Intratracheal budesonide mixed with surfactant to increase survival free of bronchopulmonary dysplasia in extremely preterm infants: statistical analysis plan for the international, multicenter, randomized PLUSS trial
Authors: Francis Kate L , McKinlay Christopher J D , Kamlin C Omar F , Cheong Jeanie L Y , Dargaville Peter A , Dawson Jennifer A , Doyle Lex W , Jacobs Susan E , Davis Peter G , Donath Susan M , Manley Brett J 
Published: November 2023

Abstract
Background
Bronchopulmonary dysplasia (BPD), an inflammatory-mediated chronic lung disease, is common in extremely preterm infants born before 28 weeks’ gestation and is associated with an increased risk of adverse neurodevelopmental and respiratory outcomes in childhood. Effective and safe prophylactic therapies for BPD are urgently required. Systemic corticosteroids reduce rates of BPD in the short term but are associated with poorer neurodevelopmental outcomes if given to ventilated infants in the first week after birth. Intratracheal administration of corticosteroid admixed with exogenous surfactant could overcome these concerns by minimizing systemic sequelae. Several small, randomized trials have found intratracheal budesonide in a surfactant vehicle to be a promising therapy to increase survival free of BPD. The primary objective of the PLUSS trial is to determine whether intratracheal budesonide mixed with surfactant increases survival free of bronchopulmonary dysplasia (BPD) at 36 weeks’ postmenstrual age (PMA) in extremely preterm infants born before 28 weeks’ gestation.

Methods
An international, multicenter, double-blinded, randomized trial of intratracheal budesonide (a corticosteroid) mixed with surfactant for extremely preterm infants to increase survival free of BPD at 36 weeks’ postmenstrual age (PMA; primary outcome). Extremely preterm infants aged < 48 h after birth are eligible if (1) they are mechanically ventilated, or (2) they are receiving non-invasive respiratory support and there is a clinical decision to treat with surfactant. The intervention is budesonide (0.25 mg/kg) mixed with poractant alfa (200 mg/kg first intervention, 100 mg/kg if second intervention), administered intratracheally via an endotracheal tube or thin catheter. The comparator is poractant alfa alone (at the same doses). Secondary outcomes include the components of the primary outcome (death, BPD prior to or at 36 weeks’ PMA), and potential systemic side effects of corticosteroids. Longer-term outcomes will be published separately, and include cost-effectiveness, early childhood health until 2 years of age, and neurodevelopmental outcomes at 2 years of age (corrected for prematurity).

Statistical analysis plan
A sample size of 1038 infants (519 in each group) is required to provide 90% power to detect a relative increase in survival free of BPD of 20% (an absolute increase of 10%), from the anticipated event rate of 50% in the control arm to 60% in the intervention (budesonide) arm, alpha error 0.05. To allow for up to 2% of study withdrawals or losses to follow-up, PLUSS aimed to enroll a total of 1060 infants (530 in each arm). The binary primary outcome will be reported as the number and percentage of infants who were alive without BPD at 36 weeks’ PMA for each randomization group. To estimate the difference in risk (with 95% CI), between the treatment and control arms, binary regression (a generalized linear multivariable model with an identity link function and binomial distribution) will be used. Along with the primary outcome, the individual components of the primary outcome (death, and physiological BPD at 36 weeks’ PMA), will be reported by randomization group and, again, binary regression will be used to estimate the risk difference between the two treatment groups for survival and physiological BPD at 36 weeks’ PMA.