[1] Ulster Hosp, UNDAH Trust, Dept Anaesthet, Belfast BT16 0RH, Antrim, North Ireland
[2] Ulster Hosp, UNDAH Trust, Dept Oral Surg, Belfast BT16 0RH, Antrim, North Ireland
[3] Queens Univ Belfast, Dept Anaesthet, Belfast BT9 7BL, Antrim, North Ireland