Renal venous flow in different regions of the kidney are different and reflecting different etiologies of venous reflux disorders in septic acute kidney injury: a prospective cohort study

Abstract

Background: Acute kidney injury (AKI) is a frequent complication of sepsis. While impaired renal venous reflux indicates renal congestion, the relationship between AKI outcomes and hemodynamic parameters remains debated. This study aimed to investigate the utility of renal venous flow patterns in various regions of septic patients and to explore the association between hemodynamic parameters and renal function prognosis.

Methods: In this single-center, prospective longitudinal study, adult sepsis patients diagnosed with AKI were enrolled. Renal ultrasonography was performed within 24 h of ICU admission (D1), then repeated at D3 and D5. Patterns of proximal renal venous flow (PRVF) and intrarenal venous flow (IRVF) patterns were confirmed by two blinded sonographers. Kaplan-Meier survival analysis was used to evaluate renal prognosis, and cumulative incidence curves were generated for renal function recovery time.

Results: The study included 96 septic patients. Inconsistencies between PRVF and IRVF patterns occurred in 31.9%, with PRVF patterns being more severe in 88% of these. A relatively strong correlation was observed between PRVF and CVP, but this trend was less evident in IRVF. For RVSI of PRVF at ICU admission, the AUC to predict 28-day renal function prognosis was 0.626 (95% CI 0.502-0.750, P = 0.044), while combined PRVF and IRVF had a higher predictive ability (AUC 0.687, 95% CI 0.574-0.801, P = 0.003). The 28-day renal prognosis was poorer in the PRVF 5-day non-improvement group compared to the 3-day improvement group (P = 0.001) and 5-day improvement group (P = 0.012). Patients with a persistent monophasic PRVF pattern within 5 days had a worse prognosis than the non-monophasic group (P = 0.005).

Conclusions: Our study reveals that patterns of PRVF and IRVF are not entirely congruent, stepwise evaluation is useful in determining the intervention site for renal vein reflux disorders. Combined PRVF and IRVF had a higher predictive ability for 28-day renal function prognosis. Early improvement in renal venous congestion is crucial for better renal function prognosis. This study is registered with ClinicalTrials.gov, number NTC06159010. Retrospectively registered 28 November 2023.

Keywords: Acute kidney injury; Intrarenal venous flow; Proximal renal venous flow; Renal congestion; Sepsis.

Fig. 1

Different types of renal venous reflux status. a Sampling site: the proximal renal venous; b sampling site: the intrarenal venous; c continuous pattern; d discontinuous pulsatile pattern; e discontinuous biphasic pattern; f discontinuous monophasic pattern. The renal venous stasis index (RVSI) was calculated as the index cardiac cycle time ($t_1$) minus the renal venous flow time ($t_2$) divided by the index cardiac cycle time

Fig. 2

Flow diagram of participants through the study. TAPSE tricuspid annular plane systolic excursion, LVOT VTI velocity–time integral of the left ventricular outflow tract, MAPSE mitral annular plane systolic excursion, P_(V–A) CO₂ central venous-to-arterial carbon dioxide difference, ScvO₂ central venous oxygen saturation, CVP central venous pressure, MAP mean arterial pressure

Fig. 3

Renal venous reflux patterns of results for each examination (96 patients, 288 examinations). a Number of examinations in four different groups in PRVF and IRVF patterns, separately; b number of examinations in six different groups combined PRVF and IRVF patterns. PRVF, proximal renal venous flow; IRVF, intrarenal venous flow. PRVF < IRVF, meant obstruction of PRVF patterns were lighter than that of IRVF patterns. PRVF > IRVF, meant obstruction of PRVF patterns were heavier than that of IRVF patterns

Fig. 4

Data distribution for clinical parameters throughout the study. a RVSI in different PRVF patterns. b RVSI in different IRVF patterns. c CVP in different PRVF patterns. d CVP in different IRVF patterns. RVSI renal venous stasis index, PRVF proximal renal venous flow, IRVF intrarenal venous flow, CVP central venous pressure

Fig. 5

ROC for the recovery from acute kidney injury. RVSI renal venous stasis index, PRVF proximal renal venous flow, IRVF intrarenal venous flow pattern

Fig. 6

Grouping of proximal renal venous flow (PRVF) pattern is based on the flowchart. a Grouping of time to improvement in PRVF patterns; b grouping of whether the PRVF pattern is monophasic and its duration time

Fig. 7

Kaplan–Meier curves for the recovery from acute kidney injury. a, b Non-recovery from acute kidney injury in four groups in terms of proximal renal venous flow (PRVF) pattern and intrarenal venous flow pattern (IRVF). P value: compared to discontinuous monophasic pattern. c Renal prognosis in different groups in terms of PRVF. P value: compared to 5-day non-improvement group. d Duration time of the discontinuous monophasic pattern of PRVF. P value: compared to 5-day monophasic group. Nonrecovery from AKI was defined as the last available creatinine during the first 28 days of hospitalization remained more than 1.5 times the baseline value, receipt of renal replacement therapy (RRT) or death

Fig. 7

Kaplan–Meier curves for the recovery from acute kidney injury. a, b Non-recovery from acute kidney injury in four groups in terms of proximal renal venous flow (PRVF) pattern and intrarenal venous flow pattern (IRVF). P value: compared to discontinuous monophasic pattern. c Renal prognosis in different groups in terms of PRVF. P value: compared to 5-day non-improvement group. d Duration time of the discontinuous monophasic pattern of PRVF. P value: compared to 5-day monophasic group. Nonrecovery from AKI was defined as the last available creatinine during the first 28 days of hospitalization remained more than 1.5 times the baseline value, receipt of renal replacement therapy (RRT) or death