In hospitalized critically ill patients (P), how does turning and repositioning every two to four hours (I), compared to the use of pressure redistributing support surfaces (C) prevent the occurrence of pressure ulcers (O),during three months hospitalization (T)?

In hospitalized critically ill patients (P), how does turning and repositioning every two to four hours (I), compared to the use of pressure redistributing support surfaces (C) prevent the occurrence of pressure ulcers (O),during three months hospitalization (T)?