Respiratory support in suspected COVID-19 patients. When conventional O2 therapy is not enough!

We talk about evidences on respiratory support in the dyspneic and moderately/severe hypoxic suspect COVID-19 patient on the field. Clinical evidences and contamination risks in the potentially infected COV 19 patients to guide our efforts toward a good outcome when the conventional O2 therapy is not enough.

A step backward

The COVID-19 pneumonia. More than a “baby lung”

Clinical features and Imaging in early phases

• Mild dyspnea
• Severe hypoxia
• Low P/F ratio
• Respiratory failure
• Lung failure
• ARDS pattern
• Ground glass
• Crazy paving

Clinical characteristics and imaging manifestations of the 2019 novel coronavirus disease (COVID-19):A multi-center study in Wenzhou city, Zhejiang, China

The imaging pattern of multifocal peripheral ground glass or mixed opacity with predominance in the lower lung is highly suspicious of COVID-19 in the first week of disease onset. 

Lung mechanics

• High compliance
• Low driving pressure
• Reclutability
• PEEP responsive

Clinical features OneLevel respiratory support

• It’s not a ventilation but a spontaneous breathing on a fixed one expiratory level pressure. No inspiratory support.
• Give a tritrable PEEP in the highly reclutable and “PEEP responsive” COVID-19 lung

Clinical features BiLevel respiratory support

• It’s a proper ventilation on two level pressure
• Give expiratory and inspiratory support with a tritrable driving pressure

Risk benefits assessment

More risk patient level

• Patient may become agitated or combative due to hypoxia
• Patient PPE must be removed
• Clinicians are in close proximity to the patient’s airway
• Aerosol generating events are more likely

More risk device level

• High flow oxygen
• Aerosol generation procedure
• Poor mask sealing
• Continuous manipulation at the mask/strap level to optimise sealing and patients compliance

Droplet spreading. OneLevel VS BiLevel respiratory support

DSC Hui, MTV Chan, B Chow. Aerosol dispersion during various respiratory therapies: a risk assessment model of nosocomial infection to health care workers. Hong Kong Med J 2014;20(Suppl 4):S9-13

When inspiratory positive airway pressure (IPAP) increased from 10 to 18 cmH2O, the exhaled air of a low normalised concentration through the ComfortFull 2 mask increased from 0.65 to 0.85 m at a direction perpendicular to the head of the HPS along the median sagittal plane. In contrast, when an IPAP of 10 cmH2O was applied via the Image 3 mask connected to the whisper swivel exhalation port, the exhaled air dispersed to 0.95 m towards the end of the bed along the median sagittal plane, whereas a higher IPAP resulted in wider spread of a higher concentration of smoke (….) It is also important to avoid the use of higher IPAP, which could lead to wider distribution of exhaled air and substantial room contamination.

Prehospital strategy and practical tips

When high flow conventional O2 therapy is not enough to reach clinical goals in the highly risk patient, non otherwise transportable and at risk of rapidly loosing airway patency One level PEEP respiratory support (CPAP) is the best compromise between clinical efficacy and contamination risk.

Ventilatory inspiratory support (BiPAP) doesn’t add much from a clinical point of view and increase the risk of contamination so has to be avoided.

Practical tips when using CPAP on the field

• Use a non ventilated elbow to prevent risk of dissemination
• Use a filter between the mask and the patient to prevent risk of contamination

References

1. Wenjie Yang et al. Clinical characteristics and imaging manifestations of the 2019 novel coronavirus disease (COVID-19):A multi-center study in Wenzhou city, Zhejiang, China. Journal of Infection. 2020
2. Hui DS, Chow BK, NG SS, et al. Exhaled air dispersion distances during noninvasive ventilation via different Respironics face masks. Chest 2009;136:998-1005.
3. Randy S. Wax, MD. Practical recommendations for critical care and anesthesiology teams caring for novel coronavirus (2019-nCoV) patients, Can J Anesth/J Can Anesth. https://doi.org/10.1007/s12630-020-01591-x
4. WHO. Clinical management of severe acute respiratory infection (SARI) when COVID-19 disease is suspected. Interim guidance 13 March 2020
5. Xiaobo Yang, Yuan Yu. Clinical course and outcomes of critically ill patients with SARS-CoV-2 pneumonia in Wuhan, China: a single-centered, retrospective, observational study. http://www.thelancet.com/respiratory
6. David J Brewster , Nicholas C Chrimes. Consensus statement: Safe Airway Society principles of airway management and tracheal intubation specific to the COVID-19 adult patient group.