Health economics of bariatric surgery

General background: Obesity (defined as body mass index [BMI] ≥30 kg/m2) is an escalating global epidemic. Obesity poses significant health risks to the lives of affected people. Moreover, obesity imposes substantial economic burdens on individuals, healthcare payers and societies due to, for example, direct healthcare costs and numerous indirect costs including productivity losses. Among various types of surgical and non-surgical treatments, bariatric (metabolic or weight loss) surgery was found to be the most efficacious and the only long-lasting reliable option to severe and resistant obesity. Despite the clinical benefits of bariatric surgery being confirmed, the health economic impacts of bariatric surgery remain under-researched, particularly in Australia. Principal objectives: The overarching aim of this thesis was to investigate and generate health economic evidence for bariatric surgery, which could be used to populate future economic models. The specific aims of this thesis were to: 1) for the first time systematically summarize and meta-analyse the impact of bariatric surgery on utility-based quality of life (i.e., health state utilities [HSUs]) and explore the predictors of HSU changes; 2) systematically synthesise and for the first time meta-analyse all evidence regarding the economic value of bariatric surgery across the depth and breadth of the health economics literature; 3) for the first time investigate the scale, disaggregated profile, and determinants of healthcare costs associated with primary bariatric surgery within Tasmanian public health system; and 4) further investigate the critical care unit (CCU) utilisation after bariatric surgery and its relevant predictors within Tasmanian public health system; and finally 5) validate the economic impact of bariatric surgery compared with matched controls using a large population-based cohort in Australia. Methods & Main findings: To address these objectives, five papers were developed. The first paper (Chapter 3) presented a comprehensive systematic review with meta-analysis to investigate the impact of bariatric surgery on HSUs. The synthesised results suggested that HSUs increased (particularly one-year) after surgery. This study substantially overcomes the challenges associated with systematically selecting HSU data that could be used as more reliable inputs to future bariatric surgery-related cost-utility models. The second paper (Chapter 4) provided another comprehensive systematic review with meta-analysis to investigate the economic evidence of bariatric surgery. This study found that bariatric surgery is a cost-saving treatment for obesity over the life course, particularly when indirect costs were considered. Health economists therefore should consider a broad range of direct and indirect costs to evaluate the true economic impact of bariatric surgery. The third paper (Chapter 5) presented the first detailed characterisation of the scale, disaggregated profile, and determinants of bariatric-related costs, and examined the evolution of resource utilisation patterns and costs. This study complements previous exploratory findings with the disaggregated (micro-level) bariatric-related costs and their contributions over time, concluding that resource utilisation patterns and costs for bariatric are changing, which is as expected from the changing incidence of surgery type in Australia over time. Further, the micro-costing approach provides precise cost inputs that can be used in future health economic evaluations of bariatric surgery to facilitate decision making in alternative contextual settings. The fourth paper (Chapter 6) presented the first mixed-methods research to investigate CCU utilisation after bariatric surgery in Tasmanian publich healthcare system. In addition to the healthcare utilisation and cost data, this study has identified several predictors associated with planned and unplanned CCU admission. The identified risk factors could be used in the development of a risk tool or decision tree that would likely add a greater degree of precision to current clinical guidelines for allocating CCU resources for bariatric eligible patients in Australia. The fifth paper (Chapter 7) presented the first contemporary large population-based longitudinal cohort study to validate the economic impacts of bariatric surgery in an Australian population aged 45 year and over. By utilizing the linear mixed-effects model and the difference-in-differences approach to map the healthcare costs of 8 years before and 8 years after bariatric surgery, and considering an approximation of indirect costs, we found that the economic benefits of bariatric surgery increase when a longer horizon was considered, whilst cost-savings were not achieved during the study period even after the consideration of indirect costs in this middle-aged-to-elderly population sample. Future longer-term research is needed to validate our findings in younger population cohorts in Australia. Results of Chapters 4 to 7 also pointed out the strictly limited availability of bariatric surgery in Australian public healthcare system causing long wait times and other complications. This thesis highlights the need for appropriate strategies to eliminate restrictive and burdensome bariatric surgery-related preoperative requirements to relieve the prolonged wait time for bariatric surgery in public healthcare system to optimally tackle the obesity pandemic, especially in the post-COVID-19 world. Conclusions: In summary, the body of work presented in this thesis (which armed with a comprehensive structure of the statistical theories and methods) has substantially added to our understanding of the health economic impacts of bariatric surgery. Health-economic evidence is more robust for decision making process compared to the evidence solely based on clinical outcomes or economics research. The costs and HSU estimates generated from this thesis will contribute to the future bariatric surgery-related health economic evaluations. Our important recommendation for the healthcare policy makers is to devise appropriate strategies to relieve the long waitlist for bariatric surgery in public healthcare system