Background: Life depends on oxygen, especially for patients having cardio thoracic surgery; absent constant oxygen therapy, cardiac surgery cannot be performed successfully at any stage of the healing process. Aim: The study aimed to explore the effect of protocol of care regarding oxygen therapy for patients after cardiac and thoracic surgery on nurse's performance and health outcome. Subjects and method: Research design: There was a quasi-experimental study design. Setting: The investigation was conducted at the critical care units of three hospitals in Port-Said, Egypt—Al-Shifa Medical Complex, Alsalam Hospital, and Alzohor Hospital—all of which are part of the Egypt Health Care Authority. Sample: 50 nurses who worked in postoperative cardiac and thoracic surgery units and intensive care units, as well as 50 patients who had been transferred to the aforementioned settings at the time of data collection, were accounted for in the purposeful sampling.