Increased 36-Week Survival with High Oxygen Saturation Target in Extremely Preterm Infants

Following advice from the Data Monitoring Committees (DMCs), recruitment to the U.K. and Australian Benefits of Oxygen Saturation Targeting (BOOST II) trials has closed early. This decision was due to the results of a joint safety analysis that showed higher survival rates at 36 weeks' postmenstrual age (PMA) in infants born <28 weeks of gestation and randomly assigned to oxygen saturation (SpO2) targets of 91-95% rather than 85-89% while breathing supplemental oxygen.
During the SUPPORT trial, published in 2010, infants randomly assigned to the SpO2 lower target (85-89%) showed a lower risk of retinopathy of prematurity than infants in the higher target group (91-95%) (8.6% vs. 17.9%; P<0.001), but they also had a lower rate of survival to hospital discharge (mortality, 19.9% vs. 16.2%; P=0.04). The BOOST II trials were designed to compare SpO2 targets of 85-89% versus 91-95%; survival without disability at 2 years corrected for gestation was the primary outcome. In the U.K. and Australian BOOST II trials, infants have been managed with the use of oximeters similar to those used in the SUPPORT trial, but re-fitted with a revised calibration algorithm, which was associated with improved SpO2 targeting.
In December 2010, a joint safety analysis of survival at 36 weeks' PMA was undertaken, pooling 2315 infants in the U.K., Australian, and New Zealand trials with the 1316 infants in the SUPPORT trial. Among all 3631 infants, those randomly assigned to an SpO2 of 91-95% had a higher survival rate than those assigned to an SpO2 of 85-89% (mortality, 17.3% vs. 14.4%; P=0.015). Among the 1055 infants in the U.K. and Australian trials who were treated after the change in the calibration algorithm, survival differences were greater (mortality, 21.8% vs. 13.3%; P<0.001; test for interaction for pooled comparisons of old vs. new algorithm, P=0.006). Because of the findings in the 1055 infants on the new algorithm, both trials closed recruitment. However, targeting neonatal SpO2 is imprecise and these data allow no inferences about risks and benefits of other targets. Until longer-term data on survival and morbidity are available, the authors conclude it is prudent not to target an SpO2 of 85-89%. Final recommendations await information on the primary outcomes of disability-free survival, anticipated in 2014.

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