In the PSV and T-piece groups , the average RSBI at 30-minute SBT was 67.18 11.55 breaths per min/L and 99.11 15.53 breaths per min/L , respectively ( P < 0.01 ) , and the average RSBI was 69 33 % and 119 35 % , respectively ( P < 0.01 ) .