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.