Electrocardiographic Time-Intervals Waveforms as Potential Predictors for Severe Acute Kidney Injury in Critically Ill Patients

Abstract

Background: Acute kidney injury (AKI) is common in critically ill patients admitted to intensive care units (ICU) and is frequently associated with poorer outcomes. Hence, if an indicator is available for predicting severe AKI within the first few hours of admission, management strategies can be put into place to improve outcomes. Materials and methods: This was a prospective, observational study, involving 63 critically ill patients, that aimed to explore the diagnostic accuracy of different Doppler parameters in predicting AKI in critically ill patients from a mixed ICU. Participants were enrolled at ICU admission. All underwent ultrasonographic examinations and hemodynamic assessment. Renal Doppler resistive index (RDRI), venous impedance index (VII), arterial systolic time intervals (a-STI), and venous systolic time intervals (v-STI) were measured within 2 h from ICU admission. Results: Cox proportional hazards models, including a-STI, v-STI, VII, and RDRI as independent variables, returned a-STI as the only putative predictor for the development of AKI or severe AKI. An overall statistically significant difference (p < 0.001) was observed in the Kaplan−Meier plots for cumulative AKI events between patients with a-STI higher or equal than 0.37 and for cumulative severe AKI-3 between patients with a-STI higher or equal than 0.63. As assessed by the area under the receiver operating curves (ROC) curves, a-STI performed best in diagnosing any AKI and/or severe AKI-3. Positive correlations were found between a-STI and the N-terminal brain natriuretic peptide precursor (NT-pro BNP) (ρ = 0.442, p < 0.001), the sequential organ failure assessment (SOFA) score (ρ: 0.361, p = 0.004), and baseline serum creatinine (ρ: 0.529, p < 0.001). Conclusions: Critically ill patients who developed AKI had statistically significant different a-STI (on admission to ICU), v-STI, and VII than those who did not. Moreover, a-STI was associated with the development of AKI at day 5 and provided the best diagnostic accuracy for the diagnosis of any AKI or severe AKI compared with RDRI, VII, and v-STI.

Keywords: acute kidney disease; hypoperfusion; renal Doppler resistive index; renal ultrasonography; splanchnic congestion; venous impedance index.

Figure 1

Panel (A) the arterial trace is shown above the green reference line. Renal Doppler resistive index is calculated as the ratio (S-D)/S, where S and D stand for peak systolic and end-diastolic velocities, respectively; arterial systolic time-intervals indicates the proportion of the cardiac-cycle during which there is an effective arterial perfusion and was calculated in milliseconds on the real-time ECG-trace as (renal pre-Ejection Time/renal Ejection Time). Renal pre-Ejection Time (red area) is calculated from onset of QRS complex to the foot of renal Doppler waveform. Renal ejection time (blue area) is measured from the foot of renal Doppler waveform to the dicrotic-notch of the renal pulse Doppler waveform; the continuous venous trace is shown below the green reference line. The venous impedence index is calculated as the peak maximum flow velocity minus the flow velocity at nadir, divided by peak maximum flow velocity. When venous flow is discontinuous, the index is 1.0, as the flow at nadir is 0. Panel (B) the discontinuous venous trace is shown below the green reference line. Venous systolic time-intervals indicates the proportion of the cardiac cycle measured in milliseconds from a QRS to the next QRS on the ECG-trace (pink line) during which there is no renal venous outlet flow (yellow lines) and is calculated as follows: (cardiac cycle time–venous flow time/cardiac cycle time). When venous flow is continuous, the v-STI is 0, as the venous flow time equals the cardiac cycle time.

Figure 2

Flowchart of studied patients.

Figure 3

Doppler values assessed at ICU admission according to KDIGO stage at day 5. Panel (A) Arterial systolic time intervals (a-STI); Panel (B) renal Doppler resistive index (RDRI); Panel (C) renal venous impedence index (VII); Panel (D) venous time intervals (v-STI); Kidney Disease Improving Global Outcomes score (KIDIGO).

Figure 4

Panel (A): Comparison of the Kaplan-Meier curves for lack of adverse outcomes [any acute kidney injury (AKI)] in patients with a-STI equal or lower than 0.37 by using the log-rank test (p < 0.001). Panel (B): Comparison of the Kaplan-Meier curves for lack of adverse outcomes (AKI-3) in patients with a-STI equal or lower than 0.63 by using the log-rank test (p < 0.001). The number of patients at each time point is shown as a drop on the corresponding line. Patients were censored at day 5.

Figure 5

Receiver operator characteristic (ROC) curves for arterial systolic time intervals (a-STI), renal Doppler resistive index (RDRI), venous systolic time intervals (v-STI), venous impedence index (VII) as putative predictors for any acute kidney injury (AKI) (panel (A)) or severe AKI (panel (B)).