Postoperative delirium is associated with an increased number of different complications, such as prolonged hospitalization, long-term cognitive impairment and increased mortality[14]. Fortunately, up to 40% of delirium can be prevented [1]. Therefore, strengthening the monitoring of delirium, supporting early prevention and identification will be an important part of the care of patients with cardiovascular surgery. Based on age, CPB duration, postoperative MV, postoperative Serum Sodium, this study constructed a risk prediction model for delirium in patients with cardiovascular surgery, and provided medical staff with an accurate and objective assessment tool. The Nomogram model is more specialized than the ICU patient delirium prediction model (PRE-DELIRIC) constructed by Dutch scholars Boogaard[15] and the early delirium risk prediction model (E-PRE-DELIRIC) constructed by Wassenaar[16]. It is more suitable for the Chinese population compared with the prediction model of delirium after coronary artery bypass grafting constructed by domestic scholars[17], it has a wider scope of application and can assess the risk of delirium in all patients with cardiovascular surgery. The independent risk factors in the prediction model of this study are easy to obtain, and the Nomogram model is characterized by its ability to single and intuitively express the results of a complex statistical model, and assign corresponding scores to the influencing factors of the end-point event. Points to calculate the probability of an end-point event. This allows medical staff to start the assessment at the beginning of the patient's postoperative CSICU treatment, and it is easier to use the iconic model for assessment, which is convenient for nursing staff to use.
This study found that age was an independent risk factor for the occurrence of delirium in patients after cardiovascular surgery. Numerous studies[2] have shown that advanced age is a high-risk factor for postoperative delirium. Elderly patients have degeneration of body function and brain tissue itself. They also have reduced levels of various central neurotransmitters such as acetylcholine and epinephrine. At the same time, due to obstructed brain function, patients often have cognitive dysfunction, which may be the cause of the high incidence of delirium[18, 19]. CPB duration was significantly related to the occurrence of postoperative delirium. The longer CPB duration, the higher the incidence of delirium. This finding is similar to that found in previous studies[20]. One of the hypotheses for the development of delirium is the development of systemic inflammatory response syndrome (SIRS) not only due to the cardiovascular surgery itself but also due to the exposure of the patient to the adverse effect of CPB[20, 21]. The main reason is that the aorta needs to be blocked during CPB, and blood dilution is performed. Microthrombosis will inevitably be generated during CPB. Harmful substances will also be produced after low temperature circulation and rewarming. The above factors have an impact on cerebral blood perfusion, Resulting in ischemic and hypoxic changes in brain tissue. The results of this study showed that postoperative mechanical ventilation time is an independent risk factor for the occurrence of postoperative delirium. The longer the mechanical ventilation time, the higher the incidence of delirium. In recent years, a large number of studies have shown that mechanical ventilation is a related risk factor for delirium[2]. While mechanical ventilation exerts its therapeutic effects, it also changes the patient’s normal hemodynamics and respiratory physiology, and is likely to cause extreme physical and psychological discomfort for the patient. In addition, mechanically ventilated patients are also prone to sleep disorders, Patients who are mechanically ventilated have more fragmented and daytime sleep and reduced sleep efficiency than patients who are not mechanically ventilated[22]. In addition, the inclusion of sleep disturbance to the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition in its constellation of symptoms used in diagnosing delirium has increased awareness of the link between sleep and delirium[22]. Patients undergoing cardiovascular surgery routinely require ventilator-assisted ventilation, which leads to a high incidence of postoperative delirium. In the off-line assessment process, the patient has delirium and cannot cooperate with the assessment, which makes it difficult to make accurate off-line decisions. At present, there is no uniform standard in the academic circles for PMV(prolonged mechanical ventilation, PMV). PMV is generally defined as mechanical ventilation for patients after cardiac surgery for more than 24 hours[23, 24]. Therefore, if the ventilator cannot be evacuated within 24 hours after cardiac surgery, It should arouse the high attention of medical staff and take related measures to shorten the time of mechanical ventilation. At present, the ABCDEF clustered delirium prevention strategy proposed by the 2017 National Critical Care Medicine Conference[25] and eCASH strategy[26] are more commonly used. The results of this study showed that postoperative hypernatremia is a high-risk factor for postoperative delirium. Hypernatremia refers to electrolyte disorders with a blood sodium concentration of >145 mmol/L. The study by Hong Liang[27] showed that hypernatremia increases the probability of postoperative delirium, which is consistent with our research results. Theologou et al[28] also showed that the risk of developing POD was associated with prolonged endotracheal intubation and prolonged ICU stay, along with peaked urea, neutrophil-to-lymphocyte ratio, creatinine, and sodium levels. The finding might suggest that an inadequate reaction of the immune system may play a role in the pathogenesis of delirium[14]. Therefore, medical staff should correct the patients’ hypernatremia in time and maintain a stable internal environment.
The Nomogram model constructed in this study was used to score patients after cardiovascular surgery, and the risk of delirium in the patient was calculated to achieve individualized prediction. For example: the patient is 70 years old, draw a vertical line from the point on the age scoring axis to the Point axis, and the corresponding score for the patient is 22 points. The scores of other items are measured in the same way, and the CPB duration, is 150 minutes (Score=10 points), postoperative Serum Sodium is 145mmol/L (score=25 points), postoperative MV is 50 minutes (score=15 points), then the total score of the nomogram=22+10+25+15=72points, the corresponding risk of delirium is 0.72, that is, the patient has a 72% risk of developing delirium. The higher the risk of patients, the more attention should be paid to medical staff, and the patients should be actively intervened. When the patient cannot be evacuated from the ventilator within 24 hours, the mechanical ventilation time is prolonged, or the serum sodium concentration changes, medical staff should dynamically evaluate and take intervention measures to reduce injuries, so as to reduce the risk of delirium and improve the prognosis.