BACKGROUND: More than 600,000 adults in the United States experience a cardiac arrest each year. After resuscitation from cardiac arrest, most patients receive mechanical ventilation. The oxygenation target that optimizes neurologic outcomes after cardiac arrest is uncertain. RESEARCH QUESTION: After cardiac arrest, does a lower oxygen saturation (SpO STUDY DESIGN AND METHODS: We conducted a secondary analysis of patients who experienced a cardiac arrest before enrollment in the Pragmatic Investigation of optimal Oxygen Targets (PILOT) trial. The PILOT trial assigned critically ill adults receiving mechanical ventilation to a lower (88-92%), intermediate, (92-96%), or higher (96-100%) SpO RESULTS: Of 2,987 patients in the PILOT trial, 339 (11.3%) experienced a cardiac arrest before enrollment: 221 were assigned to a lower-or-intermediate SpO INTERPRETATION: Among patients receiving mechanical ventilation after a cardiac arrest, use of a lower-or-intermediate SpO