High-Flow Oxygen During the COVID-19 Pandemic

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Salient features:

This article focuses on:

  • Definition
  • Rationale
  • Review
  • Conclusion

Detailed summary:

Definition:

  • High-flow nasal cannula (HFNC) is comprised of an air/oxygen blender, humidifier, heated circuit, and nasal cannula.
  • Medical gas is heated and humidified and delivered at up to 60 L/min.
  • HFNC improves patient flow matching, provides Positive End-Expiratory Pressure (PEEP), reduces anatomic dead space and improves patient comfort when compared to supplemental oxygen by nasal cannula.

Rationale:

  • The current COVID-19 pandemic is causing global mortality and overwhelming healthcare systems internationally.
  • HFNC reduces the need for mechanical ventilation in acute hypoxemic respiratory failure in a general ICU population.
  • Placing COVID-19 patients on HFNC prevents intubation and mechanical ventilation, which likely facilitates earlier mobilization, reduces respiratory muscle atrophy, and results in shorter ICU and hospital length of stay to help reduce resource strain.
  • Extubating HFNC facilitates earlier mobilization and reduced length of stay.
  • The World Health Organization (WHO), Society of Critical Care Medicine (SCCM), European Society of Intensive Care Medicine (ESICM), Australian and New Zealand Intensive Care Society (ANZICS) and Chinese Medical Association recommend the use of HFNC in COVID-19 with respiratory failure.
  • However, HFNC may be an aerosol generating medical procedure that increases the risk of nosocomial transmission of COVID-19.

Review :

  • Hui et al.investigated exhaled air dispersion using a high-fidelity human patient simulator.
  • They have tested multiple oxygen delivery modalities in an experimental design where smoke was delivered to the simulator’s right main bronchus and exhaled smoke dispersion was measured using laser illumination and motion video.
  • These studies were done under a negative pressure room, with titrated doses of oxygen, pressure, or flow, and with modifiable simulated oxygen consumption, lung compliance, respiratory rate, and tidal volume.
  • According to the data, HFNC cause less air dispersion than normal nasal cannula.
  • HFNC does not increase dispersion of aerosols in healthy volunteers compared to no HFNC.
  • A retrospective Canadian study looking at risk factors for SARS transmission from patients requiring intubation to healthcare workers estimated HFNC to be protective; however, this result was not statistically significant.
  • This is compared to intubation having a pooled odds ratio of 6.6 for transmission of SARS to healthcare workers and additional data from the SARS outbreak in Toronto also suggesting intubation is a procedure with a high risk of transmission.
  • HFNC have also been found to not be associated with increased air or contact contamination from patients with gram negative pneumonia when compared to oxygen mask.

Conclusion:

  • The above data are supportive of a hypothesis that HFNC may possibly be beneficial in reducing transmission of COVID-19.
  • There is biologic plausibility given humidified air leads to larger droplets and other lipid enveloped coronaviruses have demonstrated shorter survival time with increased relative humidity.
  • Therefore, it is suggested that there should be comfort in using HFNC in COVID-19 patients as there is no clear risk of increased transmission from the available data.
  • Treatment failure and subsequent emergent intubation should still be avoided as it poses an increased risk of healthcare worker transmission to the intubation team.
  • HFNC may be considered preferentially over oxygen by nasal cannula even at lower levels of required oxygen as HFNC may be safer from an infection transmission perspective.
  • Healthcare workers should use an N95 respirator in addition to other personal protective equipment when caring for patients on HFNC.

Reference Link: http://www.bccdc.ca/Health-Professionals-Site/Documents/COVID19_HighFlowOxygenRecommendations.pdf

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