Complex sentence: The disadvantages are that there is a practical time limit on its use (1-2 hours) because the tourniquet is restricting blood flow to the extremity, and the tissues of the extremity are not getting oxygen.
Split into simpler sentences: The disadvantages are that there is a practical time limit on its use (1-2 hours) due to the tourniquet restricting blood flow to the extremity. Thus, the tissues of the extremity are not getting oxygen.