Prevention of airborne transmission during respiratory support of COVID-19
More than a million people worldwide have been infected by COVID-19 with thousands of medical staff included. WHO declared the COVID-19 a pandemic on March 11th recently stated that “When health workers are at risk, we’re all at risk”. This is why the urgent demand for personal protective equipment is at an all-time high. Healthcare workers are exposed to respiratory hazards in various forms, mainly airborne inhalation and droplets from an infected person. Diseases, which respect no national boundaries, can challenge efforts to protect workers especially handling patients with COVID-19. Healthcare workers can protect themselves when caring for patients by adhering to infection prevention and control practices, including appropriate use of engineering controls, administrative controls, and personal protective equipment (PPE).
Patients with severe COVID-19 should select the appropriate respiratory support therapy based on the severity of hypoxemia. For COVID-19 patients with mild to moderate hypoxemia, oxygen therapy with nasal cannula or simple oxygen masks, nasal high-flow oxygen therapy, and non-invasive ventilation (NIV) are the preferred for respiratory support. NIV, invasive mechanical ventilation (IMV), and external membrane oxygenation (ECMO) are used for moderate to severe hypoxemic patients. Due to the characteristic of airborne transmission in COVID-19 patients, droplets and aerosols from the patient presents a great challenge for prevention and control of infection under different respiratory therapy strategies.
Patient airway management personal protective equipment (PPE) configurations
Reducing Aerosol Dispersion during Nasal Cannula or Nasal High-Flow Oxygen Therapy
Nasal cannula oxygen therapy (NCOT) and high-flow nasal cannula oxygen therapy (HFNCOT) are open-system oxygen delivery methods. With humidification, the flow of oxygen generates a large amount of aerosols which may carry virus. In addition, the high-speed oxygen flow can further aid the spread of virus-containing aerosols to the surrounding environment, which increases the risk of infection for the healthcare workers.
Correctly wearing of surgical or N95 masks for patients can significantly reduce the spread of virus-containing aerosols during coughing and breathing. Some researchers have combined N95 masks with nasal cannula to design a new type of oxygen therapy mask, which can effectively reduce the aerosol transmission. Airtight sealed masks with bacterial and viral filters are also believed to effectively reduce aerosol diffusion.
Reducing Aerosol Dispersion during Non-Invasive Ventilation
Based on multiple studies of SARS, H1N1, it has been proved that non-invasive ventilation may cause aerosol dispersion, increasing the risk of infection. Guidelines from the European Respiratory Society / European Society of Intensive Care (ERS/ESICM), the World Health Organization (WHO), the National Health Service (NHS), the Hong Kong Chest and Lung Foundation, and the American Respiratory Therapy Association (AARC) suggest that during an epidemic of infectious diseases, non-invasive ventilation is still a high-risk therapy which requires extensive prevention. However, experience from many front-line pulmonary critical care experts in Wuhan, shows that many severe patients with mild/moderate hypoxemia can be effectively treated with non-invasive ventilation (NIV).
Establishing Artificial Airways: When and How
Critically ill COVID-19 patients require mechanical ventilation in the event of severe hypoxemia and respiratory distress. Related clinical studies of MERS, SARS, and influenza have shown that NIV has a higher failure rate for such patients, and delayed intubation may increase patient mortality. According to the experience by clinical experts in this round of pandemic, COVID-19 patients have a slower progression of respiratory failure compared with SARS patients. In addition, some patients with severe respiratory failure can still be successfully treated with NIV. It is still recommended to use NIV as preliminary support while invasive ventilation should be established immediately if the following patient condition occurs:
The principle of establishing an artificial airway is to minimize coughing and the transmission of droplets in patients. Endotracheal intubation is divided into two types: oral and nasal. It is highly recommended to operate this therapy with Grade-3 prevention standards, with oral endotracheal intubation preferred. Try to avoid the use of ordinary laryngoscope, which will stimulate the glottis and cause a large amount of airway secretions to be expelled. Electronic laryngoscope or bronchoscope can be used to guide the insertion to reduce operator exposure time during intubation. When there is a contraindication to oral intubation, nasal tracheal intubation under the guidance of a bronchoscope can be used as an alternative.
Since it is difficult to use the bronchoscope when using positive pressure headgear, an electronic bronchoscope should be used whenever possible. The use of electronic bronchoscopes can also avoid being too close to the patient, reducing the chance of contamination from splatters. Due to high risk of sputum and blood splatter, tracheotomy is not the initial option.
Preventive Measures during Tracheal Intubation
When patients require intubation, careful prevention and control measures must be taken in three aspects: the operator, the patient, and the environment. During intubation, the operator should avoid repeated attempts to reduce exposure. When performing intubation, the operator shall follow Grade-3 protection standards and wear protective equipment. It is recommended to quickly intubate in combination with sedatives, analgesics and neuromuscular blockade to reduce coughing. Intubation should be performed in a negative pressure ward, which can effectively reduce the risk of infection to the medical workers.
Suctioning during Invasive Mechanical Ventilation
For patients relying on artificial airways, it is strongly recommended that a closed-suctioning device should be used for this therapy. It should be determined carefully whether the patient requires suctioning or not, to avoid frequent and unnecessary suctioning, which may lead to discomfort or cause severe coughing. Suctioning may be considered if and when the patient has the following clinical manifestations:
For patient requiring high FiO2 or positive end-expiratory pressure (PEEP) and/or shows significant deterioration of vital signs, pre-oxygenation should be performed for 2 minutes before suction to avoid hypoxemia during suctioning. Disconnecting the ventilator circuit may cause alveolar collapse and large transmission of droplets and aerosol. Therefore, it is recommended to use closed-suction, to reduce the risk of pathogen transmission.
Shallow suctioning can be used to avoid mucosal edema, inflammation, severe coughing, and even bleeding caused by the stimulation of carina and airway. Each suction period is preferably < 15 seconds, and continuous negative pressure should be performed and maintained between 80 and 150 mmHg during suctioning. The closed-suction should be replaced every 24 hours.
Unless required by the patient, conventional bronchoscopy is not recommended for suctioning. Unless necessary, make sure that a three-way connector (i.e. T-Piece) is used to avoid disconnection of the breathing circuit!
Critical Respiratory Medicine Group at the Respiratory Medicine Branch of the Chinese Medical Association, Critical Care Medical Working Committee at the Respiratory Medicine Branch of the Chinese Medical Doctor Association. Recommendations for Airway Management in Adults with Severe Novel Coronavirus Pneumonia (Trial). Chinese Medical Journal, 2020,100 (00): E004-E004. DOI: 10.3760 / cma.j.issn.0376-2491.2020.0004