Quantitative evaluation of clinical course in surgical ICU patients: the data conform to catastrophe theory.

A response surface for critically ill patients is described. The coordinates of the three-dimensional response surface are two control variables, or state variables, related to aerobic and anaerobic metabolism, and a response variable, the A-VO2 difference. The data conform to a cusp catastrophe manifold. Cardiac insufficiency, adaptive response to stress, and sepsis may be distinguished by this model. The distinction between control and response variables is discussed.