With advances in medicine and technology, the world's population is aging, a trend that is especially noticeable among the Chinese people, with an estimated 366 million older Chinese adults expected by 2050 (https://population.un.org/wpp/DataQuery). Elderly individuals often suffer from cognitive impairment, a disease characterized by declining memory and trouble learning new things, with the likelihood of progressing to dementia in the future (1). It has been reported that the prevalence of cognitive impairment ranges from 9.7% to 23.30% in Chinese people, with a figure of 20.8% for people aged 65 years and older (2). Numerous studies have reported that being an older adult with cognitive impairment is associated with a series of poor clinical outcomes, such as falls (3), lower quality of life (4), and increased mortality (5), resulting in a substantial healthcare burden for families and society alike. In mainland China, it is estimated that the annual healthcare cost for patients with Alzheimer's disease is $167.74 billion US, far more than the estimate reported by the World Alzheimer Report of $28.18 billion US (6).

Several studies have reported that community-dwelling older adults with cognitive impairment have an increased risk of mortality compared to those with normal cognition (7–10). A large cohort study recently reported that community-dwelling older adults with cognitive impairment are at increased risk of mortality compared to those with normal cognitive function (11). The possible reasons for the association between cognitive impairment and mortality were etiologic conditions such as multiple comorbidities (12) or inability to efficiently process information, resulting in noncompliance with medical care and unlikely maintenance of a healthier lifestyle (13). Moreover, the impact of cognitive impairment on adverse clinical outcomes among hospitalized older adults has become increasingly studied (14, 15). Indeed, inpatients suffering from cognitive impairment may have worse clinical outcomes than community-dwelling older adults due to forgetting to take medication or failing to follow clinicians' advice. In addition, poor functional capacity and multiple comorbidities make older inpatients more vulnerable to the detrimental effect of cognitive impairment than older people living in the community. Therefore, identifying the association between cognitive impairment and mortality among hospitalized older people is very important.

Several studies from Western countries have explored the impact of cognitive impairment on mortality among older adults in hospital settings (16–19). One study involving 539 emergency department inpatients reported that patients with cognitive impairment had an approximately 3.10-fold higher risk of mortality than those with normal cognitive function, indicating that emergency medical personnel need to pay much more attention to older inpatients (19). Similar results were also found in another study (18). However, these abovementioned studies focused on western countries. To date, one study has explored the association between cognitive or physical frailty and the composite outcome of readmission and death among Chinese elderly inpatients with cardiovascular disease, reporting that elderly inpatients with cognitive impairment were not associated with worse outcomes compared to robust patients (20). However, this study was from a single center with negative results. Therefore, a prospective multicenter study with a large-scale cohort sample exploring the association with mortality among older Chinese inpatients is needed. Our aim was to use a national prospective cohort study to estimate the prevalence of cognitive impairment in older inpatients and identify whether there was an independent association between cognitive impairment and 30-day mortality among older inpatients in China after adjusting for age, sex, education frailty, depression, and activities of daily living (ADL). Moreover, our study also examined the association between cognitive impairment and mortality with different subgroup analyses, such as sex, age group, depression, and frailty. We hypothesized that there is an independent association between cognitive impairment and 30-day mortality in older Chinese inpatients.

To the best of our knowledge, this is the first study to explore the association between cognitive impairment and 30-day mortality among older Chinese inpatients with a large multicenter sample. Our study found that inpatients with cognitive impairment have an independent 1.76-fold increased risk of 30-day mortality compared to those without cognitive impairment after adjusting for demographics and geriatric syndrome variables. This indicates that early screening for cognitive function and participation in a corresponding intervention program by older hospitalized Chinese patients is urgently required to improve poor clinical outcomes.

In our large-scale cohort study, the prevalence of cognitive impairment was 20.5%, as assessed by the Mini-Cog assessment instrument. This result is higher than the 6.54% in an urban population and 7.43% in a rural population reported by a previous study using the MMSE score (31), but it is similar to other results (27%) (18). On the other hand, another study reported that the prevalence of cognitive impairment among older adults in an emergency surgical setting was 61.0% using Montreal Cognitive Assessment, with a cutoff score of ≤ 23 (19). The main reasons for these differences are subject age, disease type and condition, and different cognitive assessment tools. In general, hospitalized patients and older adults have a higher prevalence of cognitive impairments than community-dwelling older adults because comorbidity and greater disease severity are risks of cognitive impairment (32). However, screening and diagnosis for cognitive function in Chinese inpatients are limited. According to the results of a recent study (2), most patients with cognitive impairment are not diagnosed because of a lack of dementia specialists. This results in a large healthcare issue for those groups and prevents meeting the needs of people with dementia.

Several factors are known to determine the association between cognitive impairment and 30-day mortality. First, inpatients with cognitive impairment are at increased risk of mortality through etiologic conditions, indicating that patients with cognitive impairment suffer more from multiple diseases such as stroke, chronic obstructive pulmonary disease, and other multisystem disorders than patients with normal cognition (12). Second, cognitive impairment damages the capacity to obtain, understand, and even process medical services. This leads to poor health behaviors and an unhealthy lifestyle (33), including being unable to recognize the signs of disease, failing to follow prescribed medication regimes, and difficultly participating in regular exercise (13). Third, sarcopenia and frailty, two well-known geriatric syndromes, were reported as risk factors for cognitive impairment, as confirmed in a systematic review and meta-analysis (34, 35). Therefore, cognitive impairment, to a certain extent, reflects these two geriatric syndromes, which are associated with mortality. Although stratified analysis has shown that the association between cognitive impairment and 30-day mortality is higher in females (OR = 3.63; 95% CI: 1.93–6.79) than in males (OR = 2.36; 95% CI: 1.36–4.09), the interaction was not significant. Examining the sex-specific differences in the impacts of cognitive impairment on mortality, we were unable to draw conclusions based on previous studies. On the one hand, a previous study (36) described that the risk of mortality was higher in males than in females, possibly due to males' greater likelihood of smoking and drinking, whereas others (37) reported that females demonstrate a higher risk of mortality. We believe the main reasons might be due to different ethnicities, regions, sample sizes, and education levels (11). Therefore, more evidence is required to explore this important issue.

Our study found that inpatients with cognitive impairment have an increased risk of 30-day mortality than inpatients with normal cognitive function. This association still existed after performing a stratified analysis, consistent with previous studies reporting this association in different types of older patients (7, 9, 38–41). In recent years, the impact of cognitive impairment on mortality in Chinese community-dwelling older adults (11, 36) has been well studied; however, few studies have been conducted on hospitalized patients (18). The prevalence of mortality in inpatients was higher than that in community-dwelling older adults, and the adverse impact of cognitive impairment on clinical outcomes was also severe in hospitals, with low levels of recognition by medical personnel. Our study implies that early screening and diagnosis for cognitive impairment is very significant. Once patients are screened for cognitive impairment in hospital wards, corresponding interventions need to be carried out. For example, clinicians can write a comprehensive prescription, such as psychosocial interventions (42), cognitive therapy (cognitive stimulation therapy, cognitive rehabilitation, cognitive training) (43), and medications for patients. Medical health education interventions also need to be implemented for both patients and their family members. Thus, the more often and earlier the cognitive impairment screening is performed, the better the clinical outcome will be.

There are several strengths and limitations in our study. First, our study included a large-scale sample size and was a multicenter study that explored the association between cognitive impairment and 30-day mortality in older Chinese inpatients. Second, we used different adjusted models and sensitivity analyses, suggesting that our results are robust. However, some limitations need to be considered. First, the follow-up in our larger-scale cohort study is relatively short compared with other published studies (one-year mortality or more), which fails to generalize the association of long-term cognitive impairment with mortality. Second, the Mini-Cog cognitive function assessment tool is a screening tool and cannot truly diagnose, which may underestimate or overestimate the prevalence of cognitive impairment and further influence the impact of cognitive impairment on 30-day mortality. Third, although we adjusted for some factors related to 30-day mortality, such as depression, ADL, and frailty, we did not control for other factors, comorbidities, or potential confounding factors, possibly influencing the reported results. To address this issue, we are currently continuing the multiple-center follow-up study for a 1-year period. Furthermore, future prospective cohort studies exploring the association between cognitive impairment and mortality, adjusting for more potential confounding factors, among older Chinese inpatients with a long-term follow-up period should be implemented, and a larger samples of randomized controlled trials should be implemented to identify whether effective interventions for cognitive impairment could help to reduce the rate of short-term or long-term mortality.

In this large multicenter longitudinal study, cognitive impairment was prevalent in older Chinese hospitalized patients and was significantly associated with an increased risk of 30-day mortality. These observations are relevant to clinicians and nurses because they can potentially identify high-risk older inpatients for poor clinical outcomes. As a result, corresponding adjustment interventions, including early geriatric involvement and cognitive therapy, combined with a family program, can be preemptively performed. We suggest that clinical medical personnel routinely perform early cognitive function screening with bedside tools on admission to carry out a comprehensive therapeutic regimen for older inpatients.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by the Ethics Committee of Peking Union Medical College Hospital (S-K540). The patients/participants provided their written informed consent to participate in this study.

XWu responsible for the concept and design. TX analyzed and interpreted the data. X-MZ and JJia participated in designing the study and drafted the initial manuscript. NG, CZ, ZL, DL, HW, JJin, XWen, and SZ carried out the data acquisition and patient interviews. All authors contributed to the article and approved the submitted version.

This work was supported by the Special Research Fund for Central Universities, Research Centre of Nursing Theory and Practice, Peking Union Medical College [Grant Number 2018PT33001] and CAMS Innovation Fund for Medical Sciences [Grant Number 2018-I2M-AI-009].

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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