Optimizing Respiratory Care for Patients While Protecting Ourselves

The COVID-19 pandemic has taught us a lot. One vital lesson learned by the respiratory community has been differentiating the risks of aerosol transmission and the classification of aerosol-generating procedures (AGPs).

During the early pandemic, several experimental studies reported live virus from aerosols and surfaces hours after inoculation,^1,2 resulting in concerns of aerosol transmission. We were reluctant to use noninvasive respiratory support such as high-flow nasal cannula (HFNC) oxygen therapy, CPAP, or noninvasive ventilation (NIV) to treat patients with COVID-19; and instead, we took an aggressive intubation strategy, which contributed to the crisis of ventilator shortage.^3,4 Since then, numerous studies have been conducted to understand viral transmission via aerosols.^5-11 Study types included those that indirectly quantified aerosol particle concentrations,^6,7 aerosol dispersion distances and travel trajectory,⁸ as well as direct measurements of viruses in aerosols.^9-11 To date, no studies have reported higher risks of virus transmission when HFNC, CPAP, or NIV is used compared to conventional oxygen therapy or invasive mechanical ventilation.^6-11 As a result, many institutions have removed HFNC, CPAP, and NIV from their AGP list.¹² Not surprisingly, these institutions have reported avoidance of intubation for patients with COVID-19 by using noninvasive respiratory support.^13,14

In this issue of the Journal, 2 studies report direct evidence of viral detection during NIV and HFNC in COVID-19^15,16 in which the findings further support removing them from the AGP lists. The results also suggest that clinicians can be confident in using noninvasive modalities safely. Dell’Olio¹⁵ et al investigated the presence of SARS-CoV-2 on surfaces near subjects with COVID-19 receiving NIV at 4 distances (50, 80, 150, and 200 cm). The samples were taken immediately and 6, 12, and 24 h after surface disinfection. Two-hundred fifty-six samples were collected, and none were positive for SARS-CoV-2.¹⁵ Ramsey and colleagues¹⁶ attempted different sampling methods to capture SARS-CoV-2 virus in the vicinity of 37 subjects with COVID-19 during noninvasive respiratory support, primarily HFNC. Thirty-one subjects had saliva samples tested at the time of aerosol sample collection, with 14 positive for SARS-CoV-2 RNA. Initially, the authors used vacuum pumps at a low flow (5 L/min) to capture aerosol samples at 30–45 cm in front of the subjects for 20–90 min, which collected 100–450 L of air. None of the samples were positive. Then they placed vacuum pumps at higher flows (80–90 L/min) to capture 2,500–6,000 L of air samples at 2–3 m from the subject’s bed and still did not detect any virus. They also devised a scavenger face tent to directly capture aerosol samples from the subject’s airway overnight, with a vacuum flow of 30 L/min, which collected > 10,000 L of air, with a corresponding sampling limit of detection of approximately 0.01 viral particles/L.¹⁶ At such high sensitivity and close proximity, samples from the 4 subjects using a scavenger face tent turned out to be positive. Among the 4 subjects, one had a negative saliva sample; but the aerosol sample was positive, implying that the exposure dose to infectious aerosols was very low. Both studies suggested a low risk of aerosol transmission of SARS-CoV-2 with the use of HFNC and NIV.^15,16

Compared to aerosol particle concentrations generated during breathing room air, conventional oxygen therapy, HFNC, CPAP, or NIV, aerosol particle concentrations generated by coughing or sneezing are hundreds of fold higher.^5,12 Bioaerosols generated by coughing or sneezing that come from airways have been shown to carry pathogens.¹⁷ Thus, procedures or treatments that provoke patients to cough or sneeze remain as a clinical concern. When patients are coughing or sneezing, they need to cover their face with a mask, tissue, or elbow. They can cough at any time during the utilization of noninvasive respiratory support. When HFNC or NIV is used, placing a surgical mask over HFNC^7,8 or using dual-limb ventilators and placing filters on the exhalation ports during NIV^15,16 can help significantly reduce the bioaerosol particle concentrations. Indeed, mitigation strategies were taken in these 2 studies;^15,16 they also used high room ventilation and air exchanges (4–6 exchanges per hour in Ramsey et al¹⁶ and 10 exchanges per hour in Dell’Olio et al¹⁵). The results of almost no detection of the SARS-CoV-2 virus might imply that these mitigation measures are effective.^15,16

Bioaerosol transmission can be interrupted by reducing the concentrations of pathogens generated at the source, impeding pathogen transportation and protecting the host.^3,17 In addition to mitigating bioaerosol generation and transportation, personal protection equipment is also effective at interrupting transmission. Lastly, we should be aware that the outcome of host-viral interactions depends on the dose and route of infection, viral virulence properties, as well as several host factors that mainly involve innate and adaptive immunity.¹⁸ Vaccination helps build immunity, reducing the risk of severe illness.

Both studies were initiated during the early pandemic (April 2020),^15,16 when medical facilities were overwhelmed with COVID-19 patients, especially bedside clinicians. These authors took on additional work to seek evidence of aerosol transmission and should be congratulated and appreciated for their efforts. Their findings,^15,16 along with many others,^5-12 demonstrate great examples of how research changes clinical practice and why such evidence is essential to the practice of evidence-based medicine. These lessons learned from the COVID-19 pandemic prepare us to better deal with future pandemics, as we know how to use available tools to optimize care for patients while protecting ourselves.

• Copyright © 2023 by Daedalus Enterprises