Compared with some research hotspots such as deep vein thrombosis, pulmonary embolism, and cardiovascular and cerebrovascular diseases of the lower extremities, POD is a common phenomenon, but it is easily ignored by orthopedic surgeons in elderly patients with hip fractures. Probably because POD is often an acute transient abnormality, resulting in missed diagnosis and misdiagnosis, which may lead to patients not receiving timely, reasonable, and effective intervention6, 11-13. In this study, we found that POD may be associated with a series of early adverse prognoses. Compared with the non-delirium group, the delirium group was more likely to have perioperative complications and the incidence of pulmonary infection, hypoalbuminemia, electrolyte disturbance, indigestion, bedsores, and anemia was higher. In addition, the length of stay was longer in the delirium group. Moreover, the mortality rate was 27.3% in the delirium group within one year after operation, which was five times that of the non-delirium group.
Our results are similar to those of previous studies. Hamilton et al.9 reviewed 34 of 4968 screened citations and found that delirium was associated with a four-fold increase in the risk of death. Mosk et al.7 reported that delirium was correlated with a longer hospital stay, increased associated with complications, institutionalization, and 6-month mortality by observing 566 patients with hip fractures who were over the age of 70. Bellelli et al.14 reported that hypoactivity and mixed POD were associated with increased 6-month mortality risk. They observed 571 patients in which the morbidity of delirium was 38.5%, whereas the mortality rates of non-delirium and delirium groups separately were 8.3% and 24.1%, respectively. Bai et al.4 enrolled a total of 6288 patients and reported the prevalence of POD was 28% (23%–34%). They found that approximately one-fourth of patients undergoing hip fracture surgery went on to develop POD, and delirium increased both short-term and long-term mortality in these patients. Recently, Bielza et al.5 observed 383 patients with hip fracture who were over 70 years of age and found that 212 patients had POD; they found no correlation between delirium and mortality, walking ability, length of stay, or clinical complications. However, the in-hospital mortality of non-delirium and delirium groups was 4.6% and 3.3%, which is obviously lower than previously reported mortality rates of geriatric hip fractures. This difference may be related to the relatively short duration of their observation period, as they only collected data during the hospital stay. Therefore, there is a positive correlation between delirium and complications, as well as mortality, in our study and several similar studies. According to our results, early detection, early diagnosis, and early treatment of POD are very important and have positive clinical significance for reducing perioperative complications and the length of hospital stays, and improving mortality.
POD is correlated with early postoperative poor prognosis. The underlying reason may be that POD is a manifestation of systemic inflammatory responses, not just local stress responses. In 2008, Van Munster et al. first proposed that the systemic inflammatory response plays an important role in the occurrence of delirium15. Subsequent research on the mechanism of clinical POD caused by systemic inflammatory response has shown that acute peripheral inflammatory stimuli (such as infection, surgery, or trauma) can induce activation of parenchymal cells to promote the expression of proinflammatory cytokines (such as tumor necrosis factor, interleukin 6, and interleukin 1β) and chemokines (such as monocyte chemotactic protein 1) in the central nervous system, which causes destruction of the blood-brain barrier and subsequent neuron and synaptic dysfunction, resulting in delirium16. According to the results of this study, blood platelet counts and C-reactive protein levels were higher in patients with POD; whereas, hemoglobin, blood calcium, albumin, prealbumin, and total cholesterol levels were lower. These results indicate that delirium is indeed related to systematic inflammation, coagulation changes, and nutritional status of the whole body, not just local manifestations of the nervous system. In addition, Lee et al.17 found that about 30.2% (70 cases) of older adult hip fracture patients had delirium after surgery, of which 20% (14 cases) continued to experience delirium 4 weeks after surgery, indicating that not all delirium is temporary. Indeed, it may sometimes appear to be continuous until the patient's whole-body condition is adjusted. Therefore, POD needs to be treated as soon as possible to be corrected in time. Previous studies reported that delirium results from the combined effects of environmental, pathological, and physiological factors6, 11, 12. Thus, early treatment should not just be symptomatic use of antipsychotic drugs such as haloperidol, olanzapine, and aripiprazole, but should also involve etiological treatments to reduce pain and suffering, correct hypoproteinemia and anemia, restore water and electrolyte balance, provide adequate oxygen inhalation and nutritional support, ensure good sleep, and allow patients to carry out early functional exercises.
In addition, early surgery may be an important measurement to prevent delirium and reduce mortality. The results of this study showed that the delirium group had a longer injury-to-surgery time than the non-delirium group. Pioli et al.18 considered the delay of surgery to be a risk factor for delirium. For older adult hip fracture patients with mild to moderate cognitive impairment, early surgery should be one of the preoperative goals. Other scholars have reported that early surgical treatment, epidural anesthesia, and a shortened hospital stay can reduce mortality following hospitalization of elderly patients with hip fractures3, 19, 20. Therefore, in view of the characteristics of hip fractures in the older adult, active development of geriatric wards, multidisciplinary cooperation, and shortening the waiting time for surgery will help reduce POD and improve the early prognosis of patients.
This study has three limitations. First, although the gold standard for diagnosis of delirium, the CAM assessment, was used in this study and determined by individuals qualified as associate chief physician or above, the core symptoms of delirium are difficult to define and clinical symptoms, severity, and progression, are difficult to identify. As such, the CAM diagnosis method is based on the subjective judgment of the clinician and not quantitative scores10, so there is a certain degree of subjective bias. Second, a valid malnutrition diagnostic measure (eg MNA / MNA-SF) was not conducted in this study. In addition, as the duration, classification, and severity of delirium were not observed in this study, a prospective multicenter cohort study will be used for further analysis.