Apatient was admitted to the hospital with chronic obstructive pulmonary disease. his po2 was 55 and pco2 was 05. 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.