## 3 Results  
All enrolled patients were sent to the general ward after surgery; no serious postoperative complications except for delirium were observed. Postoperative delirium developed in 6 of 37 patients (16.2%): 4 females (67%) and 2 males (33%). The mean age of these patients was 72.7 \(\pm\) 3.0 years. Affected patients presented symptoms of hyperactive delirium, including rambling, restlessness, hallucinations, and aggressiveness. The demographics and surgical characteristics of the delirium and non-delirium groups are shown in Table 1. The Mental component Summary (MCS) of the 36-Item Short-Form Health Survey (SF-36) was marginally lower in the delirium group than in the non-delirium group (\(p\) = 0.061). There were no significant differences in age, gender, American Society of Anesthesiologists class, history of dementia, physical component summary of the SF-36, surgical site, surgical duration, volume of intraoperative blood loss, or total units of transfused packed red blood cells. According to the results of the LMM, the interactions between group and time were significant in the theta waves (\(p\) = 0.083), H-beta waves (\(p\) = 0.014), gamma waves (\(p\) = 0.023), and tension index (\(p\) = 0.105), while the other variables were not significant. The results of performing a group post hoc analysis of these variables are shown in Table 2. In patients with delirium, H-beta and gamma waves and the tension index increased, while theta waves decreased, within 1 week after surgery. Patients in the delirium group showed significantly more changes in H-beta (19.3%; \(p\) = 0.003), gamma (18.8%; \(p\) = 0.006), and theta waves (\(-\)23.2%; \(p\) = 0.016), as well as the tension index (7.8%; \(p\) = 0.011), within 1 week after surgery from baseline compared to patients in the non-delirium group. In the graph of H-beta, gamma, and theta waves and tension index, patterns of peaks and troughs 1 week after surgery followed by recovery to baseline levels by 3 months after surgery were noted in the delirium group, whereas a somewhat flat pattern was noted in the non-delirium group (Figure 3). \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Delirium (_n = 6_) & **Non-Delirium (_n = 31_)** & _p-Value_ \\ \hline Age (years) & 72.7 \(\pm\) 3.0 (71–78) & 70.1 \(\pm\) 6.4 (60–84) & 0.353 \\ \hline Gender & & & \\ Female & 4 (67) & 17 (55) & 0.680 \\ Male & 2 (33) & 14 (45) & \\ \hline ASA class & & & \\ I & 0 & 1 (3) & \\ II & 3 (50) & 13 (42) & \textgreater{}0.999 \\ III & 3 (50) & 17 (55) & \\ \hline History of dementia & 1 (17) & 1 (3) & 0.302 \\ \hline SF-36 & & & \\ PCS & 27 \(\pm\) 12 & 33 \(\pm\) 14 & 0.313 \\ MCS & 40 \(\pm\) 19 & 53 \(\pm\) 16 & 0.061 \\ \hline Surgical site & & & \\ Cervical & 1 (17) & 6 (19) & \textgreater{}0.999 \\ Thoracolumbar & 5 (83) & 25 (81) & \\ \hline Surgical duration (min) & 198 \(\pm\) 52 & 201 \(\pm\) 56 & 0.934 \\ \hline Intraoperative blood loss (mL) & 317 \(\pm\) 177 & 465 \(\pm\) 258 & 0.178 \\ \hline Total units of transfused & & & \\ packed RBCs & 0.3 \(\pm\) 0.7 & 1.0 \(\pm\) 1.6 & 0.308 \\ \hline \end{tabular} Values are reported as the mean \(\pm\) standard deviation (range) or number (%). ASA: American Society of Anesthesiologists class; SF-36: 36-Item Short-Form Health Survey; PCS: Physical Component Summary; MCS: Mental Component Summary; RBCs: red blood cells.  
\end{table} 
Table 2: Percentage changes in EEG signals from baseline to within 1 week and to 3 months after surgery in the delirium and non-delirium groups.