In this model, which is unique, the role of the medical director is substantially different. Scope of practice and all treatment protocols are developed by the Dutch Ambulance Institute on a national basis, and cannot be unilaterally changed at the local level by individual physicians. Scope and protocols are reviewed, revised, and announced every four years, and any physician who wishes a change to those protocols must provide sound reasons and present a successful argument before a committee of the DIA. The medical managers for each private carrier operate in a role approximating that of medical director, but only for that one company; their authority does not extend to other companies operating in the same community. These individuals do perform quality service functions such as chart audits and complaint investigation, but they cannot unilaterally change treatment protocols. They may provide guidance, advice and direction to paramedics by telephone or radio, or they may attend the scene in person to provide care. The Dutch system also operates a network of four helicopters staffed by physicians for rapid response to support paramedics in the field. While many of the individuals working in the Dutch system may be occasionally described as 'emergency physicians', the majority, as in the Franco-German model, are actually anesthetists.