It was found that SARS-CoV‐2 viral in sputum and upper respiratory secretions was the highest [22], which caused the world’s attention to reduce the occupational safety of medical workers. In the process of endotracheal intubation, anesthesia resuscitation, extubation, tracheotomy, and tracheotomy tube replacement, medical workers may be infected with various viruses and bacteria other than SARS-CoV-2 [10], which seriously threatens the health of medical workers.

To reduce viral exposure during sputum aspiration, endotracheal intubation, bronchoscopy, and tracheostomy, efforts have been made to standardize clinical procedures and develop personal protective equipments [5]. For example, some scholars suggested that medical workers should use 5 min of preoxygenation with 100% oxygen, rapid sequence induction techniques, and small tidal volume manual ventilation to avoid potential aerosolization of the virus from patient’s airways [23, 24]. An “aerosol box”, consisting of a transparent plastic cube designed to cover the patient’s head, contains two circular ports through which the doctor’s hands perform the airway procedures, reportedly effectively blocking the spatter of the patient’s airway secretions [6, 25, 26]. In addition, a sufficiently large (> 100 cm × 100 cm is recommended) PVC membrane with a hole (sealed when necessary) in the center for the connection between the face mask and the circuit has been reported to similarly control the source of infection and enhance the protective measures of medical workers [1]. During the epidemic, all of the above measures played a role in protecting medical workers in around the world. However, after the epidemic is under control, the complicated and costly protective measures are not applicable. Therefore, it is necessary to develop an airway secretion blocking device that is simple to operate, easy to remove after use without contaminating the users and suitable for reducing the transmission risk of potential diseases.

Direct contact with large droplets from infected persons and contaminated fomites is considered to be the main route of transmission of respiratory viruses [8]. A large number of studies on the distance of horizontal droplet showed that the propagation distance of droplets was more than 2 m, or even more than 8 m in some cases [9, 27]. In this study, we designed a series of “safety cap” that can be connected to the opening of endotracheal tube or tracheotomy tube. The cough-splash simulation experiments using phosphor suspension or E. coli suspension to simulate respiratory secretions showed that the use of “safety cap” can significantly limit the spraying range of respiratory secretions and significantly reduce the component of sprayed secretions, indicating that “safety cap” can significantly improve the hospital sanitation and reduce the transmission risk of various pathogens carried by respiratory secretions.

Clinical practice has proven the effectiveness of bacteria/virus filters in limiting the transmission of respiratory microorganisms, but we believe that the bacterial filter will greatly increase the respiratory resistance of patients and may not be suitable for patients who have undergone a tracheostomy procedure and need to replace tracheotomy tube (inner cannulas), as well as for patients who are being extubated and waiting for spontaneous breathing recovery. Through this study, we provide an alternative protective solution. In this study, our main objective was to investigate the effectiveness of using a “safety cap” to block respiratory secretions expelled during endotracheal intubation, extubation (including the process of waiting for patients to regain sufficient strength for autonomous breathing), and regular replacement of tracheotomy tube (inner cannulas) in patients who have undergone a tracheostomy procedure, thereby preventing direct contamination (Respiratory secretions are directly sprayed onto medical workers) of medical workers’ faces and bodies by patient respiratory secretions. We believe that no medical workers would want patient respiratory secretions sprayed onto their face. Although the use of a “safety cap” may not completely prevent disease transmission caused by aerosol leakage, it can significantly reduce direct exposure of medical workers’ faces, clothing, and skin to patient respiratory secretions, thus improving the hospital sanitation and reducing (rather than eliminating) potential risks associated with disease transmission.

The “safety cap” has advantages of low cost, simple operation, and a good protective effect. Based on this study, we propose that “safety cap” may be applicable to the following 3 clinical procedures that are prone to causing patient coughing. However, the practicality and effectiveness of limiting airway secretion spread in these use cases still require thorough research for further validation [1]. Before endotracheal intubation, the “safety cap” can be connected to the endotracheal tube opening to prevent the respiratory secretions emitted by patients when coughing and to prevent pollution to the medical workers [2]. Before extubation, the “safety cap” can be connected to the endotracheal tube opening to block the airway secretions, which may carry pathogenic microorganisms when the patient coughs [3]. In the process of tracheotomy tube replacement, connecting the “safety cap” to the tracheotomy tube opening may effectively block the respiratory secretions sprayed by patients, and effectively reduce the occupational exposure risk of medical workers. It is essential to emphasize that these potential clinical applications are based on the results of simulated experiments and will require further validation through future clinical trials.

However, this study still has certain limitations, as the “disposable pulse irrigator” sprays liquid/air at a rate of 900 ± 300 mL/min in a pulse, it is not a true cough, since the speed of cough flow can be as high as 300 L/min. Additionally, the patients undergoing intubation usually receive sedation and paralytics, which suppress coughing and spontaneous breathing. Once the endotracheal tube is inserted and connected to a ventilator, the exposure time to the patient’s lower airway is very short, resulting in a low risk of generating aerosols, especially bioaerosols [28]. Placing the “safety cap” on the endotracheal tube during insertion may hinder visibility and increase weight, potentially making it more difficult to manipulate and pass the tube through the vocal cords. The secretions in the oral cavity and trachea can still be expectorated through the gap between the endotracheal tube and the trachea if the cuff is not inflated. Furthermore, extubation may generate some aerosols; however, when patients are ready for extubation, the risk of transmission from exhaled aerosols is very low due to resolved or improved infection. Therefore, the exact role of “safety cap” is to prevent patients from spraying respiratory secretions directly to the operator during airway management, especially in the process of replacing the tracheotomy tube in patients who had undergone tracheotomy, improve the hospital sanitation and reduce the transmission risk of potential diseases.

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