888: COMPARISON OF THE PROGNOSTIC VALUE OF PULMONARY DEAD SPACE PROXIES IN COVID-19 ARDS OUTCOMES

Abstract

Introduction: Mortality and morbidity associated with COVID-19 acute respiratory distress syndrome (ARDS) has been associated with pulmonary vasculopathy, which has been hypothesized to increase pulmonary dead space (VD/VT). However, VD/VT is rarely measured at the bedside. As a result, multiple proxy estimates have been developed. Our hypothesis was proxy estimates for VD/VT would have differing utilities in prognostication of COVID-19 ARDS. Methods: We conducted a retrospective cohort study of patients admitted to an intensive care unit with SARS-CoV-2 ARDS who required invasive mechanical ventilation. Ventilation parameters were collected 2-8 hours after intubation. The VD/Vt proxies examined were 1) ventilatory ratio (VR), 2) estimation of VD/VT using the Harris-Benedict equation for energy expenditure (VD/VT-HB), 3) direct estimation of VD/VT using Beitler et. al.’s formula (VD/VT-Dir), and 4) corrected minute ventilation (VECorr). For each proxy, subjects were dichotomized using the median value. Comparisons were performed using the Wilcoxon rank-sum test with ⍺=0.05. Results: For 139 subjects, mean VR was 2.08 (SD±0.80), mean VD/VT-HB was 0.614 (±0.15), mean VD/VT-Dir was 0.657 (±0.08), and mean VECorr was 12.2 (±4.6) L/min. All four proxies had strong inter-measure correlation (Pearson’s r 0.748-0.881, p< 0.001 for all comparisons). No proxy was predictive of 30-day hospital mortality. High VR and VECorr were associated with increased morbidity using a composite endpoint of death or organ failure (defined as requiring renal dialysis or extracorporeal membrane oxygenation) with both having an odds ratio of 2.20 (95% CI: 1.12-4.33, p=0.022), while VD/VT-HB (p=0.552) and VD/VT-Dir (p=0.554) were not significantly associated. Of all proxies, only VR was significantly associated with increased sequential organ failure assessment (SOFA) score at 10±4 days post-intubation (6.2 vs. 4.8, p=0.024) and more ventilator-free days within the 30 days after intubation (3.2 vs. 1.8, p=0.029). Conclusions: Ventilatory ratio and corrected minute volume appear to have stronger associations with morbidity in COVID-19 ARDS compared to other VD/VT estimates. Ventilatory ratio is also associated with ventilator-free days and delayed SOFA score.