What are the causes of postoperative hypoxia?

Postoperative hypoxia is considered a postoperative pulmonary complication. This can be caused by lack of alveolar ventilation, lack of alveolar perfusion, or decreased alveolar diffusion. (Alveolar: Pertaining to the alveoli, the tiny air sacs in the lungs where the exchange of gasses occurs) So, yes, withing 48 hours or so, this can develop.