Diagnosis and Management of Acute Respiratory Distress Syndrome in a Time of COVID-19

Abstract

Acute respiratory distress syndrome (ARDS) remains a serious illness with significant morbidity and mortality, characterized by hypoxemic respiratory failure most commonly due to pneumonia, sepsis, and aspiration. Early and accurate diagnosis of ARDS depends upon clinical suspicion and chest imaging. Coronavirus disease 2019 (COVID-19) is an important novel cause of ARDS with a distinct time course, imaging and laboratory features from the time of SARS-CoV-2 infection to hypoxemic respiratory failure, which may allow diagnosis and management prior to or at earlier stages of ARDS. Treatment of ARDS remains largely supportive, and consists of incremental respiratory support (high flow nasal oxygen, non-invasive respiratory support, and invasive mechanical ventilation), and avoidance of iatrogenic complications, all of which improve clinical outcomes. COVID-19-associated ARDS is largely similar to other causes of ARDS with respect to pathology and respiratory physiology, and as such, COVID-19 patients with hypoxemic respiratory failure should typically be managed as other patients with ARDS. Non-invasive respiratory support may be beneficial in avoiding intubation in COVID-19 respiratory failure including mild ARDS, especially under conditions of resource constraints or to avoid overwhelming critical care resources. Compared to other causes of ARDS, medical therapies may improve outcomes in COVID-19-associated ARDS, such as dexamethasone and remdesivir. Future improved clinical outcomes in ARDS of all causes depends upon individual patient physiological and biological endotyping in order to improve accuracy and timeliness of diagnosis as well as optimal targeting of future therapies in the right patient at the right time in their disease.

Keywords: COVID-19; SARS-CoV-2; acute respiratory distress syndrome (ARDS); dexamethasone; high flow nasal oxygen; mechanical ventilation; non-invasive ventilation.

Figure 1

Algorithm for hospitalized patients at risk for acute respiratory distress syndrome (ARDS) and coronavirus disease 2019 (COVID-19). In contrast, to COVID-19, there are no specific lab abnormalities which adequately assess severity or predict prognosis in other causes of ARDS. Abbreviations: PaO2, partial pressure of oxygen in arterial blood; FiO2, inspired oxygen fraction; RR, respiratory rate; CRP, C-reactive protein; LDH, lactate dehydrogenase; PEEP, positive end-expiratory pressure; CPAP, continuous positive airway pressure.

Figure 2

Algorithm for respiratory management of patients with hypoxemic respiratory failure. Patients with hypoxemia despite supplemental O₂, including those who meet criteria for mild ARDS, can potentially be managed with non-invasive respiratory support, including HFNO and NIPPV, possibly in combination with self-proning. Sequential escalation of non-invasive respiratory support modalities should be considered unless clinical-physiologic targets are met, depending on local critical care expertise and resources. Patients with moderate–severe ARDS require invasive mechanical ventilation with monitoring and adjustment of ventilatory parameters to minimize ventilator-induced lung injury (VILI), and may benefit from additional measures to improve oxygenation such as prone positioning, recruitment manoeuvres, and potentially veno-venous extra-corporeal membrane oxygenation (VV-ECMO). Notes: a. Non-invasive respiratory support with HFNO/CPAP/NIPPV requires careful monitoring for lack of improvement or persistent respiratory distress, and consideration of intubation/mechanical ventilation. b. All non-invasive and invasive respiratory support modalities are high-risk aerosol-generating medical procedures which should be carried out by experts in airway management, with appropriate precautions (e.g., minimal staff in room, N95, negative pressure room). c. Tidal volume is referenced to predicted body weight. d. Recruitment manoeuvres requires sustained inflation, e.g., inspiratory hold at 35–40 cm H₂O for set time (e.g., 40 s). Stepwise recruitment (with incremental levels of PEEP) is not recommended. e. ROX index = SpO2/FiO2/Respiratory Rate. f. Plateau pressure = airway pressure after 0.5 s pause at end-inspiration. g. Driving pressure = plateau pressure—PEEP. h. Transpulmonary pressure = airway pressure—pleural pressure (under zero flow conditions). i. Static respiratory compliance = tidal volume/(plateau pressure—PEEP). Abbreviations: NP, nasal prongs; FM, facemask; HFNO, high-flow nasal oxygen; CPAP, continuous positive airway pressure; NIPPV, non-invasive positive pressure ventilation; RR, respiratory rate; VT, tidal volume; PEEP, positive end-expiratory pressure; ECMO, extra-corporeal membrane oxygenation. * These interventions, while increasingly being used globally, especially during the COVID-19 pandemic, are not yet supported by robust evidence in patients with ARDS.