Search methods and strategy
A literature search was performed in the following databases from their inception to January 3, 2022: MEDLINE, Embase, Cochrane Central Register of Controlled Trials (CENTRAL), and Cumulative Index to Nursing and Allied Health Literature (CINAHL). A manual search of the reference lists of the review articles on this topic was conducted. Trial registrations of ClinicalTrials.gov, EU Clinical Trials Register, and Australian New Zealand Clinical Trials Registry were searched to check for ongoing trials. The literature search strategies included the following terms: population (newborn, infant or neonate and low birth weight, LBW, VLBW, ELBW or preterm, premature) and intervention (hypercapnia, carbon dioxide, CO2). The full search strategy used for MEDLINE is presented in the supplementary material (Supplemental Table A).