An appraisal of respiratory system compliance in mechanically ventilated covid-19 patients

Background: Heterogeneous respiratory system static compliance (C_RS) values and levels of hypoxemia in patients with novel coronavirus disease (COVID-19) requiring mechanical ventilation have been reported in previous small-case series or studies conducted at a national level. Methods: We designed a retrospective observational cohort study with rapid data gathering from the international COVID-19 Critical Care Consortium study to comprehensively describe C_RS—calculated as: tidal volume/[airway plateau pressure-positive end-expiratory pressure (PEEP)]—and its association with ventilatory management and outcomes of COVID-19 patients on mechanical ventilation (MV), admitted to intensive care units (ICU) worldwide. Results: We studied 745 patients from 22 countries, who required admission to the ICU and MV from January 14 to December 31, 2020, and presented at least one value of C_RS within the first seven days of MV. Median (IQR) age was 62 (52–71), patients were predominantly males (68%) and from Europe/North and South America (88%). C_RS, within 48 h from endotracheal intubation, was available in 649 patients and was neither associated with the duration from onset of symptoms to commencement of MV (p = 0.417) nor with PaO₂/FiO₂ (p = 0.100). Females presented lower C_RS than males (95% CI of C_RS difference between females-males: − 11.8 to − 7.4 mL/cmH₂O p < 0.001), and although females presented higher body mass index (BMI), association of BMI with C_RS was marginal (p = 0.139). Ventilatory management varied across C_RS range, resulting in a significant association between C_RS and driving pressure (estimated decrease − 0.31 cmH₂O/L per mL/cmH₂0 of C_RS, 95% CI − 0.48 to − 0.14, p < 0.001). Overall, 28-day ICU mortality, accounting for the competing risk of being discharged within the period, was 35.6% (SE 1.7). Cox proportional hazard analysis demonstrated that C_RS (+ 10 mL/cm H₂O) was only associated with being discharge from the ICU within 28 days (HR 1.14, 95% CI 1.02–1.28, p = 0.018). Conclusions: This multicentre report provides a comprehensive account of C_RS in COVID-19 patients on MV. C_RS measured within 48 h from commencement of MV has marginal predictive value for 28-day mortality, but was associated with being discharged from ICU within the same period. Trial documentation: Available at https://www.covid-critical.com/study. Trial registration: ACTRN12620000421932.