Re: Dealing with Device/Design changes by a "Letter to File" vs. 60601 Retesting
A critical components are all the components that can impair the safety of the appliance if replaced by components that are similar but not the same as far as the electrical and mechanical features are concerned. such as components assuring insulation between pri circuit and sec circuit (transformer, optical isolatior, X, Y capacitor), patient circuit and live part/enclosure (optical isolator, non-optical isolator) etc.
Of cource, if one component's specificaton can affect compliance with standard, this component should be treated as critical components. for eg. components affecting residual voltage (bleeding resistor), defibrillation protection (GDT), temperature test (sink design, opening) and so on.