Factors influencing postoperative weight loss in bariatric surgery: standardizing perioperative care
Authors:   , Reiber Beata Myung Mi 
Published: April 2023

The aim of this dissertation was to identify both patient related - and surgical factors influencing weight loss (WL) after bariatric surgery. By doing so optimization of postoperative results and standardization of the perioperative processes were emulated. Chapter 1 provides an introduction to the topic. Chapter 2 investigates patient-related factors contributing to postoperative WL in the preoperative phase. Results demonstrated that increased preoperative weight loss is associated with increased weight loss up to three years postoperatively in patients undergoing primary LRYGB. This chapter supports the hypothesis that patient motivation to adjust to a different lifestyle postoperatively is, albeit partially, quantified through preoperative WL. Chapter 3 demonstrates that structurally creating the gastric pouch with a gastric tube as calibration, leads to 5% more total weight loss after 2 year follow up compared to creating the pouch with the carpenters eye. Chapter 4 investigates whether patients demonstrating weight regain or insufficient weight loss after primary LRYGB would benefit from resizing the gastric pouch and which was the preferred technique. The conclusion was that in selected cases sleeve resection of the pouch and gastrojejunostomy without recreating the gastrojejunostomy may be the preferred technique over the technique that does recreate the gastrojejunostomy. Chapter 5 is a systematic review and meta-analysis aiming to research the possible influence of adherence to medical follow-up (FU) on postoperative WL both short and long term after LRYGB and LSG. This resulted in a significant association between adherence to FU and percentage excess weight loss (%EWL) up to three years after surgery. However, with the scarce available literature on the longer term FU (>3 years after surgery), no influence of FU on WL was discovered. Chapter 6 is a prospective cohort study and explores the association between adherence to FU and WL in patients scheduled for 3 to 5 year individual follow-up appointments. No such association could be demonstrated. Age, persistent comorbidities and vitamin deficiencies, a yearly salary <20,000 euro, no health insurance coverage, and not understanding the importance of FU were risk factors for non adherence. It was concluded that stringent FU in its current form should be re-evaluated as FU is not associated with a higher postoperative WL. Chapter 7 is a multicenter study that concludes that the effect of adherence to group based programs on WL was very small but statistically significant, although adherence was not identified as an independent risk factor for insufficient WL in the regression analysis. Independent factors associated with a low attendance rate were younger age, male sex, and LSG. Independent factors negatively associated with %TWL were male sex, SG, and diabetes mellitus. Chapter 8 researched male patients with the hypothesis that males present later in the process of morbid obesity and consequently with more – and more severe comorbidities. This was confirmed by this retrospective cohort study and should prompt physicians to refer male patients with morbid obesity earlier in the course of the disease. Chapter 9 is a systematic review providing an extensive overview of current machine learning (ML) applications in bariatric surgery and its future perspectives. This chapter shows that ML has predominantly been used for prediction of postoperative complications and WL. However, ML algorithms have mainly been applied to datasets without external validation and large patient databases are needed to improve generalizability and allow for clinical validation. The findings of the presented studies are discussed and future perspectives are described in chapter 10.