question: A patient was admitted to the hospital with chronic obstructive pulmonary disease.  His PO2 was 55 and PCO2 was 65.  A new resident orders 54% oxygen via the venturi mask.  One hour later, after the oxygen was placed, the nurse finds the patient with no respiration or pulse.  She calls for a Code Blue and begins cardiopulmonary resuscitation (CPR).  Explain why the patient stopped breathing.