Abstract: Objective To investigate the application value of near-infrared spectrometer (NRIS) in monitoring cerebral oxygen saturation during radical operation of senile colorectal cancer (CRC). 
Methods In total, 120 elderly patients with rectal cancer who underwent elective radical surgery for CRC in our hospital were prospectively included as the research subjects. They were randomly divided into a conventional ventilation group (control group, n=60) and a NRIS monitoring technology combined with mechanical ventilation group (research group, n=60) using a random number table method. The arterial blood gas analysis results, as well as the changes in arterial blood carbon dioxide (CO2) partial pressure (PaCO2) and arterial oxygen saturation (SaO2), before surgery (T0), at 5 min before pneumoperitoneum (T1), 20 min after pneumoperitoneum (T2), 1 h after pneumoperitoneum (T3), 2 h after pneumoperitoneum (T4), and 20 min after pneumoperitoneum (T5) were compared between two groups, and cognitive function of the patients at 1 d before surgery, and at 1 d after surgery (M1), 4 d after surgery (M2), and 7 d after surgery (M3) was evaluated using the Montreal Cognitive Assessment Scale (MoCA). Enzyme-linked immunosorbent assay (ELISA) was used to detect serum cortisol and central nervous system specific protein (S-100β), and the intraoperative changes in rSO2 and postoperative neurological complications in each group were recorded. 
Results There was no statistically significant difference in interactions between groups, time points, and time points between groups in terms of Hb and Lac levels (P＞0.05). There was no statistically significant difference in interactions between groups and time points in terms of PaCO2, rSO2, and pH (P＞0.05). There was no statistically significant difference in interactions between groups and time points in terms of  PaCO2 and pH (P＞0.05). There was a statistically significant difference in interactions between groups and time points in terms of rSO2 (P＜0.05). The MoCA scores of both groups decreased first and then increased with time, and there was a significant difference in the interaction between time points, and time points between groups  (P＜0.05), while there was no significant difference between groups (P＞0.05). Both groups did not experience severe cerebral hypoxia during surgery. The incidence of mild and moderate cerebral hypoxia during surgery, as well as the incidence of postoperative delirium and POCD in the research group, were lower than those in the control group, and the difference was statistically significant (P＜0.05). Before surgery, no significant difference was found in serum cortisol and S-100β in the two groups (P＞0.05). After surgery, the levels of serum cortisol and S-100β were higher than those before surgery, and S-100β level was higher in the research group than in the control group, showing a significant difference (P＜0.05). There was no statistically significant difference in cortisol levels between two groups (P＞0.05).  
Conclusion The use of NRIS monitoring technology combined with mechanical ventilation can significantly increase rSO2 in elderly colorectal patients undergoing radical resection for CRC, and effectively reduce the risks of cerebral hypoxia during the operation and postoperative neurological complications, which is conducive to reducing the early cognitive dysfunction after operation. 

Key words: colorectal neoplasms, near-infrared spectrometer, mechanical ventilation