In the present study, we found no association between PEEP levels and WRF. CVP levels are associated with the risk of WRF, especially above 10 mmHg. PEEP may be associated with WRF through its impact on CVP. Inflammation also seems to be a contributor to WRF.
The relationship between PEEP and AKI has been evoked multiple times in the literature [29], [30], [31], [32]. Anyway, few studies investigated the impact of PEEP levels on occurrence or persistence of AKI to date. The COVID-19 pandemic recently emphasized the major importance of adequate ventilator management of ARDS patients. We showed that PEEP has a dramatic impact on global hemodynamics and may reduce oxygen delivery while improving P/F ratio [33].
The contribution of right side pressure, i.e. CVP, to AKI has been well described [21], [22]. A strength of our study is to investigate together PEEP and CVP impact on AKI. The global impact of PEEP on CVP is uncertain [34], [35], [36] and relies on various factors (hypovolemia, compliance, right heart function, etc.). The extent of CVP rise associated with the increase of PEEP varies greatly. High levels of PEEP are not necessarily associated with elevated CVP. Here, we show that PEEP levels did not differ between patient with or without WRF. Consistently with literature [37], we found an increased risk of WRF with high values of CVP (above 10 mmHg). PEEP may contribute to occurrence of WRF through its impact on CVP. Therefore, ventilatory and hemodynamic management of COVID-19 ARDS patients should focus on the evolution of CVP in order to prevent kidney injury.
Interestingly, we found that inflammation was a risk factor of WRF. One study has recently found that high neutrophils count in ICU was associated with severe AKI [18]. Our results support the hypothesis of a role of inflammation in case of AKI in COVID 19.
Thus, management of the inflammatory part of AKI relies on the control of the disease and may respond to immunomodulatory treatments that were recently put under the light with the pandemic.
In the present study, we decided to consider both new AKI and persistent AKI together. This concept of WRF fits well with ICU daily practice. Indeed, a large proportion of AKI occurs before ICU admission [38] .It seems adequate to consider that the same factors contribute to both development and persistence of AKI.
Our study suffers several limitations. First, the retrospective, single center, nature of our study may prevent us generalizing our results. However, our center is expert in hemodynamic monitoring, with a trained and experienced team, implying that the CVP values reported can be considered reliable. More, all the patients were treated homogeneously, with local protocols in accordance with international guidelines [39]. Second, the CVP levels reported were relatively low. This can be explained by the fact that our teams is concerned about maintaining low CVP, in order to limit the repercussions of subsequent right side heart failure. Last, this study was conducted during the first wave of COVID 19, implying that none of these patients received immunomodulatory therapy such as dexamethasone or tocilizumab. In addition, some of these patients did not immediately benefit from enhanced preventive anticoagulation as recommended now [40].
Based on these results, it appears that kidney protection should be an objective of the ventilatory strategy.