The ASA score was evaluated as both a 5-level ordinal variable, with values of 1,2,3,4, and 5, and as a dichotomous variable (ASA [is greater than or equal to] 3 and ASA [is less than] 3, corresponding to the NNIS scoring system).
An NNIS risk index score was calculated for each patient by assigning one point each for a contaminated wound, an ASA score [is greater than or equal to] 3, and surgical procedures lasting longer than the NNIS-derived 75th percentile for the duration of the procedure (23).
Two variant scores were also computed; in one of these, a chronic disease score [is greater than or equal to] 5,000 was substituted for ASA score [is greater than or equal to] 3, and in the other, a point was added to the NNIS score for a chronic disease score [is greater than or equal to] 5,000.
In this population, the NNIS risk index was correlated with infection status (Figure 2A).
The chronic disease score performed comparably with the ASA score as a component of the NNIS risk index, and an NNIS-like index based on both the chronic disease and ASA scores performed better than the conventional NNIS index.