Acute respiratory distress induced by SARS-CoV-2 is a critical clinical condition associated with COVID-19 infection [26, 27]. In a multisystem disease such as COVID-19, a multidisciplinary approach is recommendable [3]; to minimize the high mortality rate potentially associated with COVID-19 pandemics, and to correctly manage this critical condition, adequate hospital resources, structured triage and appropriate clinical training are required. [3]. Clinical evidences led us to consider that, even if the classic criteria defining the ARDS were present in COVID-19 patients [28], atypical aspects were also evident, especially the lack of a reduced lung compliance with the consequent tendency to hypercapnia [29]. The lack of “baby-lung” pattern [30] and the ARDS-like pattern with low lung elastance [17, 19, 31], induced us to evaluate a more specific treatment [15].
According to ARDSnet PEEP table [17, 21], we preferred to ventilate patients with PEEP adapted to patients’ own BMI, carefully tailored to lungs physiology [28, 32]. This approach was consistent with Gattinoni et al [33] and Bendjelid et al [8], who both suggested the presence of two different ICU patient populations in COVID-19 pneumonia. The first population presents a high lung compliance due to a probable alveolitis, with a shunt effect due to loss of local hypoxic vasoconstriction; this population represented the great majority of our patients. The second population presents a low lung compliance and a pattern of “baby-lung” compatible with “classic ARDS” (only 2 patients in our cohort). Following the abovementioned indication, our mechanically ventilated patients were treated with a “low-PEEP approach”, representing thus a different strategy compared to the available literature [34]. More recently, Tsolaki et al [15] Barthélémy et al [16] and Mauri et al [13] suggested a low-PEEP strategy in the management of these “ARDS-like” lungs, on the basis of critically ill patients lung physiology. Agreeing with these evidences, after intubation we found patients easy to ventilate, with a compliance on average above 50 mL/cmH2O higher than in “classic ARDS pattern” [33]. In comparison with other groups [24, 32, 35] our strategy led to less complications (like ICU paralysis, delayed awakening, agitation, etc.), an easier and faster extubation, quickly decreasing deep sedation as inflammation began to diminish, with no need for frequent tracheotomies. Higher PEEP could cause overdistension, resulting in an increased driving pressure, with a subsequent increased risk of lung damage [36–38]; moreover, PEEP levels greater than 10 cmH2O can induce the reduction of venous return, with consequent worsening of the circulation status, as well as local biotrauma and a worsening of alveolar damage [16, 37, 38]. In comparison to Poston JT et al [34], and in agreement with Mauri T et al [13, 15] we applied lower PEEP levels; this approach resulted beneficial, with ventilator data such as P/F ratio showed a rapid improvement already in the first 3 days after OTI. Therefore, the physiology of these ARDS-like lungs, the so-called ARDS L-type [7, 14, 18, 19], appeared to respond appropriately to low PEEP values tailored to patients’ BMI.
Into the Shah et al’s [39] case series, the daily lower limbs ultrasound in COVID-19 ICU patients identified a high prevalence rate of DVTs and PEs, even in patients undergoing prophylactic anticoagulation. In addition, many patients had a marked increase in D-dimers level, possibly linked to VTE in other anatomical districts potentially secondary to PE. In this context, an intermediate anticoagulation seems a reasonable approach, also consequently to recent evidence suggesting the role of endothelial inflammation as a cause of microthrombosis [39, 40]. However, other groups showed an increase in spontaneous bleeding in COVID-19 patients, especially in the retroperitoneal space [35]. In our series, 6 patient presented a major bleeding event; this data was in agreement with the literature [39], bringing forward the hypothesis that an intermediate [9] anticoagulation may counterbalance a phenomenon of prothrombotic diathesis without a relevant increase in hemorrhagic complications rate.
Our COVID-19 ICU patients management resulted in a reduction of the mortality rate (31.6%) when compared to other groups, which reported a 50% and a 61.5% of death rate [41]. We supposed that a relatively low-pressure ventilation could prevent the transition from an initial alveolitis to an iatrogenic ARDS, in which the ongoing inflammation is worsened, rather than treated, by high levels of PEEP, through a Ventilation-Induced-Lung Injury (VILI) mechanism. A median ICU LOS was reported to be equivalent to Bhatraju et al [41], even including patients who died in ICU. This data suggests that a low PEEP strategy with a protective MV approach can improve COVID-19 patients’ in-hospital management, morbidity and mortality, although further studies are necessary to confirm this interesting hypothesis.
Our project was burdened by several limitations. Firstly, this study compared low PEEP in consecutive critically ill COVID-19 patients, and it was not possible to compare the data to a control group; all patients were treated according to emerging information regarding pathophysiological data about the disease [7, 8, 19] and for this reason this strategy was implemented in all critically ill patients admitted to ICU. Secondly, it was a monocentric observational retrospective study, with a relatively small series of patients. However, comparison with current literature was performed; even if patient populations differed, results can be assumed to be consistent, as the cohorts are comparable in terms of disease severity and biochemical markers. Moreover, the low PEEP-strategy was maintained in our Center during the two past waves, allowing us to obtain reproducible results.