Parker Tracheotomy Fig F.G 1 16 Y17.160.16 2 18 Y17.160.18 3 20 Y17.160.20 4 22 Y17.160.22 5 24 Y17.160.24 6 26 Y17.160.26 7 28 Y17.160.28 8 30 Y17.160.30 9 32 Y17.160.32