What can cause a low oxygen level in an 83 year old female?

See below. This could be potentially serious. You should discuss these with your physician. He/she will thoroughly evaluate you and let you know what's going on.
Usually, low oxygen . I would take the patient to be evaluated if he is not already doing so. In addition, proper measurements and examinations such as a chest x-ray arterial blood gas and careful physical examination will often lead to the appropriate answer. In an 83-year-old, congestive heart failure pneumonia COPD or even blood clots in the lung (pulmonary emboli) are leading candidates as the cause of this problem.