SARS-CoV-2-induced Acute Respiratory Distress Syndrome: Pulmonary Mechanics and Gas-Exchange Abnormalities

Abstract

In January 2020, the first cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection were reported in Europe. Multiple outbreaks have since then led to a global pandemic, as well as to massive medical, economic, and social repercussions. SARS-CoV-2 pneumonia can develop into acute respiratory distress syndrome (ARDS) when mechanical ventilation (MV) is needed (3, 4). ARDS produces abnormalities in gas exchange with a variable degree of shunt (5), high dead space ventilation (dead space volume [Vd]/tidal volume [Vt] ratio) (6), diminished pulmonary compliance (7), and alterations to the pulmonary circulation (8). The cornerstone of ARDS management is to provide adequate gas exchange without further lung injury as a result of MV. To date, information regarding the characteristics of SARS-CoV-2-induced ARDS is not completely known. However, this information is crucial to better apply MV and facilitate organ support strategies. We therefore present the characteristics of gas exchange, pulmonary mechanics, and ventilatory management of 50 patients with laboratory-confirmed SARS-CoV-2 infection, who developed ARDS and underwent invasive MV (IMV). Methods: Descriptive analysis included 50 consecutive patients with laboratory-confirmed SARS-CoV-2 infection who developed ARDS (9) and underwent IMV. These patients were admitted to the SARS-CoV-2-dedicated intensive care units (ICUs) at Hospital Clinic of Barcelona, Spain, between March 7 and March 25, 2020. Upon ICU admission, epidemiological characteristics, the severity of SARS-CoV-2 infection with the Acute Physiology and Chronic Health Evaluation II score, prognostic biomarkers of SARS-CoV-2 infection (described in Reference 4), time from hospital to ICU admission, time from ICU admission to intubation, oxygen therapy or noninvasive ventilation (NIV) use, and microbiology were investigated. On the day that criteria for ARDS diagnosis were met (9) and IMV was needed, the following assessments were performed: impairment in oxygenation was analyzed with the partial pressure of oxygen (PaO2)/fraction of inspired oxygen (FiO2) ratio, and abnormalities of CO2 metabolism were studied with the ventilatory ratio (VR), a surrogate parameter of Vd/Vt. In addition, adjunctive therapies and MV parameters related with ventilation-induced lung injury (VILI) described elsewhere (11-15) were investigated. Correlations of SARS-CoV-2 prognostic biomarkers (4), pulmonary mechanics, and gas-exchange data were performed. Twenty-eight-day and hospital mortality, ventilator- and ICU-free days at Day 28, hospital and ICU lengths of stay, and need for tracheostomy were also evaluated (16). Finally, a subanalysis assessing differences before and after prone positioning was performed. For additional detail on the method, see the online supplement. Results: By March 25th, 2020, 50 patients with laboratory-confirmed SARS-CoV-2 infection and ARDS had been admitted to our hospital. Table 1 shows the demographic and clinical characteristics of these patients. The median (interquartile range [IQR]) age was 66 (57-74) years. Thirty-six patients (72%) were men. Upon ARDS diagnosis, 44% of patients were initially classified as having moderate ARDS, whereas 24% were classified as having mild ARDS and 32% were classified as having severe ARDS. The outcomes of these patients are shown in Table 1. ICU and hospital lengths of stay were prolonged, and tracheostomy was performed in 30 (60%) patients. Hospital mortality was 34%.