Data will be analysed on an intention-to-treat basis. Demographical data will be summarised and expressed using appropriate measures of central tendency and dispersion for continuous data and frequency for categorical data. Inferential testing will be two-sided, and p<0.05 will be considered statistically significant.

Major P-NCD at 3 months will be compared between groups using the χ2 test. In the unlikely event that randomisation was not able to reduce bias by balancing out confounders, we will assess for confounding factors. This will be carried out by assessing each potential confounder individually in relation to the key predictor (DEX) and determining if the potential confounder impacts the parameter estimate of DEX using the 10% change in estimate approach. The potential confounder would also need to be significantly related to the outcome (major P-NCD). Should any confounders exist, they will be included in a logistic regression analysis.

Analysis of secondary outcomes will be considered exploratory in nature; therefore, no adjustments for multiple comparisons will be made. Categorical outcomes (delirium, death, haemodynamic instability and depression/chronic pain/mild P-NCD at 3 months) will be compared using χ2 test (Fisher’s exact test where appropriate). Continuous outcomes (LOS, opioid use and QoR-40) will first be analysed with the Shapiro-Wilk test and visually to assess for normality. If approximately normal, the independent sample t test will be used. Otherwise, the Mann-Whitney U test will be employed.

The secondary analysis will also include an analysis of the entire sample population and employ Cox proportional hazards to estimate the effect of mild P-NCD (MCI), DEX, gender, age, highest level of education, chronic inflammatory state, CNS disease (eg, previous CVA, multiple sclerosis and Parkinson’s) and postoperative delirium on the risk of developing major P-NCD at 3 months and 1 year. Missing data will be addressed using multiple imputation (or inverse probability weighting).

Two interim analyses are planned at 800 and 1600 participants. Futility will be assessed at the interim analyses using the O’Brien-Flemming stopping boundaries. Inferential statistical testing on collected outcomes will not be performed after the pilot trial to allow for its transfer to the full trial.

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