Respiratory support is required for stage four and five Covid-19 patients to maintain target peripheral oxygen saturation (SpO2) of 90-96%. The types of respiratory support include oxygenation with low flow or high-flow system, noninvasive ventilation (NIV) and mechanical ventilation (intubation). (1)
A brief overview of the types of respiratory support is as below:
Low Flow System
The initial supplemental oxygenation support is delivered with a low flow system (up to 6 L/minute) via nasal cannula. As patients progress, a higher amount of oxygen is required and higher flows of oxygen (up to 10-15 L/min) can be administered through a low flow system with a simple face mask, venturi mask or non-rebreather mask. (1)
High-flow System
High flow oxygen delivered via a nasal cannula (HFNC) is commonly used in Covid-19 when oxygen requirement increased above 6-15L/min. HFNC is the preferred option compared to NIV unless there is a concomitant indication such as acute hypercapnia requiring bi-level positive airway pressure. Compared to NIV, HFNC is generally more comfortable for patients as they can continue to talk and eat. The high failure rate of NIV in the Middle East respiratory syndrome (MERS) and other non-COVID-19-related causes of acute respiratory distress syndrome (ARDS) favours HFNC over NIV in Covid-19. (1)
High flow nasal cannula (HFNC) delivery system (2)
Non-invasive ventilation (NIV)
Current evidence of efficacy for NIV in non-covid indications include acute hypercapnic respiratory failure from an acute exacerbation of chronic obstructive pulmonary disease (AECOPD), acute cardiogenic pulmonary oedema, and patients with underlying sleep-disordered breathing (eg, obstructive sleep apnea or obesity hypoventilation). (1)
For Covid-19 patients, there is no significant difference in treatment duration, rate of progression to invasive mechanical ventilation and mortality among patients initiated with either HFNC or NIV. (3)
Non-invasive ventilation (NIV) (4)
Mechanical Ventilation
Patients on non-mechanical ventilation should be monitored closely on clinical features and blood gas parameters. Patients who deteriorated further, as below, will be intubated: (1)
Rapidly deteriorated over hours
Persistently need of high flows/fraction of oxygen (>60 L/minute and an FiO2 >0.6)
Evolving hypercapnia, increasing work of breathing, decreasing tidal volume, worsening mental status, increasing duration and depth of desaturations
Hemodynamic instability or multiorgan failure
Mechanical ventilation (5)
Prone Position
Prone position assists the opening of collapsed dorsal alveoli and leads to better gas exchange and oxygenation. Prone position has been extensively practised in spontaneously breathing patients receiving HFNC or NIV with the objective of improving oxygenation, reducing intubation rate and ICU admission. It is encouraged for patients to spend at least 6 to 8 hours prone in a 24 hour period. (1)
In mechanically ventilated ARDS patients, the prone position is clearly recommended. However, it is uncertain for a prone position in awake Covid-19 patients.
Prone position (9)
A systematic review and meta-analysis of non-randomized trials found (6):
Patients with prone position were associated with a statistically significant higher PaO₂/FiO₂ ratio as compared to the supine group (primary outcome)
Patients with prone position were associated with a statistically significant higher SpO₂ as compared to the supine group (secondary outcome)
The prone group had a statistically significant lower mortality rate than the supine group (secondary outcome)
No significant differences were noted between the prone and supine groups in the incidence of intubation and numbers of patients discharged alive (secondary outcome)
Further studies are needed to standardize the regime of prone position to improve the certainty of the evidence, as the studies included were limited in number, with small sample size and had substantial heterogeneity of measured outcomes.
World Health Organisation (WHO) has come out with conditional recommendations and the British Thoracic Society/ Intensive Care Society (BTS/ICS) has a suggested pathway with regards to the prone position in respiratory support in Covid-19. (7,8)
References
Anesi GL. COVID-19: Respiratory care of the nonintubated critically ill adult (high flow oxygen, noninvasive ventilation, and intubation). UpToDate. https://www.uptodate.com/contents/covid-19-respiratory-care-of-the-nonintubated-critically-ill-adult-high-flow-oxygen-noninvasive-ventilation-and-intubation? Accessed September 2, 2021.
Spicuzza L, Schisano M. High-flow nasal cannula oxygen therapy as an emerging option for respiratory failure: the present and the future. Ther Adv Chronic Dis. 2020;11:2040622320920106. Published 2020 May 13. doi:10.1177/2040622320920106
Shoukri AM. High flow nasal cannula oxygen and non-invasive mechanical ventilation in management of COVID-19 patients with acute respiratory failure: A retrospective observational study. The Egyptian Journal of Bronchology. 2021;15(1). doi:10.1186/s43168-021-00063-0
Non invasive ventilation. Physiopedia. https://www.physio-pedia.com/Non_Invasive_Ventilation. Accessed September 2, 2021.
Elliot ZJ, Elliot SC. An overview of mechanical ventilation in the Intensive Care Unit. Nursing Standard. 2018;32(28):41-49. doi:10.7748/ns.2018.e10710
Chua EX, Zahir SMISM, Ng KT, et al. Effect of prone versus supine position in COVID-19 patients: A systematic review and meta-analysis [published online ahead of print, 2021 Jun 22]. J Clin Anesth. 2021;74:110406. doi:10.1016/j.jclinane.2021.110406
Covid-19 clinical management: Living guidance. World Health Organization. https://www.who.int/publications/i/item/WHO-2019-nCoV-clinical-2021-1. Accessed September 2, 2021.
Messer B, Antoine-Pitterson P, Blundell A. BTS/ICS Guidance: Respiratory Care in Patients with Acute Hypoxaemic Respiratory Failure Associated with COVID-19. British Thoracic Society/Intensive Care Society. https://www.brit-thoracic.org.uk/document-library/quality-improvement/covid-19/btsics-guidance-respiratory-care-in-patients-with-acute-hypoxaemic-respiratory-failure-associated-with-covid-19/. Accessed September 2, 2021.
Without oxygen cylinder, octogenarian beats Covid by adopting prone position. OnManorama. https://www.onmanorama.com/lifestyle/health/2021/04/27/octogenarian-beats-covid-adopting-prone-position.html. Accessed September 2, 2021.
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