Study	Reason for exclusion
Day 1996	This was a randomised controlled trial of 50 infants with pulmonary hypertension, 16 of whom were at less than 36 weeks' gestation. The definition of prematurity is not the same as that used in this review, and in any case, it is not possible to extract data that refer solely to preterm infants.
Lindwall 2005	No untreated control group was included. Short‐term randomised cross‐over trial of response to inhaled nitric oxide among infants on continuous positive airway pressure
Skimming 1997	No untreated control group was included. This was a randomised comparison of 5 ppm and 20 ppm for 15 minutes in preterm infants.