How can intrabdominal hypertension be graded?

IAH is defined by the World Society of Abdominal Compartment Syndrome as:

A sustained or repeated pathological elevation in IAP >12 mmHg

It is graded according according to pressure:

Grade I
12-15 mmHg 0.5
Grade II
16-20 mmHg 0.5
Grade III
21-25 mmHg 0.5
Grade IV
>25 mmHg 0.5