Analysis Of Risk Factors For Postoperative Delirium In Frail Elderly Patients After Cardiac Surgery And Development Of A Prediction Model

Objective To identify the risk factors of postoperative delirium（POD）in frail elderly patients after cardiac surgery and develop a ROC prediction model and Pearson correlation analyze model.Methods This is an observational study.Patients were assessed preoperatively according to the Frailty index scale（FI）and frailty was defined as FI≥0.25;pre-frailty was defined as FI 0.09-0.25;non-frailty was defined as FI≤0.08.130 patients aged 65yr and older scheduled for cardiac surgery with cardio-pulmonary bypass（CPB）were included in this observational study.Clinical information such as gender,age,body mass index（BMI）,Mini-mental state examination（MMSE）score,Frailty index scale,past medical history,results of preoperative laboratory tests,the length of CPB,the length of aortic cross-clamping,the length of mechanical ventilation and the length of operation were recorded.Near infrared spectroscopy（NIRS）was used to monitor cerebral oxygen saturation（r SO₂）.The mean values of r SO₂ were recorded at 1 day before operation（T₀）,5 minutes after entering the operating room（T₁）,before CPB（T₂）,before aortic cross clamping（T₃）,after aortic cross clamping（T₄）,after CPB（T₅）and before leaving the operating room（T₆）.r SO₂baseline(r SO_{2 baseline}),lowest intraoperative r SO₂ value before,during and after CPB(CPB₁r SO_{2 lowest},CPB₂r SO_{2 lowest},CPB₃r SO_{2 lowest}),the greatest intraoperative r SO₂ decrease from the baseline value before,during and after CPB（CPB1r SO2 decrease,CPB2r SO2 decrease,CPB3r SO2 decrease）were recorded.Delirium was assessed on 1d,3d,5d and 7d after operation.According to the occurrence of POD within 7 days after surgery,patients were divided into POD group and non-POD group.Risk factors for POD were analyzed by logistic regression.The receiver operating characteristic（ROC）curve was drawn to evaluate the accuracy of the related risk factors.Pearson correlation was used to analyze the relationship between cerebral oxygen saturation and the incidence of POD in frail elderly patients after cardiac surgery.Results A total of 130 patients were enrolled in this study,including 76 men（58.5%）,54 women（41.5%）.Aged between 65 and 87 years.There were 32 cases in POD group and 98 cases in non-POD group.The incidence of POD was 24.6%.The results of univariate analysis showed that,compared with the non-POD group,there were significant differences in ASA classification,preoperative MMSE score,Frailty index score,r SO_2baseline,CPB₁r SO_2lowest,CPB₂r SO_2decrease,hyperlipidemia,diabetes,cerebrovascular disease,hemoglobin,plasma albumin,the length of CPB and the length of operation in POD group（P<0.05）.Multivariate logistic regression analysis showed that the FI（OR=2.602;95%CI1.073～3.541;P<0.001）,CPB₂r SO_{2 decrease}（OR=1.098;95%CI1.036～1.164;P=0.002）,CPB₂r SO_{2 lowest}（OR=0.89;95%CI0.812～0.976;P=0.013）and the length of operation（OR=1.013;95%CI1.001～1.026;P=0.03）were independent risk factors for POD.The results of ROC curve analysis showed that FI>0.27（AUC=0.751,95%CI 0.649～0.852,sensitivity 65.6%,specificity 80.6%）,CPB₂r SO_{2 decrease}>11.2%（AUC=0.655,95%CI 0.533-0.778,sensitivity 68.9%,specificity 62.9%）and the length of operation>237.5 min（AUC=0.751,95%CI0.652-0.849,sensitivity 62.5%,specificity 78.6%）had a predictive value for the occurrence of POD.Pearson correlation analysis showed a linear correlation between CPB₂r SO_{2 decrease} and POD incidence（R²=0.325,F=6.216,P<0.001）.The incidence of postoperative delirium increased by 2.9%for every 1%increase in the greatest cerebral oxygen saturation decrease from the baseline value during cardiac surgery in frail elderly patients.Conclusion Frailty index score,CPB₂rSO_{2 decrease},CPB₂r SO_{2 lowest} and the length of operation were independent risk factors for the development of postoperative delirium in frail elderly patients after cardiac surgery.Frailty index score,CPB₂r SO_{2 decrease} and the length of operation were valuable to predict the occurrence of POD in frail elderly patients after cardiac surgery.The incidence of postoperative delirium increased by 2.9%for every 1%increase in the greatest cerebral oxygen saturation decrease from the baseline value during cardiac surgery in frail elderly patients.