Lower Preoperative Serum Uric Acid May Be An Independent Risk Factor For Postoperative Delirium In Older Patients Undergoing Hip Fracture Surgery:a 1:2 Matched Case-control Study

BACKGROUNDPostoperative delirium(POD)is a common complication in older patients undergoing hip surgery.The incidence of POD is as high as 53%.POD is associated with various shortand long-term outcomes and affects the quality of life.The pathogenesis of POD is still unclear.Oxidative stress and neuroinflammation in the brain may play a key role in the onset and progression of POD.The treatment for POD is unsatisfactory.Therefore,early identification of risk factors for POD is critical for high-risk patients.As an important endogenous antioxidant in the human body,serum uric acid(sUA)is a research hotspot in the field of neurodegenerative diseases.It plays a neuroprotective role in a variety of neurodegenerative diseases through its antioxidant properties.However,it is unclear whether lower preoperative sUA levels are associated with the development of POD after hip surgery.Therefore,this study aims to assess the association of lower preoperative sUA levels in patients with POD during hospitalization.PURPOSE1.To analyze the risk factors for POD in older patients undergoing hip surgery;2.To explore the association between preoperative sUA levels and POD,and to evaluate its predictive value in older patients.METHODSThis is a 1:2 matched case-control study that included 141 older patients(≥65 years)who underwent hip surgery.POD was diagnosed using the Diagnostic and Statistical Manual of Mental Disorders,Fifth Edition(DSM-V).Patients diagnosed with POD(cases)were matched 1:2 with patients without POD(controls)based on age and sex.The association between preoperative sUA and POD was analyzed by multivariable conditional Logistic regression.Receiver operating characteristics(ROC)were used to identify predictors of POD.RESULTS1.The incidence of POD in older patients undergoing hip surgery was 15.8%.A total of 141 patients were included in the study,of whom 114(80.85%)were female and 27(19.15%)were male.The age of the POD group was 85.00(81.00,90.00)years old,and that of the non-POD group was 84.50(81.00,89.00)years old.2.A higher proportion of patients in the POD group had a history of cerebrovascular diseases,including stroke and transient ischemic attack[16(34.04%)vs.15(15.96%),P=0.015].The preoperative neutrophil-lymphocyte ratio(NLR)was higher in the POD group than in the non-POD group[5.20(3.30,8.16)vs.3.93(2.83,5.32),P=0.001].On the contrary,the preoperative sUA levels in the POD group were lower than that in the non-POD group(219.64±71.21μmol/L vs.271.06±74.89μmol/L,P<0.001),with a difference of 51.43(95%CI:25.40-77.46)μmol/L.3.In the univariate conditional Logistic regression analysis,the history of cerebrovascular disease(OR=2.456,95%CI:1.121-5.378,P=0.025)and high NLR(OR=1.320,95%CI:1.119-1.556,P=0.001)were risk factors for POD in older patients undergoing hip surgery.In contrast,preoperative sUA(OR=0.990,95%CI:0.984-0.996,P=0.001)was a protective factor for POD.4.To avoid overestimation,a conservative approach was used:all variables with P<0.20 on univariate analyses(including the history of cerebrovascular disease and coronary heart disease,preoperative sUA level,intraoperative fluid supplement,anesthesia time,NLR,and hemoglobin concentration)were included in the multivariate conditional Logistic regression analysis,which showed that lower preoperative sUA(OR=0.989,95%CI:0.982-0.996,P=0.003),higher NLR(OR=1.319,95%CI:1.101-1.580,P=0.003),and lower hemoglobin concentration(OR=0.969,95%CI:0.944-0.994,P=0.014)were independent risk factors for POD in older patients undergoing hip surgery.5.ROC analysis showed that the area under curve(AUC)of preoperative sUA was 0.68(95%CI:0.58-0.77).The cutoff value was 241.00 μmol/L,with sensitivity and specificity of 66.0%and 60.6%,respectively.The AUC for NLR was 0.67(95%CI:0.57-0.76).The cutoff value of NLR was 4.54,with sensitivity and specificity of 63.8%and 62.8%,respectively.The AUC for hemoglobin concentration was 0.60(95%CI:0.50-0.70).The cutoff value was 107.5g/dL,with the sensitivity and specificity of 59.6%.The AUC for the three-item models including preoperative sUA,NLR,and hemoglobin concentration was 0.78(95%CI:0.70-0.85).6.Compared with the non-POD group,the patients in the POD group had no significant differences in hypostatic pneumonia and deep venous thrombosis(P>0.05),but the length of hospitalization was prolonged(9[8,12]days vs.8[7,9]days,P<0.001).CONCLUSIONLower preoperative sUA level may be an independent risk factor for POD after adjustment for possible confounding factors.Preoperative sUA levels have predictive value for POD.Higher NLR and lower hemoglobin concentration are also independent risk factors for POD in older patients undergoing hip surgery.The length of hospitalization in patients with POD is prolonged.However,large prospective studies are needed to further confirm these findings.