Brittle fracture mechanisms and toughness of model low alloy steels chemically representative of macrosegregated forgings

International audienceThe influence of the chemical composition on the brittle fracture behaviour of quenched and tempered low alloy bainitic steels was investigated thanks to the laboratory elaboration of three model alloys which have underwent a heat treatment to improve their chemical homogeneity. Two model materials with chemical compositions simulating zones of large (0.29%C) and intense (0.38%C) positive macrosegregation were characterized and compared with the nominal composition material (0.18%C). The ductile to brittle transition temperatures T56J and T0 of the materials with nominal and large carbon content are similar, whilst those of the material with the highest carbon content are unexpectedly significantly lower. Fractographic analyses indicate that the brittle fracture mechanisms depend also on the chemical composition. For 0.18 and 0.29%C, cleavage is the dominant brittle fracture mechanism, whilst a mix of cleavage and intergranular failure is observed for 0.38%C at the same levels of fracture energy or toughness. When cleavage failure is the dominant mechanism, it often originates at large molybdenum and manganese-enriched carbides located at grain boundaries likely identified as former austenitic grain ones. Microstructural analyses show variations of the large carbide population and ferritic grain size between the three alloys. Also, as carbon content increases, an evolution towards a lower bainite/martensite crystallographic microstructure is observed. The effects of these microstructural differences on the brittle fracture behavior is discussed

Revision/Conversion Surgeries After One Anastomosis Gastric Bypass-An Experts' Modified Delphi Consensus

Purpose: There is a lack of evidence for treatment of some conditions including complication management, suboptimal initial weight loss, recurrent weight gain, or worsening of a significant obesity complication after one anastomosis gastric bypass (OAGB). This study was designed to respond to the existing lack of agreement and to provide a valuable resource for clinicians by employing an expert-modified Delphi consensus method. Methods: Forty-eight recognized bariatric surgeons from 28 countries participated in the modified Delphi consensus to vote on 64 statements in two rounds. An agreement/disagreement among ≥ 70.0% of the experts was regarded to indicate a consensus. Results: A consensus was achieved for 46 statements. For recurrent weight gain or worsening of a significant obesity complication after OAGB, more than 85% of experts reached a consensus that elongation of the biliopancreatic limb (BPL) is an acceptable option and the total bowel length measurement is mandatory during BPL elongation to preserve at least 300–400 cm of common channel limb length to avoid nutritional deficiencies. Also, more than 85% of experts reached a consensus on conversion to Roux-en-Y gastric bypass (RYGB) with or without pouch downsizing as an acceptable option for the treatment of persistent bile reflux after OAGB and recommend detecting and repairing any size of hiatal hernia during conversion to RYGB. Conclusion: While the experts reached a consensus on several aspects regarding revision/conversion surgeries after OAGB, there are still lingering areas of disagreement. This highlights the importance of conducting further studies in the future to address these unresolved issues. Graphical Abstract: (Figure presented.)

Patient Selection in One Anastomosis/Mini Gastric Bypass-an Expert Modified Delphi Consensus

Purpose: One anastomosis/mini gastric bypass (OAGB/MGB) is up to date the third most performed obesity and metabolic procedure worldwide, which recently has been endorsed by ASMBS. The main criticisms are the risk of bile reflux, esophageal cancer, and malnutrition. Although IFSO has recognized this procedure, guidance is needed regarding selection criteria. To give clinicians a daily support in performing the right patient selection in OAGB/MGB, the aim of this paper is to generate clinical guidelines based on an expert modified Delphi consensus. Methods: A committee of 57 recognized bariatric surgeons from 24 countries created 69 statements. Modified Delphi consensus voting was performed in two rounds. An agreement/disagreement among ≥ 70.0% of the experts was considered to indicate a consensus. Results: Consensus was achieved for 56 statements. Remarkably, ≥ 90.0% of the experts felt that OAGB/MGB is an acceptable and suitable option "in patients with Body mass index (BMI) > 70, BMI > 60, BMI > 50 kg/m2 as a one-stage procedure," "as the second stage of a two-stage bariatric surgery after Sleeve Gastrectomy for BMI > 50 kg/m2 (instead of BPD/DS)," and "in patients with weight regain after restrictive procedures. No consensus was reached on the statement that OAGB/MGB is a suitable option in case of resistant Helicobacter pylori. This is likely as there is a concern that this procedure is associated with reflux and its related long-term complications including risk of cancer in the esophagus or stomach. Also no consensus reached on OAGB/MGB as conversional surgery in patients with GERD after restrictive procedures. Consensus for disagreement was predominantly achieved "in case of intestinal metaplasia of the stomach" (74.55%), "in patients with severe Gastro Esophageal Reflux Disease (GERD)(C,D)" (75.44%), "in patients with Barrett's metaplasia" (89.29%), and "in documented insulinoma" (89.47%). Conclusion: Patient selection in OAGB/MGB is still a point of discussion among experts. There was consensus that OAGB/MGB is a suitable option in elderly patients, patients with low BMI (30-35 kg/m2) with associated metabolic problems, and patients with BMIs more than 50 kg/m2 as one-stage procedure. OAGB/MGB can also be a safe procedure in vegetarian and vegan patients. Although OAGB/MGB can be a suitable procedure in patients with large hiatal hernia with concurrent hiatal hernia, it should not be offered to patients with grade C or D esophagitis or Barrett's metaplasia

Metabolic and Bariatric Surgeon Criteria-An International Experts' Consensus

Purpose: With the global epidemic of obesity, the importance of metabolic and bariatric surgery (MBS) is greater than ever before. Performing these surgeries requires academic training and the completion of a dedicated fellowship training program. This study aimed to develop guidelines based on expert consensus using a modified Delphi method to create the criteria for metabolic and bariatric surgeons that must be mastered before obtaining privileges to perform MBS. Methods: Eighty-nine recognized MBS surgeons from 42 countries participated in the Modified Delphi consensus to vote on 30 statements in two rounds. An agreement/disagreement among ≥ 70.0% of the experts was regarded to indicate a consensus. Results: Consensus was reached on 29 out of 30 statements. Most experts agreed that before getting privileges to perform MBS, surgeons must hold a general surgery degree and complete or have completed a dedicated fellowship training program. The experts agreed that the learning curves for the various operative procedures are approximately 25–50 operations for the LSG, 50–75 for the OAGB, and 75–100 for the RYGB. 93.1% of experts agreed that MBS surgeons should diligently record patients’ data in their National or Global database. Conclusion: MBS surgeons should have a degree in general surgery and have been enrolled in a dedicated fellowship training program with a structured curriculum. The learning curve of MBS procedures is procedure dependent. MBS surgeons must demonstrate proficiency in managing postoperative complications, collaborate within a multidisciplinary team, commit to a minimum 2-year patient follow-up, and actively engage in national and international MBS societies. Graphical Abstract: (Figure presented.