Bariatric Surgery Provision in Response to the COVID-19 Pandemic: Retrospective Cohort Study of a National Registry
Conditions: COVID-19, Bariatric Surgery Candidate
Sponsor: Imperial College London

Bariatric surgery provision in response to the COVID-19 pandemic: retrospective cohort study of a 
national registry 
 
NCT05532891 
 
11th September 2022 
 
Study protocol and statistical analysis plan 
 
1. Methods 
1.1. 
Study design 
This is a nationwide cohort study, involving retrospective analysis of prospectively collected data. 
The study design, including subgroup analysis of NHS patients, was planned at the time of study 
conception, although no formal prospective analysis plan was recorded. The study has been 
retrospectively registered on ClinicalTrials.gov: https://clinicaltrials.gov/ct2/show/NCT05532891. 
 
1.2. 
Data source and study population 
The National Bariatric Surgical Registry (NBSR) is a bespoke database for the prospective collection 
of data pertaining to all patients undergoing elective bariatric surgery for weight loss in the UK. 
Emergency cases are not recorded in NBSR, and neither are revision procedures unless the aim of 
surgery is to induce further weight loss (for example, removal of gastric band for dysphagia or 
conversion of sleeve to bypass for reflux are not recorded). At each visit, demographic, perioperative 
and clinical outcome data are recorded by the health care provider. Diabetes status is recorded pre-
operatively and at each follow up visit as follows: no indication of T2DM; impaired glycaemia or diet-
controlled; oral hypoglycaemics or insulin treatment. For the purposes of analysis we grouped the 
latter two categories as ‘on treatment’.  
 
The NBSR was used to identify all patients that underwent elective bariatric surgery during the 
pandemic (one year from 1st April 2020) or prior to the pandemic (one year from 1st September 
2018). Fully-anonymised data were extracted for the purposes of analysis.  Where a variable was 
‘not recorded’ this point was excluded from analysis. For age, gender, procedure type and provider 
the records were 100% complete, for BMI at time of surgery there was 5% missing data and for 
other variables the missing value rate was 2% or lower. 
 

1.3. 
Ethics statement 
The data holder NBSR complied with local ethics guidelines. Use of this dataset for research 
purposes conformed with UK legislation and was approved by the Health Research Authority 
(17/CAG/0023). 
 
1.4. 
Study outcomes 
Outcomes recorded and compared between the two time periods included caseload, case-mix, 
provider, demographic and baseline health status of patients, and peri-operative outcomes. 
 
1.5. 
Statistical analysis 
Statistical analysis was performed using Prism 9.3.1 for MacOS (GraphPad Software, San Diego, 
USA). Chi-square, chi-square for trend or Fisher’s exact tests were used to analyse categorical or 
ordinal values. Student’s t-test was used for continuous parametric data. P<0.05 is considered 
statistically significant.