Relationship Between Renal Venous Return and Prognosis of Renal Function in Patients With AKI in ICU
Condition: Renal Venous Return
Study type: Observational

Summary: 
      A single-center prospective longitudinal observational study was carried out. Assessments
      were made on Days 1, 3, 5, and 7 after ICU admission in 90 patients with sepsis AKI, and 19
      patients with septic without AKI only made assessments on Day 1. The primary outcome was CVP
      obtained at the time of renal ultrasonography. The association among RVF patterns, IRVF
      patterns, and CVP was examined using Student's t-test, and that with composite outcomes was
      assessed using a generalized estimating equation analysis, to account for intra-individual
      correlations.
    

Detailed description: 
      The prospective observational study was conducted at the ICU in China. The study was approved
      by the institutional review board of Peking Union Medical College Hospital (approval number,
      I-23PJ1176). All procedures were performed in accordance with the ethical standards of the
      local ethics committee on human experimentation and with the Helsinki Declaration of 1975.

      Study participants

      A single-center prospective longitudinal observational study is carried out at a tertiary
      critical care unit in China. Serial assessments were made of the renal RVF, IRVF, and CVP at
      4-time points: Day one (D1) within 24 h of ICU admission, D1 + 48 h (D3), D1 + 96h (D5) and
      D1 + 144h (D7). Only adult patients (> 18 years) were included. AKI was staged using KDIGO
      criteria. Common to AKI research, the baseline creatinine value may not be known, and
      therefore defining AKI biochemically is not always possible. For those who had AKI defined
      using creatinine, we used the lowest value of any form within the 12 months prior to
      admission as a baseline value. If no preadmission creatinine was available, the lowest value
      the creatinine returned to after the resolution of acute illness was used. Failing all the
      above and if AKI could not be staged by other criteria, the admission creatinine was used as
      the baseline value. We excluded patients who (i) were on maintenance dialysis for chronic
      renal failure, (ii) were pregnant, (iii) had any ureteral obstructions because these affect
      the IRVF waveforms, and (vi) had earlier participation in this study.

      Renal ultrasonography

      The technical aspects of renal ultrasonography are as follows. Using a sector transducer, the
      right kidney in the left lateral supine position. Color Doppler images were used to determine
      a target renal and intrarenal vein. The RVF waveforms (the flow away from the transducer
      below the baseline) were classified into four waveform patterns: continuous or discontinuous
      (inclusion Biphasic continuous, Biphasic separated, and Monophasic). Specifically, a
      continuous pattern corresponded to the presence of continuous, uninterrupted venous flow
      below the baseline throughout the cardiac cycle, whereas the discontinuous pattern was a
      group of patterns that had at least one phase with zero velocity in venous flow during a
      cardiac cycle. The venous impedance index (VII), that is, the proportion of reduction in
      venous flow from its peak velocity (very low [0.2] in healthy subjects), was calculated as
      the peak maximum flow velocity minus the maximum flow velocity at the nadir in veins divided
      by the maximum flow velocity. The renal venous stasis index (RVSI) was calculated as the
      index cardiac cycle time minus the renal venous flow time divided by the index cardiac cycle
      time. In patients with sinus rhythm, we measured all indices over three cardiac cycles at the
      end of expiration and averaged them. In patients with atrial fibrillation, we measured the
      indices at a cardiac cycle where two preceding cardiac cycles had nearly equal durations.
      Echocardiography was performed at the bedside in the ICU. Meantime, CVP was measured.
    

Observational model: Other
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Only adult patients (> 18 years) were included. AKI was staged using KDIGO criteria. Common
        to AKI research, the baseline creatinine value may not be known and therefore defining AKI
        biochemically is not always possible. For those who had AKI defined using creatinine, we
        used the lowest value of any form within the 12 months prior to admission as a baseline
        value. If no preadmission creatinine was available, the lowest value the creatinine
        returned to after the resolution of acute illness was used. Failing all the above and if
        AKI could not be staged by other criteria, the admission creatinine was used as the
        baseline value. We excluded patients who (i) were on maintenance dialysis for chronic renal
        failure, (ii) were pregnant, (iii) had any ureteral obstructions because these affect the
        IRVF waveforms, and (vi) had earlier participation in this study.
      
Keywords: Ultrasonography; Renal congestion; Renal venous flow; Intrarenal venous flow; Acute kidney injury