Prediction Value Of Renal Color Doppler To Assess Acute Kidney Injury For Critically Ill Patients

Objective: To assess whether renal color Doppler can early predict acute kidney injury(AKI)for critically ill patients by monitoring renal blood flow(RBF)level and renal resistive index(RRI),compared with novel renal injury biomarkers,such as serum Cystatin C(CysC),urinary tissue inhibitor of metalloproteinase 2(TIMP-2)and insulin-like growth factor-binding protein 7(IGFBP-7).Methods: We included patients with AKI defined by the Kidney Disease: Improving Global Outcomes(KDIGO)criteria and only with risk factors(SOFA score: Respiration≥2 and/or Cardiovascular≥2)but without AKI when admitted to the general intensive care unit(ICU)at the Forth Hospital of Hebei Medical University from June 2015 to January 2016.We took the urine and blood samples of all patients within 1 hour of inclusion to the study and the color Doppler at the same time.After centrifugation at 2000 rpm for 10 min,the supernatant urine was stored at-80℃.Blood samples were taken to the biochemical laboratory.Serum creatinine was measured with Jaffe’s assay,and Serum CysC was measured with a particle-enhanced turbidimetric immunoassay.Using the Vivid i portable color Doppler,we detect the cardiac output(CO)by measuring left ventricular outflow tract velocity time integral(VTI)and pulmonary artery systolic pressure(PASP).The probe was put on the right side of the patient’s abdomen to obtain a clear image of the right kidney.An interlobar or arcuate artery was selected,and the measurements were obtained.The main indexes included RBF level,RRI and corrected RRI(cRI),which were calculated using the following equations,cRI =(observed RI – 0.0026 × [80 – observed HR]).After collection of all urine samples,urinary [TIMP-2]×[IGFBP7] was quantified by enzyme-linked immuno sorbent assay.The lowest creatinine level obtained within three months prior to ICU admission was used as baseline for the KDIGO classification.When pre-ICU creatinine was lacking,it was set as the lowest value after renal function improvement imputed using the MDRD formula,assuming an essentially normal baseline glomerular filtration rate of 75 ml/min/1.73 m2.Transient AKI was defined as AKI with a cause of renal hypoperfusion and recovery within 3 days after diagnosis of AKI.Recovery from AKI was defined as urine output normalization and/or serum creatinine decrease by 50% and/or serum creatinine normalization to its measured or estimated baseline level.Persistent AKI was defined as persistent serum creatinine rise or oliguria after 3 days.Results:1 The inclusion process and groups in this studyWe screened 153 patients and included 108 patients at last.Among the 30 patients with AKI when admitted to ICU,20 patients were transient AKI,and 10 patients were persistent AKI.Of 78 patients only with risk factors without AKI when admitted to ICU,40 patients developed to AKI within 24 hours.Of these,28 patients were transient AKI,and 12 patients were persistent AKI.2 The main causes of the patients admitted to the studyThe main causes of the patients admitted to the study were septic shock,acute respiratory distress syndrome(ARDS),operative stress,cardiogenic shock,cardiopulmonary resuscitation(CPR)and pulmonary embolism(PE).The number of AKI patients with these causes was 29(41.4%),15(21.4%),10(14.3%),7(10%),6(8.6%),3(4.3%),respectively.The number of no AKI patients with these causes was 11(28.9%),7(18.4%),10(26.3%),4(10.5%),2(5.4%),4(10.5%),respectively.There was no significant statistic difference between AKI and no AKI groups in the main causes(P=0.168).There also was no difference between transient AKI and persistent AKI groups(P=0.687).The number of transient AKI patients with these causes was 20(41.7%),9(18.8%),7(14.6%),5(10.4%),4(8.3%),3(6.2%),respectively.And the number of persistent AKI patients with these causes was 9(40.9%),6(27.3%),3(13.6%),2(9.1%),2(9.1%),0(0%),respectively.3 Comparison of the stage of AKI between transient AKI and persistent AKI groupsThe number of stage 1,2,3 AKI in the AKI group was 27(38.6%),11(15.7%),32(45.7%),respectively.The number of stage 1,2,3 AKI in the transient AKI group was 25(52.1%),9(18.7%),14(29.2%),respectively.In addition,the number of stage 1,2,3 AKI in the persistent AKI group was 2(9.1%),2(9.1%),18(81.8%),respectively.Persistent AKI group had less stage 1 patients(P =0.001)and more stage 3 patients(P <0.001).4 Comparison of epidemiologic characteristics among transient AKI,persistent AKI and no AKI groupsThere was no difference in the characteristics such as gender,age,height,weight,kidney size,baseline serum creatinine value among transient AKI,persistent AKI and no AKI groups(P >0.05).Compared with transient AKI group,persistent AKI group had more diabetes patients(P =0.001)and less cancer patients(P =0.011).5 Comparison of clinical data between AKI and no AKI groupsCompared with no AKI patients,AKI patients had higher APACHE Ⅱ score(P=0.024),higher PASP(P=0.035),higher dose of norepinephrine(P=0.001),even though the mean arterial pressure had no difference(P=0.058).The level of urine [TIMP-2]×[IGFBP7] and serum CysC(P<0.001)and RRI(P=0.009)was higher,RBF level(P=0.003)was lower among AKI patients than no AKI patients,but there was no difference in cRI(P=0.219).Among the patients with risk factors but without AKI at ICU admition,compared with no AKI patients,patients who developed AKI afterwards had higher volume status(P<0.001)and higher mean dose of NE(P=0.027)within 24 hours.Only the urine [TIMP-2]×[IGFBP7](P=0.018,OR=250524.4)and serum CysC(P=0.005,OR=22.8)will influence the result of AKI within 24 hours(R~2=0.654).6 Comparison of clinical data between transient AKI and persistent AKI groupsCompared with transient AKI patients,persistent AKI patients had lower temperature(P=0.002),higher level of serum CysC(P=0.001),higher rate of CRRT(P=0.003)and lower volume status within 3 days(P=0.020).Other parameters had no statistical differences.7 The assessment of prediction value for AKI within 24 hoursThe AUC of urine [TIMP-2]×[IGFBP7],serum Cys C,RBF level and RRI of the predictive power for AKI within 24 hours was 0.766(95%CI,0.675-0.857;P<0.001),0.783(95%CI,0.699-0.867;P<0.001),0.659(95%CI,0.561-0.747;P<0.001),0.669(95%CI,0.572-0.756;P=0.002),respectively.The cutoff value of urine [TIMP-2]×[IGFBP7] and serum CysC was 0.295(ng/ml)2/1000(sensitivity 62.9%,specificity 79.0%),1.12mg/L(sensitivity 60.0%,specificity 94.7%),respectively.Compared with RBF level,serum CysC had higher accuracy of prediction value for AKI within 24 hours(P=0.038),and there had no difference among other parameters.8 The assessment of prediction value for persistent AKIThe AUC of serum CysC of the predictive power for persistent AKI was 0.720(95%CI,0.600-0.821;P=0.001),and the cutoff value was 1.51mg/L(sensitivity 68.2%,specificity 77.1%).Conclusions:1 AKI patients had higher level of urine [TIMP-2]×[IGFBP7],serum CysC and RRI,lower RBF level.Persistent AKI patients had higher level of serum CysC.2 Urine [TIMP-2]×[IGFBP7] and serum CysC could be the sensible tools to predict AKI within 24 hours,and serum CysC could be the sensible tool to predict persistent AKI.3 Compared with serum CysC,the parameters of color Doppler such as the RBF level had lower prediction value for AKI.