James Hopkins and Jane Blazeby: Development of a core outcome set for bariatric surgery

cometObesity is a growing problem in affluent parts of the world—for example, North America and Europe—where more than a quarter of the population are obese (BMI >30) and 3-5% are severely obese (BMI >40). Obesity is associated with many health problems including high blood pressure (5.5 times more likely in people who are obese), diabetes (4 times more likely), and arthritis (2 times more likely), and it leads to reduced quality of life and inactivity. Indeed, a recent UK study showed that 70% of obese patients selected for surgery could not climb three flights of stairs.

One effective treatment for severe obesity is weight-loss (bariatric) surgery. Bariatric surgery leads to a reduction in food intake, so that excessive fat stores are used up to provide the person’s daily energy requirements. There are several types of operation commonly performed, although it is not known which is best because well designed research studies comparing commonly performed procedures are lacking. One of the limitations is the variety of different outcomes reported. Currently, there are no accepted standards for measuring or defining weight loss, for recording improvements in obesity related health problems, or for measuring and reporting complications of weight-loss surgery. Surgeons often use the measure of “percentage excess weight loss,” which is difficult to interpret and other terms include, “absolute weight change,” “average post-op weight,” “change in BMI points,” or “percentage BMI loss.” These are not equivalent, and, in fact, they cannot even be directly compared with each other. This makes comparisons between studies, even for the primary outcome of weight loss, very hard to comprehend and makes it impossible to synthesise high quality evidence. Similarly, there is a lack of definitions for “resolution” of diabetes or high blood pressure and the variety of terms and definitions used to describe the complications of obesity surgery. This means that comparing outcomes of surgical techniques may be like comparing apples and raspberries without even realising it. Given this disarray, how do we know which operation is best for patients? Even for the two most commonly performed weight loss operations worldwide, laparoscopic gastric BYpass or adjustable gastric BAND surgery, we do not have reliable and comparable long term outcomes.

Identifying a core outcome set for bariatric surgery would help to solve these problems, as long as it also has agreed definitions for each outcome. Such a set would contain a mandatory list of outcomes to be measured and reported as a minimum for registries and trials of bariatric procedures, at local, national, and international levels. This would be particularly valuable in clinical trials, where core outcome sets are being proposed to improve data synthesis and reduce problems with outcome reporting bias. The COMET (Core Outcome Measurement in Effectiveness Trials) Initiative aims to facilitate this in all areas of healthcare, bringing together researchers interested in the development and application of core outcome sets (www.comet-initiative.org). A core outcome set may also be beneficial in clinical practice, because this information could be provided as a minimum for patients who are due to have a particular operation—perhaps as a “core disclosure set.”

In the UK, the BY-BAND randomised trial has begun to answer some simple questions of comparability between these two commonly performed weight loss operations.  As part of the remit of BY-BAND, we are developing BARIACT, a core outcome set for the benefits and adverse events in BARIAtric surgery clinical trials. The aim is to provide better information for patients, researchers, and healthcare professionals who will need to make difficult decisions about weight loss surgery in the future.

James Hopkins is an academic clinical lecturer in bariatric surgery at the University of Southampton and honorary surgical registrar at University Hospital Southampton.

Jane Blazeby is a professor of surgery at the University of Bristol and honorary consultant surgeon who also directs the MRC ConDuCT Hub for Trials Methodology Research.

This project is funded by the National Institute for Health Research Health Technology Assessment (NIHR HTA) programme (project number 09/127/53). The views and opinions expressed therein are those of the authors and do not necessarily reflect those of the HTA programme, NIHR, NHS, or the Department of Health.

On behalf of the BY-BAND trial management group.