Medical services outsourcing giant Envision Healthcare was created in late 2016 from the merger of ambulatory surgery center operator AmSurg Corp. and emergency room staffing firm and private ambulance service provider Envision Healthcare Holdings. The combined company's operating subsidiaries are American Medical Response (medical transportation services firm with more than 28,000 paramedics and EMTs), EmCare (the nation's largest emergency room staffing and management provider), and Evolution Health (customized mobile health care services). In all, Envision provides physician staffing services at some 780 hospitals in 45 states and owns and operates 260 surgery centers in 35 states and Washington, DC.