Fuzzy logic
The IPI algorithm was developed based on the data from a group of medical experts (anesthesiologists, nurses, respiratory therapists, and physiologists) who evaluated cases with varying parameter values and whom assigned an IPI value to a predefined patient status. A mathematical model was built using patient normal ranges for these parameters and the ratings given to various combinations of the parameters by these professionals. Fuzzy logic, a mathematical method which mimics human logical thinking, was used to develop the IPI model.