Completely taking over a physiological function by extracorporeal means is known as what?

The concept of completely taking over a physiological function by extracorporeal means is best described as "Performance." This term in the context of ICD-10-PCS coding refers to an intervention that fully assumes the body’s usual function using external devices or machines. A clear example of this is dialysis, where a machine performs the kidney's job of filtering blood when the kidneys are unable to do so.

In terms of other options, "Assistance" implies support or help rather than a taking over of function. "Substitution" generally refers to replacing a part of a physiological process but does not capture the complete takeover aspect. "Restoration" suggests bringing something back to its original state or function, which again does not convey the idea of an external source fully performing the function. Thus, "Performance" accurately reflects the complete assumption of a physiological function by extrinsic means.