of the human oesophagus and the effects of formalin preservation

The mechanical characterization of the oesophagus is essential for applications such as medical device design, surgical simulations and tissue engineering, as well as for investigating the organ's pathophysiology. However, the material response of the oesophagus has not been established ex vivo in regard to the more complex aspects of its mechanical behaviour using fresh, human tissue: as of yet, in the literature, only the hyperelastic response of the intact wall has been studied. Therefore, in this study, the layer-dependent, anisotropic, visco-hyperelastic behaviour of the human oesophagus was investigated through various mechanical tests. For this, cyclic tests, with increasing stretch levels, were conducted on the layers of the human oesophagus in the longitudinal and circumferential directions and at two different strain rates. Additionally, stress-relaxation tests on the oesophageal layers were carried out in both directions. Overall, the results show discrete properties in each layer and direction, highlighting the importance of treating the oesophagus as a multi-layered composite material with direction-dependent behaviour. Previously, the authors conducted layer-dependent cyclic experimentation on formalin-embalmed human oesophagi. A comparison between the fresh and embalmed tissue response was carried out and revealed surprising similarities in terms of anisotropy, strain-rate dependency, stress-softening and hysteresis, with the main difference between the two preservation states being the magnitude of these properties. As formalin fixation is known to notably affect the formation of cross-links between the collagen of biological materials, the differences may reveal the influence of cross-links on the mechanical behaviour of soft tissues.

Mechanical experimentation of the gastrointestinal tract: a systematic review

The gastrointestinal (GI) organs of the human body are responsible for transporting and extracting nutrients from food and drink, as well as excreting solid waste. Biomechanical experimentation of the GI organs provides insight into the mechanisms involved in their normal physiological functions, as well as understanding of how diseases can cause disruption to these. Additionally, experimental findings form the basis of all finite element (FE) modelling of these organs, which have a wide array of applications within medicine and engineering. This systematic review summarises the experimental studies that are currently in the literature (n = 247) and outlines the areas in which experimentation is lacking, highlighting what is still required in order to more fully understand the mechanical behaviour of the GI organs. These include (i) more human data, allowing for more accurate modelling for applications within medicine, (ii) an increase in time-dependent studies, and (iii) more sophisticated in vivo testing methods which allow for both the layer- and direction-dependent characterisation of the GI organs. The findings of this review can also be used to identify experimental data for the readers' own constitutive or FE modelling as the experimental studies have been grouped in terms of organ (oesophagus, stomach, small intestine, large intestine or rectum), test condition (ex vivo or in vivo), number of directions studied (isotropic or anisotropic), species family (human, porcine, feline etc.), tissue condition (intact wall or layer-dependent) and the type of test performed (biaxial tension, inflation-extension, distension (pressure-diameter), etc.). Furthermore, the studies that investigated the time-dependent (viscoelastic) behaviour of the tissues have been presented.

Oversewing the Staple Line: Does It Safe to Prevent Leakage?

Introduction: The staple line (SL) leak remains one of the most serious complications after laparoscopic sleeve gastrectomy (LSG). The present study aims to determine whether reinforcing the SL with sutures is effective in maintaining tissue integrity. Materials and Methods: LSG Specimens of 60 patients were ex vivo studied. The specimens were divided into three groups: In group 1, the entire SL was reinforced, while the upper half part of the SL was reinforced from fundus to antrum in group 2. The SL was not reinforced in group 3. Then, the pressure inside the sample was increased, and the bursting pressure location and pressure value during the bursting were recorded. Results: The bursting pressure was significantly higher in entire and half oversewed SL groups than the none reinforced group (group 1: 115 mmHg [95-170]; group 2: 95 mmHg [80-120]; group 3: 40 mmHg [22-60], respectively, [P < .001]). The most common site of bursting was in the middle ⅓ of SL (35, 53.8%), followed by the proximal ⅓ part of SL (18, 27.7%), and the distal ⅓ part of SL (12, 18.5%), respectively. The bursting site was significantly more frequent in the corpus than the other parts of the SL (P = .013). Conclusion: Reinforcing the SL with sutures preserves tissue integrity. Although bursting was most frequently observed in the corpus region ex vivo, the fact that almost all real-life leaks develop in the area close to the Angle of His. This situation suggests that strengthening the suture line with reinforcement alone will not be protective enough against leaks in the fundus line, and factors such as tissue ischemia may be considered.

Mechanism of Staple Line Leak After Sleeve Gastrectomy via Isobaric Pressurisation Concentrating Stress Forces at the Proximal Staple Line

Purpose

Staple line leak following sleeve gastrectomy is a significant problem and has been hypothesised to be related to hyperpressurisation in the proximal stomach. There is, however, little objective evidence demonstrating how these forces could be transmitted to the luminal wall. We aimed to define conditions in the proximal stomach and simulate the transmission of stress forces in the post-operative stomach using a finite element analysis (FEA).

Materials and Methods

The manometry of fourteen patients post sleeve gastrectomy was compared to ten controls. Manometry, boundary conditions, and volumetric CT were integrated to develop six models. These models delineated luminal wall stress in the proximal stomach. Key features were then varied to establish the influence of each factor.

Results

The sleeve gastrectomy cohort had a significantly higher peak intragastric isobaric pressures 31.58 ± 2.1 vs. 13.49 ± 1.3 mmHg (p = 0.0002). Regions of stress were clustered at the staple line near the GOJ, and peak stress was observed there in 67% of models. A uniform greater curvature did not fail or concentrate stress under maximal pressurisation. Geometric variation demonstrated that a larger triangulated apex increased stress by 17% (255 kPa versus 218 kPa), with a 37% increase at the GOJ (203kPA versus 148kPA). A wider incisura reduced stress at the GOJ by 9.9% (128 kPa versus 142 kPa).

Conclusion

High pressure events can occur in the proximal stomach after sleeve gastrectomy. Simulations suggest that these events preferentially concentrate stress forces near the GOJ. This study simulates how high-pressure events could translate stress to the luminal wall and precipitate leak.

Graphical Abstract

Primary Sleeve Gastrectomy and Leaks: The Impact of Fundus-Wall Thickness and Staple Heights on Leakage-An Observational Study of 500 Patients

Introduction: The most feared complication of laparoscopic sleeve gastrectomy (LSG) is staple-line leakage. Staple height and fundus-wall thickness might influence such leakage, and this study examined their possible impact on leak incidence. Factors including gender, age, comorbidities, and reinforcement of the staple line were also investigated.

Methods: A total of 500 patients between 17 and 71 years of age who were scheduled for LSG were selected to participate in the study. For technical reasons, 53 were excluded. The fundus-wall thickness of 447 patients after LSG was investigated. The impact of staple height, fundus-wall thickness, demographic and medical factors on leak incidence were investigated. Most of our patients (309) were female (69%), while 138 were male (31%).

Results: The mean thickness of the proximal fundus wall was 2,904 μm, 3,172 μm in men and 2,784 μm in women. The leak rate was 4.9%. Age, fundus-wall thickness, and BMI showed a strong influence on leak risk, but this effect was significant only for age (p = 0.01). Patient gender and staple size showed no significant influence on the correlation between fundus-wall thickness and leak risk. Gender displayed a small effect of influence on this correlation, with η2 = 0.05.

Discussion: Because older age had a significant effect on increasing the risk of staple-line leakage, there is a need for a more specific focus on these patients. Thinner fundus wall and female gender might predispose patients to staple-line leaks, but a significant value could not be reached. Therefore, staple size should remain the surgeon's choice based on clinical experience.

A Comprehensive Review of Endoscopic Management of Sleeve Gastrectomy Leaks

BACKGROUND

Bariatric surgery leaks result in significant morbidity and mortality. Experts report variable therapeutic approaches, without uniform guidelines or consensus.

OBJECTIVE

To review the pathogenesis, risk factors, prevention, and treatment of gastric sleeve leaks, with a focus on endoscopic approaches. In addition, the efficacy and success rates of different treatment modalities are assessed.

DESIGN

A comprehensive review was conducted using a thorough literature search of 5 online electronic databases (PubMed, PubMed Central, Cochrane, EMBASE, and Web of Science) from the time of their inception through March 2020. Studies evaluating gastric sleeve leaks were included. MeSH terms related to "endoscopic," "leak," "sleeve," "gastrectomy," "anastomotic," and "bariatric" were applied to a highly sensitive search strategy. The main outcomes were epidemiology, pathophysiology, diagnosis, treatment, and outcomes.

RESULTS

Literature search yielded 2418 studies of which 438 were incorporated into the review. Shock and peritonitis necessitate early surgical intervention for leaks. Endoscopic therapies in acute and early leaks involve modalities with a focus on one of: (i) defect closure, (ii) wall diversion, or (iii) wall exclusion. Surgical revision is required if endoscopic therapies fail to control leaks after 6 months. Chronic leaks require one or more endoscopic, radiologic, or surgical approaches for fluid collection drainage to facilitate adequate healing. Success rates depend on provider and center expertise.

CONCLUSION

Endoscopic management of leaks post sleeve gastrectomy is a minimally invasive and effective alternative to surgery. Their effect may vary based on clinical presentation, timing or leak morphology, and should be tailored to the appropriate endoscopic modality of treatment.

A French National Study on Gastropleural and Gastrobronchial Fistulas After Bariatric Surgery: the Impact of Therapeutic Strategy on Healing

PURPOSE

Gastropleural and gastrobronchial fistulas (GPF/GBFs) are serious but rare complications after bariatric surgery whose management is not consensual. The aim was to establish a cohort and evaluate different clinical presentations and therapeutic options.

MATERIALS AND METHODS

A multicenter and retrospective study analyzing GPF/GBFs after bariatric surgery in France between 2007 and 2018, via a questionnaire sent to digestive and thoracic surgery departments.

RESULTS

The study included 24 patients from 9 surgical departments after initial bariatric surgery (21 sleeve gastrectomies; 3 gastric bypass) for morbid obesity (mean BMI = 42 ± 8 kg/m²). The GPF/GBFs occurred, on average, 124 days after bariatric surgery, complicating an initial post-operative gastric fistula (POGF) in 66% of cases. Endoscopic digestive treatment was performed in 79% of cases (n = 19) associated in 25% of cases (n = 6) with thoracic endoscopy. Surgical treatment was performed in 83% of cases (n = 20): thoracic surgery (n = 5), digestive surgery (n = 8), and combined surgery (n = 7). No patient died. Overall morbidity was 42%. The overall success rate of the initial and secondary strategies was 58.5% and 90%, respectively. The average healing time was approximately 7 months. Patients who had undergone thoracic surgery (n = 12) had more initial management failures (n = 9/12) than patients who had not (n = 3/12), p = 0.001.

CONCLUSION

Complex and life-threatening fistulas that are revealed late require a multidisciplinary strategy. Thoracic surgery should be reserved once the abdominal leak heals; otherwise, it is associated with a higher risk of failure.