Global Cases Reported by WHO
Who Are Categorized as Severe COVID-19 Cases?
When a COVID-19 patient has respiratory dyspnea and the oxygen therapy has failed relief the symptoms, then patient is identified as severe hypoxic respiratory failure. An ineffective oxygen therapy means that the patient is using an oxygen reservoir mask with flow of 10L-15L/min (usually at minimal flow rate to maintain bag inflation with 60%-95% FiO2), but continues to show increasing respiratory rate with hypoxemia. Severe hypoxic respiratory failure often results in intrapulmonary shunt caused by V/Q imbalance (also referred to as ventilation-perfusion mismatch), therefore, different ventilation strategies should be used to adapt to the acuity level of each patient.
Invasive Mechanical Ventilation (IMV)
1. Clinical Consensus
- PaO2/FiO2 rises;
- PaCO2 decreases;
- Respiratory compliance improves.
PEEP Titration: Setting the appropriate PEEP is important to maintain oxygenation of ARDS patients and to avoid lung injuries. PEEP titration is necessary to keep the lung open after recruitment. There are several PEEP titration methods commonly used by clinicians including : ARDSnet FIO2-PEEP table, Low ﬂow P-V curve, Best Oxygenation, Stress index, PEEP Decremental, and Transpulmonary pressure.
2. Solutions for invasive ventilation
Lower Tidal Volume
TVe/IBW Monitoring：Mindray SV Series ventilator can set the default TVe/IBW strategy to its volume control mode as well as monitor it in real time during ventilation, so that clinicians can keep track of the patient's real-time expired tidal volume.
Lung Recruitment Maneuvers
Sustained Inflation (SI)：Mindray’s SV Series ventilators are equipped with lung recruitment tool: sustained inflation , allowing clinicians to choose the suitable tool according to the specific requirement of the patient. It is recommended that you choose the recruitment maneuver that you’re most familiar with.
P-V Tool：Mindray ventilators can provide low-flow P-V Tool and automatically identify the inflection points. Using the low flow P-V curve method can help the doctors to find the optimal PEEP as well as guide on alarm limit settings and reflect the patient’s current lung status.
Esophageal Pressure Monitoring (Pes): Mindray’s ventilators can provide dual-channel auxiliary pressure monitoring, allowing one of the sensor to measure the esophageal pressure. The transpulmonary pressure can be accurately calculated by esophageal pressure monitoring and thus help efficiently guide the optimal PEEP setting. In addition, another auxiliary pressure sensor can be used for measuring other indicators, such as intragastric pressure.
Respiratory Mechanics Measurement
PulmoSight：It is essential to closely monitor the changes of respiratory mechanics during PEEP titration in ARDS patients. The SV Series ventilators monitor patient’s respiratory mechanics and display the data in a graphic way - PulmoSight to help display intuitive real-time feedback.
Non-Invasive Mechanical Ventilation (NIV)
1. Clinical Consensus
For severe cases of COVID-19, when the patient’s PaO2/FiO2 is between 150 mmHg and 200 mmHg, start with non-invasive ventilation. The initial NIV parameters are to be set as the following:
- Inspiratory positive airway pressure (IPAP): 8 cmH2O to 10 cmH2O (1 cmH2O = 0.098 kPa);
- Expiratory positive airway pressure (EPAP) : 5 cmH2O to 8 cmH2O;
- FiO2: 100%.
Observe for 2 hours. During this period, NIV parameters need to be adjusted according to the patient's breathing status, tidal volume (Vt) and SpO2.
- if Vt is < 9ml/kg, RR is <30 times/min and PaO2/FiO2 is stable or improved, then continue NIV treatment;
- if Vt is between 9 ml/kg - 12 ml/kg, PaO2/FiO2 is stable, then use NIV and observe the patient for 6 hours;
- during which if Vt is > 12 ml/kg or PaO2/FiO2 worsens, then immediately stop NIV and change to invasive ventilation (endotracheal intubation).
2. Solutions for NIV
Mindray SV Series ventilators support non-invasive ventilation, equipped with common non-invasive ventilation modes such as PSV-S/T, CPAP/PSV, P-A/C, etc., with the leak compensation up to 65 L/min. The ventilator is used with a dual-limb circuit with a closed non-invasive mask to support NIV. During the ventilation, VTi (insp. tidal volume), VTe(exp. tidal volume), MVleak (leaked volume in a minute) and leak% (percent of leaked tidal volume) can all be closely monitored.
When providing respiratory support for COVID-19 patients, the use of non-invasive ventilation with dual-limb circuits can greatly reduce the amount of gas exhale into the atmosphere (compared with traditional single-limb circuit expiratory valve). At the same time, with additional filter at the expiratory valve can efficiently process the exhaled air, and reduce the risk of aerosol infection to a minimal level.
High-Flow Oxygen Therapy (HFOT)
1. Clinical Consensus
When PaO2/FiO2 is between 200 mmHg and 300 mmHg, it is advised that the patient is supported with high-ﬂow oxygen therapy (HFOT) through nasal cannula (commonly called HFNC or HFNOT). The initial setting of HFNC can be at 40 - 50L/min with 100% FiO2. During the therapy, clinicians should closely observe the patient’s vital signs and oxygenation.
If the oxygenation deteriorates to PaO2/FiO2 < 200 mmHg, or SpO2 falls below 93%, and/or the RR is above 30 times/min, then HFNC is not likely to be eﬀective and NIV may be a better choice in this case.
If the patient has any of the following symptom, invasive ventilation should be used instead of HFOT:
- severe arrhythmia;
- shock (intravenous norepinephrine dosage> 0.1 μg/kgmin);
- acute respiratory acidosis (pH < 7.25);
- airway obstruction.
2. Solutions for HFOT
Compared with the standard oxygen therapy, Mindray’s SV Series ventilator’s HFOT can provide 2 - 60 L/min flow of oxygen and up to 100% FiO2. In addition, with humidifier to actively warm and humidify the HFOT’s gas flow delivered to patients, preventing mucociliary damage, sputum buildup, and other complications. Autopsy reports shown that COVID-19 lesions are concentrated in the lungs with a large amount of viscous sputum. Therefore, humidified HFOT has a great significance for patients requiring sputum clearance.
 Critical Care Committee of Chinese Association of Chest Physician, Respiratory and Critical Care Group of Chinese Thoracic Society, Respiratory Care Group of Chinese Thoracic Society. Conventional respiratory support therapy for Severe Acute Respiratory Infections (SARI): Clinical indications and nosocomial infection prevention and control.
 Experts’ Suggestions on Clinical Management of Severe Cases of COVID-19. Chinese Journal of Critical Care & Intensive Care Medicine [e-Journal]. 2020, 06.
 World Health Organization. Clinical management of severe acute respiratory infection when Novel coronavirus (2019-nCoV) infection is suspected: Interim Guidance. 2020 Jan 28.
 Marini JJ. Recruitment maneuvers to achieve an ‘open lung’: whether and how? Crit Care Med 2001; 29:1647–1648.
 Halter JM et al. Positive End-Expiratory Pressure after a Recruitment Maneuver Prevents Both Alveolar Collapse and Recruitment/Derecruitment. Am J Respir Crit Care Med 2003; 167: 1620-1626.
 Chen et al. Implementing a bedside assessment of respiratory mechanics in patients with acute respiratory distress syndrome. Critical Care (2017) 21:84.