Mean ( SD ) PaO2 8.7 ( 1.7 ) versus 7.9 ( 1.7 ) kPa ( p = 0.19 ) , PaCO2 6.7 ( 0.5 ) versus 7.3 ( 1.1 ) kPa ( p = 0.1 ) , mSpO2 89.7 ( 4.2 ) versus 89.8 ( 3.9 ) % ( p = 0.95 ) , compliance 5.0 ( 3.1 ) versus 4.7 ( 3.2 ) hours ( p = 0.8 ) in va-NIV versus pp-NIV respectively .