Our systematic review has several limitations. Firstly, we developed a
classification of criteria used to define LTOT based on measures of
duration or additional criteria. Given the variability and lack of
clarity on reporting for some definitions, misclassification could have
occurred. However, we minimised misclassification by performing data
collection with two independent reviewers. Secondly, since we excluded
studies assessing LTOT in surgical settings the results and
recommendations drawn from this study may not be applicable for studies
assessing LTOT prior or post-surgery. Thirdly, we did not test the
performance of different definitions in identifying LTOT users but
rather identified those who have been tested to guide future researchers
in their choices. Fourthly, we only addressed the completeness of
reporting using core items relevant to the operationalisation of LTOT
definitions and associated results, identifying key elements that future
studies should consider to increase their transparency and
reproducibility and did not assess the methodological quality or
relevance of included studies.