Figure 3.

Illustration of how CERAD-NP total scores (z-score) change from the preoperative to the postoperative period (V0 vs. V3) depending on the delirium status during the postoperative period (top = nondelirious; bottom = delirious), age (x-axis) and functional improvement/deterioration after surgery as assessed by the Barthel Index (y-axis). Color coding indicates either postoperative cognitive dysfunction (POCD; toward red) or cognitive improvement (POCI; toward green), while yellow indicates no change. The model based on this study’s data reveals that no patient, irrespective of age, would be affected by POCD (defined as a z-score change of ≤−1)⁴ if neither POD nor deterioration of functional abilities were present. In contrast, almost any age group would develop POCD if they were affected by POD, unless they functionally improved by about 10 (70 years of age or below) to 30 (90 years of age or above) points on the Barthel scale after surgery. The notion of POCI in patients improving by ≥1 z-score is difficult to interpret and may be either subject to enhanced cognitive abilities due to improved physical abilities or retest training effects (see Discussion for a more elaborate discussion).