ABSTRACT
INTRODUCTION: Ventilatory ratio (VR) is a simple bedside index of carbon dioxide removal. VR correlates well with physiologic dead space fraction (VD/VT) and clinical outcomes in patients with acute respiratory distress syndrome (ARDS). We hypothesized that high VR would identify COVID-19 ARDS patients with higher risk for death and organ failure. METHOD(S): We conducted a retrospective cohort study of patients admitted to a single hospital in New York, NY, USA from March-July 2020 who had PCR-confirmed SARS-CoV-2 infection, met the Berlin criteria for ARDS, and required tracheostomy for prolonged invasive mechanical ventilation (MV). MV parameters were collected 2-8 hours after intubation. Based on prior studies, a VR>2 was considered to be abnormally elevated. Comparisons were performed using the Wilcoxon rank-sum test or z-test for difference in proportions with alpha=0.05. The primary outcome was 30- day mortality and the secondary outcome was a composite endpoint of death or organ failure defined as requiring renal replacement or extracorporeal membrane oxygenation (ECMO) during the hospitalization. RESULT(S): Of 139 subjects enrolled, 67 (48.2%) had a VR>2. Low and high VR groups had similar baseline characteristics, including age (mean 58 years, SD +/-15.2), body mass index (30.1+/-6.69 kg/m2), simplified acute physiology score II (35.4+/-12.4), sequential organ failure assessment (SOFA) score (5.7+/-2.5), and a 19-point review of systemic disease history. High VR was not significantly associated with mortality (OR 0.92, p=0.827). However, high VR was associated with increased risk for the composite endpoint (OR 1.96, p=0.049) and independently identified patients with a higher risk of organ failure (OR 2.03, p=0.047). High VR was also associated with longer hospital length-of-stay for subjects who survived to discharge (52 vs. 43, p=0.035), more MV-free days within the 30 days after intubation (3.2 vs. 1.8, p=0.029), and higher SOFA score at 10+/-4 days post-intubation (6.2 vs. 4.8, p=0.024). CONCLUSION(S): Ventilatory ratio identifies COVID-ARDS ventilated patients with increased risk for organ failure requiring advanced intervention, as well as patients who may require prolonged mechanical ventilation and hospitalization.
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. METHOD(S): We conducted a retrospective cohort study of patients admitted to an intensive care unit with SARSCoV- 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/VTDir), 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 alpha=0.05. RESULT(S): 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 ventilatorfree days within the 30 days after intubation (3.2 vs. 1.8, p=0.029). CONCLUSION(S): 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.
ABSTRACT
INTRODUCTION: Ventilatory ratio (VR) is a bedside index of impaired ventilation that can be used as a surrogate marker for pulmonary dead space fraction (VD/VT). Vasculopathy is hypothesized to increase VD/VT in patients with acute respiratory distress syndrome (ARDS) due to COVID-19. The purpose of this study was to investigate associations between VR and markers of inflammation in critically ill COVID-ARDS patients. METHOD(S): We conducted a retrospective study of patients admitted to an intensive care unit due to SARS-CoV-2 infection. All subjects required invasive mechanical ventilation and met the Berlin criteria for ARDS. Clinical lab values were collected at two timepoints: 2-8 hours after intubation (T1) and 2-24 hours before tracheostomy (T2). VR was split into high (VR>2) and low (VR< 2) groups. Comparisons were performed using student's t, Mann-Whitney, and z tests for difference in proportions with alpha=0.05. RESULT(S): Of the 139 subjects enrolled at T1, 67 (48%) had high VR (>2), with an overall mean VR of 2.08. High VR was significantly associated with leukocyte count (WBC) (13.3 vs. 10.6 x10