AC failure was significantly worse with SPU dressings ( 10/47 [ 21 % ] ) than with BPU + SPU dressings ( 2 / 43 [ 5 % ] ; P = 0.03 ) , but not significantly different to TA + SPU ( 6/56 [ 11 % ] ; P = 0.18 ) or SSD + SPU ( 8/49 [ 16 % ] ; P = 0.61 ) .