Evolution of respiratory system compliance and potential for lung recruitment in COVID-19–induced acute respiratory distress syndrome

Background:Coronavirus disease 2019(COVID-19)has been frequently complicated by severe acute respiratory distress syndrome(ARDS)with prolonged invasive ventilation.While respiratory system compliance and lung recruitability have been described within the first days after ICU admission,data about their longitudinal changes are still limited.Therefore,we conducted this study to assess the evolution of respiratory system compliance and lung recruitability in patients with COVID-19–related ARDS.Method:We conducted a prospective single-center study in patients admitted for COVID-19–related ARDS during the first wave of the pandemic,from March 16,2020 to April 10,2020.Respiratory system compliance was calculated daily at clinical positive end-expiratory pressure(PEEP)during passive breathing.The potential for lung recruitment was assessed by measuring the volume derecruited between PEEP 15 cmH2 O and 5 cmH2 O,and using the calculation of the recruitment-to-inflation ratio(R/I ratio).Recruitable lung was considered when the R/I ratio was at least 0.5.The primary outcome was the evolution of respiratory mechanics over time.The secondary outcome was the evolution of lung recruitability over time.Results:Thirty-two patients were included in this study.The respiratory mechanics were assessed 222 times(7±5 times per patient).Respiratory system compliance at clinical PEEP was 29.1 mL/cmH2 O(interquartile range[IQR]:24.1–33.9 mL/cmH2 O)and decreased significantly over time(P<0.0001).Lung recruitability was assessed in 22 out of the 32 patients(60 assessments).The median volume derecruited between PEEP 15 cmH2 O and 5 cmH2 O was 246.8 mL(IQR:180.8–352.2 mL)and the median R/I ratio was 0.56(IQR:0.39–0.73).Neither changed significantly over time.The proportion of patients with recruitable lung was 50.0%(6/12)within the first 3 days after intubation,69.2%(9/13)between day 4 and day 7,and 66.7%(8/12)after day 7(P=0.7934).Conclusions:In our cohort,respiratory system compliance was low and decreased over time.The potential for lung recruitment was high and persisted despite prolonged mechanical ventilation,suggesting that maintaining high PEEP levels in the later course of COVID-19 could be adequate.

Influence of positive end-expiratory pressure upregulation on the right ventricle in critical patients with acute respiratory distress syndrome:an observational cohort study

Background This study aimed to investigate the influence of positive end-expiratory pressure(PEEP)on the right ventricle(RV)of mechanical ventilation-assisted patients through echocardiography.Methods Seventy-six patients assisted with mechanical ventilation were enrolled in this study.Positive end-expiratory pressure was upregulated by 4 cm H_(2)O to treat acute respiratory distress syndrome,wherein echocardiography was performed before and after this process.Hemodynamic data were also recorded.All variables were compared before and after PEEP upregulation.The effect of PEEP was also evaluated in patients with and without decreased static lung compliance(SLC).Results Positive end-expiratory pressure upregulation significantly affected the RV function.Remarkable differences were observed in the following:Tei index(P=0.027),pulmonary artery pressure(P=0.039),tricuspid annular plane systolic excursion(P=0.014),early wave/atrial wave(P=0.002),diaphragm excursion(P<0.001),inferior vena cava collapsing index(P<0.001),and SLC(P<0.001).There were no significant changes in heart rate,respiratory rate,central venous pressure,mean arterial pressure,and base excess(P>0.05).Furthermore,the cardiac output of the RV was not significantly affected.In patients with decreased SLC(n=41),there were more significant changes in diaphragm excursion(P<0.001),inferior vena cava collapse index(P=0.025),pulmonary artery pressure(P<0.001),and tricuspid annular plane systolic excursion(P=0.007)than in those without decreased SLC(n=35).Conclusion Positive end-expiratory pressure upregulation significantly affected the RV function of critically ill patients with acute respiratory distress syndrome,especially in those with decreased SLC.

Physiological Correlation of Airway Pressure and Transpulmonary Pressure Stress Index on Respiratory Mechanics in Acute Respiratory Failure

Background： Stress index at post-recruitment maneuvers could be a method of positive end-expiratory pressure （PEEP） titration in acute respiratory distress syndrome （ARDS） patients. However, airway pressure （P_aw） stress index may not reflect lung mechanics in the patients with high chest wall elastance. This study was to evaluate the P stress index on lung mechanics and the correlation between P stress index and transpulmonary pressure （P_L） stress index in acute respiratory failure （ARF） patients. Methods： Twenty-four ARF patients with mechanical ventilation （MV） were consecutively recruited from July 2011 to April 2013 in Zhongda Hospital, Nanjing, China and Ospedale S. Giovanni Battista-Molinette Hospital, Turin, Italy. All patients underwent MV with volume control （tidal volume 6 ml/kg） for 20 rain. PEEP was set according to the ARDSnet study protocol. The patients were divided into two groups according to the chest wall elastance/respiratory system elastance ratio. The high elastance group （H group, n = 14） had a ratio _〉30%, and the low elastance group （L group, n = 10） had a ratio 〈30%. Respiratory elastance, gas-exchange, P stress index, and Pt stress index were measured. Student＇s t-test, regression analysis, and Bland-Altman analysis were used for statistical analysis. Results： Pneumonia was the major cause of respiratory failure （71.0%）. Compared with the L group, PEEP was lower in the H group （5.7 ± 1.7 cmH,O vs. 9.0 ± 2.3 cmH2O, P 〈 0.01 ）. Compared with the H group, lung elastance was higher （20.0 ± 7.8 cmH20/L vs. 11.6 ± 3.6 cmH,O/L, P 〈 0.01）, and stress was higher in the L group （7.0 ±1.9 vs. 4.9 ± 1.9, P = 0.02）. A linear relationship was observed between the P stress index and the P stress index in H group （x2 = 0.56, P 〈 0.01 ） and L group （x2 = 0.85, P 〈 0.01）. Conclusion： In the ARF patients with MV, P,w stress index can substitute for PL to guide ventilator settings.