Oxygen index (OI) was the primary outcome and it was measured at 1, 6 and 24 hours. Since significant drop-out was expected and we intended to look for longitudinal trend in OI over time on first day of ventilation, it was decided a priori to conduct analysis only on those infants who complete initial 24 hrs of ventilation. Moreover, the proportion of subjects who could not complete initial 24 hrs of ventilation after randomization were quite similar in both the groups (HFOV: 25.8%; SIMV: 27.3%).

As per our unit policy we administer surfactant to preterms with gestational maturity < 34 wks having respiratory distress due to HMD at earliest possible hours; however, it is used in only those who can afford it. We use Curosurf (porcine minced) for infants weighing <1000 g and Survanta (bovine minced) for those >1000 g. None of our patients in either group had received multiple doses of surfactant. Detailed analysis of patients receiving surfactant was not a stated objective; however, the major baseline characteristics were similar in both the groups. It was aimed to keep the tidal volumes lower by using lower PIP and optimal PEEP to maximally recruit lungs in synchronized intermittent mandatory ventilation (SIMV) group; however, tidal volume was not measured.