Patient positioning apparatus and mattress

A patient positioning apparatus for use with a mattress has a first lateral tilt bladder and a third lateral tilt bladder underlying a first side of the mattress, and a second lateral tilt bladder and a fourth lateral tilt bladder underlying a second side of the mattress. The tilt bladders are inflatable to alter the position of a patient lying on the mattress, and inflation and/or deflation of the lateral tilt bladders is controllable by a controller. A first check valve allows fluid communication in one direction from the third lateral tilt bladder to the first lateral tilt bladder, and a second check valve allows fluid communication in one direction from the fourth lateral tilt bladder to the second lateral tilt bladder.