Extended caffeine treatment reduced the mean time at less than 90 % Sao2 by 47 % ( 95 % CI , -65 % to -20 % ) to 50.9 ( 48.1 ) s/h at 35 weeks and by 45 % ( 95 % CI , -74 % to -17 % ) to 49.5 ( 52.1 ) s/h at 36 weeks .