Introduction High-Flow Nasal Therapy (HFNT) is an innovative non-invasive form of respiratory support. Compared to standard oxygen therapy (SOT), there is an equipoise regarding the effect of HFNT on patient-centred outcomes among those at high risk of developing postoperative pulmonary complications after undergoing cardiac surgery. The NOTACS trial aims to determine the clinical and cost-effectiveness of HFNT compared to SOT within 90 days of surgery in the United Kingdom, Australia, and New Zealand. This protocol describes the methods and analyses planned for economic evaluation embedded within the ongoing NOTACS trial.   Methods and analysis The economic evaluation will identify, measure and value resources and health outcomes in both trial arms and compare changes in costs with ‘days alive and at home’ and EQ-5D-5L quality adjusted life years (QALYs) from the perspective most relevant to the decision-making country. Results from pooling data across the trial will use health and social care sector perspective. All patient-specific data including hospital/community care and health outcomes will be collected prospectively. Unit costs will be sourced from national, published or local data. Missing data will be assessed, with values replaced depending on assumed mechanism of missingness, and impact of replacement on cost-effectiveness assessed. Costs and outcomes by trial arm will be presented as components and totals per patient using a range of descriptive statistics. Regression models for costs and effects will account for patient characteristics, quality of life and health service utilization at baseline. Uncertainty in parameters, sampling and heterogeneity will be addressed through deterministic, probabilistic and subgroup analyses to assess the impact of varying methods and assumptions for costs, outcomes and approaches used in base-case analysis. Results will be interpreted using recommended national cost-effectiveness thresholds.     Registration details The study is registered with ISRCTN (ISRCTN14092678) on 13/05/2020.

The authors have declared no competing interest.

The study is registered with ISRCTN (ISRCTN14092678) on 13/05/2020

https://trialsjournal.biomedcentral.com/articles/10.1186/s13063-022-06180-5

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I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The study received ethics approval in the United Kingdom from Yorkshire & The Humber- Leeds West Research Ethics Committee, Newcastle upon Tyne, UK on 2nd April 2020 (REC ref: 20/YH/0133). In Australia, the approval was obtained from South Metropolitan Health Service Human Research Ethics Committee, MURDOCH, Western Australia on 3rd September 2021 (ref: RGS0000004935) and 19th May 2022 (Ref: RGS0000005326), from St John of God Health Care Human Research Ethics Committee (ref: 1870) on 13th October 2021, and West Australian Aboriginal Health Ethics Committee (ref: HREC1146) on 29th April 2022. In New Zealand, the approval was obtained from Health and Disability Ethics Committees, Wellington, New Zealand on 12 October 2021 (ref: 21/STH/213). Written informed consent will be obtained from all participants. The results will be published in peer reviewed journals and presented at scientific conferences to inform stakeholders.

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No datasets were generated or analysed during the current study. All relevant data from this study will be made available upon study completion.