Preoperative cerebrospinal fluid β-Amyloid/Tau ratio and postoperative delirium

Objective: The neuropathogenesis of postoperative delirium remains unknown. Low cerebrospinal fluid (CSF) beta-amyloid protein (A beta) and high CSF Tau levels are associated with Alzheimer's disease. We, therefore, assessed whether lower preoperative CSF A beta/Tau ratio was associated with higher incidence and greater severity of postoperative delirium. Methods: One hundred and fifty-three participants (71 +/- 5 years, 53% men) who had total hip/knee replacement under spinal anesthesia were enrolled. CSF was obtained during initiation of spinal anesthesia. The incidence and severity of postoperative delirium were determined by Confusion Assessment Method (CAM) and Memorial Delirium Assessment Scale (MDAS) on postoperative day 1 and 2. A beta 40, A beta 42, and Tau levels in the CSF were measured by enzyme-linked immunosorbent assay. The relationships among these variables were determined, adjusting for age and gender. Results: Participants in the lowest quartile of preoperative CSF A beta 40/Tau and A beta 42/Tau ratio had higher incidence (32% vs. 17%, P = 0.0482) and greater symptom severity of postoperative delirium (A beta 40/Tau ratio: 4 vs. 3, P = 0.034; A beta 42/Tau ratio: 4 vs. 3, P = 0.062, the median of the highest MDAS score) as compared to the combination of the rest of the quartiles. The preoperative CSF A beta 40/Tau or A beta 42/Tau ratio was inversely associated with MDAS score (A beta 40/Tau ratio: -.12 +/- 0.05, P = 0.014, adj. -0.12 +/- 0.05, P = 0.018; Ab42/Tau ratio: -0.65 +/- 0.26, P = 0.013, adj. -0.62 +/- 0.27, P = 0.022). Interpretation: Lower CSF A beta/Tau ratio could be associated with postoperative delirium, pending confirmation of our preliminary results in further studies. These findings suggest potential roles of A beta and/or Tau in postoperative delirium neuropathogenesis.