Note: Data were obtained from references 23–26
Advanced age is currently a more explicit risk factor for POCD, and similar results were obtained in the present study. Several studies suggest that the pathogenesis of POCD is neuroinflammation and age are related . The mechanism may be that brain volume and brain white matter integrity decrease with age. Moreover, blood flow to the brain decreases with age, resulting in reduced oxygen delivery, slow metabolism, and age-induced central nervous system apoptosis, which affects neurons, synapses, and neurotransmitters, leading to an increased incidence of POCD in older patients. At the same time, older patients often exhibit a variety of comorbid conditions, and the ability of the body to cope with the injuries caused by surgery and anaesthesia is consequently reduced. Therefore, the risk of perioperative complications and POCD also increases accordingly [31,32]. In conclusion, older patients are more likely to develop POCD after surgery.
The level of education is closely related to the occurrence of POCD . Feinkoh et al.  found that in middle-aged and older patients undergoing surgery, years of education are inversely proportional to the incidence of cognitive impairment, and patients with high cognitive reserve display more active brain activity and can better adjust or activate synaptic connections between neurones using neuronal reserve, bypassing damaged areas, and increasing synaptic efficacy to deal with injury. In addition, with low education, there may be exposure to more harmful factors in the living environment, and an unhealthier lifestyle. As such, there may be more serious pathological manifestations in the brain than that of their peers, such as Aβ deposition, which are exacerbated by anaesthesia and progress to cognitive deficiency .
In recent years, more researchers have focused on the association between dyssomnia and POCD. The results obtained in this study showed that sleep disturbance is an independent risk factor for POCD. Sleep accounts for about 1/3 of an individual’s life-span and is closely related to human health. Various aspects of sleep are affected to varying degrees in most older adults . Dyssomnia is not conducive to protein synthesis and the establishment of new synaptic connections in the brain, affecting the change in cerebral cortical cognitive potential, leading to neuroendocrine disorders, decreased immune function, deterioration of behaviour, anxiety, depression, irritability, and other complications, thereby inducing or aggravating postoperative cognitive dysfunction . A meta-analysis revealed that various types of sleep disorders, such as difficulty remaining asleep, reduced sleep duration, reduced sleep efficiency, and daytime dysfunction can significantly increase the risk of cognitive impairment . Studies have demonstrated that the intraoperative use of dexmedetomidine can significantly stabilise patient haemodynamics, reduce the occurrence of inflammatory reactions, inhibit free radical generation, reduce sleep disorders caused by the use of other anaesthetic drugs, and exert a certain protective effect on the sleep of patients under general anaesthesia .
Hypertension is a common cardiovascular complication in older patients, and studies suggest that hypertension is often accompanied by cerebrovascular and carotid atherosclerotic plaque, which leads to cerebrovascular autoregulation function. Under the stimulation of various related factors during the perioperative period, there can be local or whole cerebral blood flow, cerebral oxygen content further declines, central nervous system transmitter release is reduced, particularly the cholinergic nervous system function is declined, leading to impaired brain function, making hypertensive patients more prone to postoperative cognitive function damage . Spence et al. demonstrated that for every 10 mmHg increase in systolic blood pressure, the risk of cognitive dysfunction increased by 7% compared with that of the control group, and the systolic blood pressure was > 160 mmHg, and cognitive decline was significantly increased .
The duration of anaesthesia was also an independent risk factor for the onset of POCD in this group, and the mean anaesthesia time of patients in the POCD group was higher than that in the non-POCD group, and perhaps the more complex surgical steps during this period led to the occurrence of POCD.More complex surgical steps imply an increase in surgical anaesthesia duration,one study revealed a significant increase in POCD in patients who underwent surgery exceeding 450 min, and prolonged surgical time is a further important predictor of POCD . A systematic review by Freddi Segal-Gidan et al.  concluded that shorter anaesthesia time was associated with less risk of POCD. Animal studies confirmed that anaesthesia exposure can change amyloid and tau in mice, which leads to cognitive dysfunction .
Currently, the relationship between intraoperative blood pressure and postoperative cognitive function is controversial. Intraoperative hypotension in this study was an independent risk factor for POCD. Operative hypotension leads to a low perfusion state of the brain blood supply and induces free radical damage and other pathological changes. In addition, oxidative stress response can also cause a range of changes in neuronal degeneration and protein apoptotic genes, reducing the molecular expression that create and maintain synaptic connections, thereby impacting memory and cognitive function. A prospective clinical study demonstrated that a single longest cerebrovascular modulation of BP change over 5.03 min was associated with decreased postoperative cognitive function . Therefore, sustained hypotension during general anaesthesia may cause damage to the nervous system of patients with chronic insufficient cerebral perfusion (such as older patients), and preventing intraoperative hypotension helps to prevent POCD .
Due to the peculiarity of oral tumour surgery, patients were unable to test for language after surgery, and to mitigate the impact on neuropsychological testing, patients failed to study their altered cognitive function within 7 d after surgery, and in the multivariate analysis, some insensitive indicators were not analysed. In this study, diabetes mellitus, coronary heart disease, history of cerebral infarction, and hypokalaemia were associated with the onset of POCD, but were not independent risk factors for the onset of POCD.A small number of studies have found that risk factors affecting postoperative cognitive impairment may also include intraoperative bleeding, prolonged ICU stay, secondary surgery, and postoperative infection. These two conditions may be related to the present study, this study as a single-centre experiment with a small sample size, so the results no statistically significant differences. Consequently, multicentre observational studies involving large cohorts are required to determine whether current risk factors are of high predictive value.