There were differences in the duration of mechanical ventilation among the two groups (6 vs. 9 days, P = 0.024) [Table 1], and the total RRT time was significantly different between the two groups (P < 0.001). However, the ICU retention time and hospitalization time were not different between the two groups (14 vs. 16 days, P = 0.236; 26 vs. 28 days, P = 0.762, respectively). Cr and blood urea nitrogen (BUN) levels were different at the start of RRT between the two groups. There were no differences between the two groups in mortality at discharge. However, renal function recovery between the two groups showed significant differences.
Patients were divided into three groups according to the recovery of renal function, and we analyzed the factors that may affect renal function recovery. Our study found that there was no significant differences in Cr, BUN, MAP, or DAP at the initiation of RRT (P > 0.05). However, the early or delayed strategy of RRT was different between different groups, and the level of CVP, DPP, and fluid balance was different between those groups. At the same time, we did not find any difference in the venous-to-arterial carbon dioxide (Pv-aCO2) or ScvO2 of different groups, which means that the cardiac function of those patients was not a factor affecting renal function in any of the three groups [Table 2].
When we evaluated the CVP levels in different renal function recovery conditions, we found that in those patients who received early initiation RRT, CVP decreased significantly and correlated with rapid renal function recovery at discharge (P < 0.05) [Figure 2].
We conducted an ordinal polytomous logistic regression analysis of the factors that may affect the recovery of renal function, and we found that early strategy of RRT and a decline of CVP can promote the recovery of renal function (P = 0.031, P = 0.001; respectively) [Table 3].
This study indicated that in patients with septic AKI, early initiation RRT for fluid management improved the recovery of kidney function. In addition, the recovery of renal function was correlated with the decrease of CVP level, this effect was more prominent in patients who received early initiation RRT.
The timing of initiation of RRT depends on numerous factors and is, therefore, a complex process. Some previous studies suggested that a survival advantage is associated with early RRT.[25,26] Recently, two randomized, controlled studies explored this question, but they came to the opposite conclusion.[12,27] Our trial found no significant difference in mortality at 28 days between the early initiation renal replacement group and the delayed strategy group; this result is consistent with previous reports. Although there was no difference in mortality between the two groups, we found some notable differences in clinical outcomes that merit further discussion. First, we found that delayed initiation of RRT was generally associated with a longer duration of RRT support and mechanical ventilation time. Second, we found that delayed initiation of RRT was associated with inferior renal recovery and a higher rate of dialysis dependence at hospital discharge.
The cause of kidney injury is not only the toxic effect of Cr and BUN but also the damaging effect of a high level of CVP and fluid overload on the kidney with a long duration. The pathophysiology of congestive renal failure includes reduced transglomerular pressure, elevated renal interstitial pressure, and enhanced proinflammatory pathways. Earlier initiation of dialysis in AKI might improve the control of acid-base status and the removal of toxins; these changes can reduce the burden on the kidneys, thereby preventing further deterioration of renal function. The effect of fluid management and CVP on the recovery of renal function in RRT treatment is still unclear.
In this study, we compared patients with different levels of recovery of renal function and found that the recovery of renal function was correlated with the initiation of RRT, CVP levels, liquid equilibrium state, and DPP levels. Further regression analysis of these factors showed that the main factors affecting the recovery of renal function were the initiation of RRT and the levels of CVP. The liquid equilibrium state was statistically insignificant in the regression analysis; a possible explanation for this phenomenon is that the liquid overload state in patients is not positively correlated with CVP and that the backward resistance of the systemic circulation may be more important than the overall liquid balance state in patients with AKI.
Previous studies have found that the baseline CVP of patients with AKI is higher than that of patients without AKI. Damman et al confirmed that CVP affected kidney function not only in patients with heart failure but also in patients with normal heart function. Our study found that the CVP levels of patients with rapid renal function recovery were lower than those whose kidney function recovered more gradually; this phenomenon was more obvious in patients who received early-initiation RRT. More importantly, when different renal function recovery situations were compared, there were no differences in other factors such as the Pv-aCO2 and ScvO2, suggesting that there is no significant difference in heart function between patients with different kidney function recovery. These results fully demonstrated that early application of RRT to reduce CVP was crucial for renal function recovery.
Maintaining optimal blood pressure is an important aspect of preventing AKI, especially for vasopressor-dependent patients. MAP is widely used as an index for the optimal blood pressure. However, a recent observational study revealed that lower DAP and higher CVP were associated with septic AKI, while MAP was not. Another observational study reported that decreased MAP was not associated with AKI, suggesting that only DPP and CVP may be associated with septic AKI. Our study confirmed that high CVP and low DPP were important factors affecting renal function recovery. At the same time, it is more likely that different levels of CVP lead to different DPP. Therefore, high CVP is the most important factor affecting renal perfusion pressure.
There were several limitations to this study. First, this was a retrospective study, and the number of patients was small, which was likely to introduce bias. Second, various factors, such as positive end-expiratory pressure was not investigated. Third, the lack of long-term renal function indicators and the speed of renal function recovery may have an impact on long-term renal function and quality of life. Additional studies are required to investigate the effect of different treatment strategies on long-term renal function.
In conclusion, our study confirmes that early initiation RRT for fluid management to reduce CVP levels is conducive to the recovery of renal function in patients with sepsis kidney injury compared with the delayed-initiation RRT strategy.
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