Table 1 The diagnostic criterion for severe and critically ill COVID-19

Severe COVID-19 is defined as (no matter how long the condition lasts, at least one of the following conditions):

 • Shortness of breath and respiratory rate ≥ 30 breaths/minute

 • Clinical symptoms progressively worsen, and lung radiographic infiltrates by imaging (eg, chest x-ray, CT scan.) show > 50% lung infiltrates within 24–48 h

 • PaO₂) / (FiO₂) ≤ 300 mmHg (1 mmHg = 0.133 kPa)

 • Oxygen saturation ≤ 93% in resting state

Critically ill COVID-19 is defined as (at least one of the following conditions):

 • Respiratory failure (defined as the need to receive at least one of the following treatments according to local medical resources/conditions: endotracheal intubation and mechanical ventilation, high-flow nasal catheter oxygen supply (heating, humidification, enhanced nasal catheter oxygen supply, flow rate > 20 L/minute, oxygen supply ratio ≥ 0.5), positive pressure ventilation, ECMO, or clinical diagnosis of respiratory failure (defined as none of the above treatments cannot provide due to limited medical resources)

 • Shock (defined as systolic blood pressure < 90 mm Hg, diastolic blood pressure < 60 mm Hg, or the need for vasopressors)

 • Multiple organ dysfunction/failure