Patterns of use of e-cigarettes and their respiratory effects: protocol for an umbrella review (Preprint)

BACKGROUND Electronic nicotine delivery systems (ENDS) – e-cigarettes or vapes – have been shown to substantially reduce or eliminate many toxins compared to cigarette smoke and simultaneously ENDS use produces its own unique toxins. Yet the patterns of use among people who use ENDS are not homogeneous. Some people who use ENDS also smoke cigarettes – dual use. Other people who formerly smoked cigarettes are completely substituting ENDS – exclusive use. A small number of people who have never smoked cigarettes are using ENDS – naïve use of nicotine. Each of these patterns of use results in different exposures to toxins. Unfortunately, epidemiological studies routinely group together any ENDS use regardless of other tobacco use. OBJECTIVE The primary purpose of our umbrella review is to present all the evidence available on the respiratory effects of ENDS use by adults based on their pattern of use: dual use, exclusive use, and naïve use. With each of these patterns of use, are there benefits, no changes, or harmful effects on respiratory functioning? Our objective is to provide clinicians with a detailed analysis of how different patterns of ENDS use impact respiratory functioning, and to point to the best sources of evidence. METHODS Our umbrella review is designed with the Methods for Overviews of Reviews (MOoR) framework and the PRIOR statement (Preferred Reporting Items for Overviews of Reviews). Systematic reviews published since 2019 will be searched in four databases and three grey literature sources and secondary searches conducted with citation chasing, references lists, and referrals from respiratory specialists. Included systematic reviews will be assessed for quality with the AMSTAR2 checklist (A MeaSurement Tool to Assess Systematic Reviews). Reporting biases will be documented in three areas: unreported deviations from protocol, reporting biases drawn from the Oxford Catalogue of Bias, and internal data reporting discrepancies within the systematic review. The search processes and quality assessments will be conducted independently by two reviewers. RESULTS The search processes and results will be displayed in a PRIOR flow diagram. The systematic reviews will be reported with a study table, a second table will display their AMSTAR2 scoring and rating, and a third table will record reporting biases. A citation matrix will list all the primary studies included in the systematic reviews. Analyses will be presented based on the pattern of use: dual use, exclusive use, and naïve use. Sub-group analyses are planned for populations with asthma or COPD (Chronic Obstructive Pulmonary Disease). Our analysis will be performed with the systematic reviews rated at moderate or high confidence. The method will be a Vote Counting Direction of Effect to accommodate the expected substantial heterogeneity in the data. This analysis will indicate if ENDS use is beneficial, detrimental, or has no effect on respiratory functions based on the pattern of use. CONCLUSIONS We believe that a fair-handed and comprehensive assessment of the evidence will bring clarity to the contentious debate over the respiratory effects of ENDS by linking their effects to specific patterns of use, in particular the risks occurring from continuing cigarette smoking. CLINICALTRIAL PROSPERO CRD42024540034