| BackgroundAmong the various types of postoperative organ injuries,acute kidney injury（AKI）is particularly prevalent in 5%to 20%of patients undergoing major abdominal surgery and in 10%to 40%of high-risk patients with hepatic resection surgery.Previous studies have confirmed AKI as an independent contributor to peri-and postoperative morbidity（infection and prolonged hospital stay）and mortality in both cardiac and non-cardiac surgeries,and may also contribute to the development of advanced chronic kidney disease requiring long-term renal replacement therapy,involving substantial healthcare burden.Perioperatively,numerous events can occur that each by itself may impair renal function:advanced age,previous comorbidity,exposure to nephrotoxic medicaments and contrast agents,ischemia-reperfusion injury,hypotension and hypovolemia,blood transfusion,infection,and inflammatory response.More than 20 million older patients in China are undergoing elective surgery every year,accounting for approximately 25%of surgical procedures.With the rapid advances in anesthetic and surgical techniques,more and more older patients are accessible to surgical excision for hepatobiliary diseases.In the older population,however,the incidence of postoperative AKI is significantly higher as the microstructural and functional changes with aging,and compensatory capacity of the kidney decreases due to the comorbid hypertension,diabetes,and vascular sclerosis.It is thus significantly important to identify those patients at high risk to develop postoperative AKI to optimize perioperative prevention and protection strategies.Despite the improved diagnosis of AKI with the elaboration and dissemination of new diagnostic criteria,more efforts to prevent the development of postoperative AKI are needed.However,given that a detectable increase in the levels of serum creatinine does not immediately follow the onset of AKI,serum creatinine levels alone are of limited value for the early identification of AKI risks.Near-infrared spectroscopy（NIRS）is a new non-invasive technique that continuously monitors regional oxygen saturation by measuring the relative concentrations of oxygenated and deoxygenated hemoglobin within a local tissue area.The results of several observational studies indicate that renal desaturation during and after cardiac surgery with cardiopulmonary bypass is associated with worse renal outcomes,indicating the necessity of maintaining stable renal oxygen saturation.Patients undergoing liver resection are at high risk of developing postoperative AKI due to the increased risk of ischemia and hypoxia resulted from the long operation time,extensive trauma and blood loss,requirement for blood transfusion and hepatic vascular clamping.Intraoperative real-time monitoring of renal oxygen saturation allows early detection of renal hypoxia.More importantly,application of this method to the intraoperative period could provide a pathway for the development of interventions by anesthesiologists to prevent intraoperative renal hypoxia and thus potentially postoperative AKI.There are currently not enough studies on hepatic resection-related AKI risk factors and predictive nomogram,and yet to the best of our knowledge no relevant literature has been available regarding renal oxygen monitoring in this group of patients.Therefore,the present study aimed to explore the potential risk predictors based on retrospective analysis,and prospectively investigate the effect of intraoperative renal desaturation in the development of postoperative AKI in a cohort study,thus to provide theoretical bases and practical evidence for early identification of patients at high risk of AKI and optimization of perioperative strategies for renal protection.Objective1.In this retrospective analysis,we aim to investigate the incidence and perioperative risk factors of postoperative AKI in older patients undergoing liver resection based on the retrospective database,and develop a predictive nomogram and summary risk score model.2.The prospective cohort study aims to determine whether intraoperative renal desaturation as accessed by near-infrared spectroscopy,is associated with postoperative AKI in older patients undergoing liver resection.Methods1.A retrospective observational study was conducted involving data from 843 older patients（≥65 years）scheduled for liver resection at our center between January 2012 and July2019.The data were randomly divided into training（n=599）and validation（n=244）datasets with a spit ratio of 70%and 30%.The training cohort was used to construct a predictive nomogram for postoperative AKI with the multivariable logistic regression model which was then evaluated by the validation cohort.The receiver operating characteristic curve analysis and Hosmer-Lemeshow goodness-of-fit test were used to evaluate the discrimination and accuracy of the prediction.The decision curve analysis was used to assess the model’s clinical utility.To promote the clinical application of the nomogram,a summary risk score system based on the results of the multivariable logistic model was also constructed for identifying postoperative AKI patients.The predictors selected from the multivariable logistic model were dichotomized and counted.Continuous variables were divided into two subgroups with good or poor prediction based on the cut-off values determined by the receiver operating characteristic curve analyses.One point or zero was assigned to each of the predictors to construct the summary risk score model to predict the risk probability of AKI.2.In the multicenter prospective cohort study,157 older patients（≥60 years）undergoing elective open hepatectomy were enrolled in the First Medical Center of Chinese PLA General Hospital and the Beijing Tsinghua Changguang Hospital between September 2020 and October2021,among which 109 were male and 48 were female,with the median age 66（60-70）.Intraoperative renal regional oxygen saturation was bilaterally and continuously monitored throughout the anesthetic and surgical procedure.The exposure was intraoperative renal desaturation,defined as an at least 20%decrease in renal oxygen saturation from baseline value for at least 30 seconds.Patients were divided into two groups:patients without intraoperative renal desaturation and patients with intraoperative renal desaturation.The primary outcome was postoperative AKI according to the Kidney Disease:Improving Global Outcomes criteria,namely an absolute increase in serum creatinine of 26.5μmol·L-1 within 48 hours or a 1.5-fold increase from preoperative baseline within seven days after surgery.The association between intraoperative renal desaturation and postoperative AKI was evaluated by multivariable logistic regression adjusted for potential confounding factors.Based on the results of multivariable logistic regression,the predictive performance of intraoperative renal desaturation model and hypotension model for predicting postoperative AKI were evaluated and compared.Results1.（1）In retrospective analysis,postoperative AKI occurred in 155（18.4%）patients and was highly associated with in-hospital morality（5.2 vs.0.7%,P<0.001）.（2）The six predictors selected from the multivariable logistic regression and assembled into the nomogram included age,preexisting chronic kidney disease,intraoperative hepatic vascular clamping,estimated blood loss and red blood cells transfusion,and non-steroidal anti-inflammatory drugs usage.（3）The predictive nomogram performed well in terms of discrimination,with the areas under the receiver operating characteristic curves and 95%confidence interval in training and validation datasets 0.73（0.68–0.78）and 0.71（0.63–0.80）,respectively.（4）The nomogram was well-calibrated with the Hosmer-Lemeshow chi-square values of 9.68（P=0.47）and 3.86（P=0.87）in the training and validation datasets,respectively.（5）Decision curve analysis demonstrated a significant clinical benefit within 10%to 40%threshold probability.（6）The summary risk score calculated as the sum of points from the six variables（one point for each variable）from the multivariable logistic regression model performed as well as the nomogram in identifying the risk of AKI,with the area under the receiver operating characteristic curve and 95%confidence interval 0.71（0.66–0.76）.2.（1）In the prospective cohort study,baseline renal oxygen saturation was 83（74–89）%.Renal desaturation occurred in 70 of 157 patients,with the incidence rate of 44.6%.（2）The overall incidence of postoperative AKI was 14.6%（23 in 157）.Postoperative AKI was observed in 22.9%（16/70）of patients with,and 8.0%（7/87）of patients without intraoperative renal desaturation.（3）Intraoperative renal desaturation was associated with an increased likelihood of developing postoperative AKI（odds ratio 3.39,95%confidence interval 1.35-9.32,P=0.012）in univariable logistic regression analysis.（4）The association between renal desaturation and AKI remained significant after further adjustments for potential confounders（odds ratio 3.61,95%confidence interval 1.07-13.42,P=0.043）.（5）Compared with prediction with hypotension model,intraoperative renal desaturation model exhibited a better goodness of fit（likelihood ratio test chi-square value 4.379,P<0.001）,and a higher net benefit within 10%to 40%threshold probability.Conclusions1.Postoperative AKI occurred in 15%-18%of older patients undergoing liver resection;2.Advanced age,declined preoperative renal function,intraoperative hepatic vascular clamping,blood loss and red blood cells transfusion,and non-steroidal anti-inflammatory drugs usage are independent predictors for postoperative AKI,with potential application in early identification of individuals with high risk of developing AKI;3.Intraoperative renal desaturation occurs frequently in older patients and is associated with greater risk of postoperative AKI. |
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