Effects of Positive End-Expiratory Pressure in "High Compliance" Severe Acute Respiratory Syndrome Coronavirus 2 Acute Respiratory Distress Syndrome.

OBJECTIVES: Clinical observation suggests that early acute respiratory distress syndrome induced by the severe acute respiratory syndrome coronavirus 2 may be "atypical" due to a discrepancy between a relatively unaffected static respiratory system compliance and a significant hypoxemia. This would imply an "atypical" response to the positive end-expiratory pressure. DESIGN: Single-center, unblinded, crossover study. SETTING: ICU of Bari Policlinico Academic Hospital (Italy), dedicated to care patients with confirmed diagnosis of novel coronavirus disease 2019. PATIENTS: Eight patients with early severe acute respiratory syndrome coronavirus 2 acute respiratory distress syndrome and static respiratory compliance higher than or equal to 50 mL/cm H2O. INTERVENTIONS: We compared a "lower" and a "higher" positive end-expiratory pressure approach, respectively, according to the intervention arms of the acute respiratory distress syndrome network and the positive end-expiratory pressure setting in adults with acute respiratory distress syndrome studies. MEASUREMENTS AND MAIN RESULTS: Patients were ventilated with the acute respiratory distress syndrome network and, subsequently, with the ExPress protocol. After 1 hour of ventilation, for each protocol, we recorded arterial blood gas, respiratory mechanics, alveolar recruitment, and hemodynamic variables. Comparisons were performed with analysis of variance for repeated measures or Friedman test as appropriate. Positive end-expiratory pressure was increased from 9 ± 3.5 to 17.7 ± 1.7 cm H2O (p < 0.01). Alveolar recruitment was 450 ± 111 mL. Static respiratory system compliance decreased from 58.3 ± 7.6 mL/cm H2O to 47.4 ± 14.5 mL/cm H2O (p = 0.018) and the "stress index" increased from 0.97 ± 0.03 to 1.22 ± 0.07 (p < 0.001). The PaO2/FIO2 ratio increased from 131 ± 22 to 207 ± 41 (p < 0.001), and the PaCO2 increased from 45.9 ± 12.7 to 49.8 ± 13.2 mm Hg (p < 0.001). The cardiac index went from 3.6 ± 0.4 to 2.9 ± 0.6 L/min/m (p = 0.01). CONCLUSIONS: Our data suggest that the "higher" positive end-expiratory pressure approach in patients with severe acute respiratory syndrome coronavirus 2 acute respiratory distress syndrome and high compliance improves oxygenation and lung aeration but may result in alveolar hyperinflation and hemodynamic alterations.

A Pilot Study on Electrical Impedance Tomography During CPAP Trial in Patients With Severe Acute Respiratory Syndrome Coronavirus 2 Pneumonia: The Bright Side of Non-invasive Ventilation.

Background: Different severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pneumonia phenotypes were described that match with different lung compliance and level of oxygenation, thus requiring a personalized ventilator setting. The burden of so many patients and the lack of intensive care unit (ICU) beds often force physicians to choose non-invasive ventilation (NIV) as the first approach, even if no consent has still been reached to discriminate whether it is safer to choose straightforward intubation, paralysis, and protective ventilation. Under such conditions, electrical impedance tomography (EIT), a non-invasive bedside tool to monitor lung ventilation and perfusion defects, could be useful to assess the response of patients to NIV and choose rapidly the right ventilatory strategy. Objective: The rationale behind this study is that derecruitment is a more efficient measure of positive end expiratory pressure (PEEP)-dependency of patients than recruitment. We hypothesized that patients who derecruit significantly when PEEP is reduced are the ones that do not need early intubation while small end-expiratory lung volume (ΔEELV) variations after a single step of PEEP de-escalation could be predictive of NIV failure. Materials and Methods: Consecutive patients admitted to ICU with confirmed SARS-CoV-2 pneumonia ventilated in NIV were enrolled. Exclusion criteria were former intubation or NIV lasting > 72 h. A trial of continuos positive airway pressure (CPAP) 12 was applied in every patient for at least 15 min, followed by the second period of CPAP 6, either in the supine or prone position. Besides standard monitoring, ventilation of patients was assessed by EIT, and end-expiratory lung impedance (ΔEELI) (%) was calculated as the difference in EELI between CPAP12 and CPAP6. Tidal volume (Vt), Ve, respiratory rate (RR), and FiO2 were recorded, and ABGs were measured. Data were analyzed offline using the dedicated software. The decision to intubate or continue NIV was in charge of treating physicians, independently from study results. Outcomes of patients in terms of intubation rate and ICU mortality were recorded. Results: We enrolled 10 male patients, with a mean age of 67 years. Six patients (60%) were successfully treated by NIV until ICU discharge (Group S), and four patients failed NIV and were intubated and switched to MV (Group F). All these patients died in ICU. During the supine CPAP decremental trial, all patients experienced an increase in RR and Ve. ΔEELI was < 40% in Group F and > 50% in Group S. In the prone trial, ΔEELI was > 50% in all patients, while RR decreased in Group S and remained unchanged in Group F. Conclusion: ΔEELI < 40% after a single PEEP de-escalation step in supine position seems to be a good predictor of poor recruitment and CPAP failure.