Ultrasound examination as a method of early “bedside” diagnosis of acute kidney injury in geriatric patients after urgent abdominal surgery

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Geriatric patients are particularly vulnerable to the development of postoperative complications, one of which is acute kidney injury (AKI). Early diagnosis of AKI is an important component of the effectiveness of its prevention and treatment. It is believed that ultrasound examination of renal blood flow may be a promising method for bedside diagnosis of AKI.
 The aim is to evaluate the predictive value of renal resistance index (RRI) and semiquantitative renal perfusion (SQP) as methods for early diagnosis of AKI in geriatric patients after urgent abdominal surgery.
 Materials and methods. A prospective single-center study included 40 patients (72.5 (65; 81.5) y. o.) who were assessed for the risk of development, the presence and stage of AKI, and additionally measured hemodynamic parameters, intra-abdominal pressure (IAP), and abdominal perfusion pressure (APP). Renal resistance index (RRI) and semi-quantitative renal perfusion score (SQP) were determined using Doppler ultrasound (ultrasound probe CH-6, SIEMENS, Acuson Antares). Statistical analysis was performed using the STATISTICA for Windows 13 program (StatSoftInc., No. JPZ804I382130ARCN10-J).
 Results. In the postoperative period, AKI developed in 26 patients (65%). Compared with patients without AKI, they had a 14% lower level of mean arterial pressure (MAP) (p=0.008), as well as an average of 4 mmHg higher IAP (p=0.005) and significantly lower APP (p=0.0348). Correlation analysis revealed a weak relationship between the values of MAP, IAP, APP and the development of AKI (r=0.34, r=0.41, r=0.392, respectively, p˂0.05).
 Patients with AKI had a 13.9% higher RRI than patients without AKI (0.75 (0.72; 0.81) r.u. vs 0.66 (0.61; 0.69) r.u., respectively, p=0.000001), however, the degree of SQP of the kidneys did not differ significantly between the groups (p=0.636). The correlation between the RRI and the development of AKI was of moderate strength (r=0.57, p˂0.05). MAP, IAP, and APP were significantly very weakly correlated with RRI (r=0.34; r=0.41, r=0.392, respectively, p˂0.05). ROC analysis showed that RRI>0.71 r.u. is the threshold level for AKI with 87.2% sensitivity and 73.5% specificity, and it has a high predictive value (area under the curve AUC 0.868 (p<0.0001)).
 Conclusions. High RRI values are associated with AKI in geriatric patients after urgent abdominal surgery. RRI may be a bedside diagnostic tool for AKI, in contrast to renal SQP, which has shown no predictive value.