Envision Healthcare Holdings, Inc., formerly CDRT Holding Corporation, is a holding company. The Company, through its subsidiary, provides physician-led medical services in the United States. It operates in two segments: EmCare Holdings, Inc. (EmCare) and American Medical Response, Inc. (AMR). Its EmCare segment is a provider of integrated facility-based and post-acute care physician services to healthcare facilities in the United States. Its AMR segment has developed a network of ambulance services and other healthcare transportation services in the United States. It provides Emergency Department (ED) physician services to hospitals and other facilities. Its hospitalist services include inpatient physician services. It provides anesthesiology services to hospitals, free-standing ambulatory surgery centers and physician offices. It provides radiology, including tele-radiology services to hospitals. It offers management, oversight and surgeon staffing for trauma surgery services.